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0:06
Hello, welcome back! You are now here for Section 3: The Theory of Plate Tectonics. What an appropriate topic to begin the journey of the rest of our course! So you've been learning a little bit about geologic principles and dynamo earth. Now we're going to take it to the next level. This is such a foundational piece of geology to understand why we have continental drift which is plates moving. Lithosphere plates we learned about in dynamo earth. Why we have island arcs?
0:46
Why do we have mountains in some places yet not others? Why do we have volcanoes in some regions, yet we have earthquakes in others? So all of these questions are related to this topic. But plate tectonics when you consider other sciences is a very new concept. Well, it's been around for over a hundred years the idea... It really didn't get proved until after World War II. So let's take a look at the theory of plate tectonics. And I'm going to start here.
1:19
I mentioned this when we were in geologic principles, but I want to take a moment to tell you what you're seeing, and then we'll revisit it later in our lecture experience. So I'm in a helicopter flying over a lava tube, and you can see some of the smoke here. So the lava tubes are coming in this direction, and they're draining in lava into the Pacific Ocean, And this big cloud of smoke you see is called a hydrovolcanic eruption. This is part of evidence that plate tectonics is real.
1:56
Continental drift is real. Seafloor spreading may not relate to this particular site, but it's all part of the equation of plate tectonics So as we go through this, I'm gonna give you a little history background and then we're going to talk about the science part, but the history is key to understanding how we got to a place that we could even begin to do the scientific method approach to proving Alfred Wegener was spot on. So, this is Alfred Wegener
2:27
Gee, he's my favorite geologist of all time! I just love him! And one of the reasons I do is because he was a forward thinker. He also was an action-based guy - to the point where he died for his cause. If you want to kind of look up on Google and do some search on who Alfred Wegener was and where he died. It's kind of a sad story, but he was trying to prove his theory of continental drift. So he is considered the father of continental drift, not plate tectonics.
2:59
That's a different ballgame altogether, But Alfred Wegener proposed in his book in the early 1900's; Hey, I believe that there was a supercontinent at one point, and he thought it was gonna be at a certain place on the geologic timescale, specifically at the end of the Pennsylvanian Early Permian Period. So late Paleozoic... and he called this place "All Lands." So you'll see Pangaea spelled two ways: the way I have it here which is the way it's in his book,
3:34
and then you'll actually just see it with a "g-e-a", instead of an "a-e-a". I would prefer that you spell it correctly, but it's not one of those things that's a deal breaker because it's written in both ways in literature across the world. So some of the proof that Wegener provided I think would have passed in a jury in a courtroom today. So I want to see what you think after we go through this --
3:59
if you would have voted as a jury to say, "Acquittal. Yep, I believe this is a deal; continental drift is real." Or you would say, "Nope, I think more evidence was needed. Nope, not gonna happen. Sorry -- next time." So we're gonna look at those pieces of evidence, and then I'm gonna tell you kind of what happened to get the evidence that needed to happen for the rest of the scientific community to buy off on Wegener's theories. So his initial theory was that Pangaea joined together;
4:35
It started in the early Permian period. So if you get your geologic time scale out, you have one in Chapter One, and you'll also have one in Chapter Ten, but I want you to get the one out in Chapter One, and you're gonna see that there's seven periods in the Paleozoic era: Cambrian Ordovician Silurian Devonian Mississippian Pennsylvanian Permian. So the Permian period represented when all the plates were together. So there's two sections of plates;
5:09
There's the southern ones which are called Gondwanaland. Gondwana for short is fine. And then Laurasia are all the northern continents. Now kind of an important misnomer here: There's a little continent that gets people confused. That's what's part of Gondwanaland that's clearly in the northern hemisphere today, and it's this dude right here. So India separated. You can see it beginning to separate from Permian to Triassic. You begin to see an ocean basin happening here.
5:41
So that's the result a continental rifting. RIFTING, and then you can see that India breaks off here and begins to move, at a fairly rapid pace I might add, and eventually in modern-day, smush in to what we know as Asia or Laurasia. So we are going to take a look at how Wegener showed with his evidence to the scientific community "jury" that he thought continental drift was real. First thing was the geometric fit of continents.
6:17
I can remember when I was probably four or five, I was piecing together a puzzle of the world, and I was like, "Mom! Look! The continents fit like they were once together!" and she -- my mom is a scientist, so you have to appreciate -- so is my dad -- he was a surgeon, and mom was a medical technician. So they'd had bunches of science, but when they went through school, plate tectonics was not a thing, and so while she knew these were together,
6:45
and she knew about plate tectonics, she just kind of laughed. To her credit, she didn't say anything like, "Duh! Of course, they fit together because they once were together." What is bigger than just the geometric fit is the scientific community folks that were like, "Oh, this can't be." Said, "Okay, Wegener, they may fit together, but that could just be a happenchance, literally a fluke because they eroded and they're perfectly fit together."
7:17
The shoreline certainly would be eroding out, and weathering at a regular basis, so they had a point. However, that geometric fit of continents would prove to be spot-on, and we're going to see where that is in just a few minutes. Second piece of evidence that Wegener had had to do with the rocks of these touching continents like from Africa to North America and Europe to North America. Starting in the Devonian which is the middle of the Paleozoic all the way through the end of the Paleozoic,
7:50
there are rock layers that match in these continents, but now they're separated by an ocean basin like the Atlantic. And in terms of Europe when these rocks date to the same age, same composition... Of course, they didn't have all the tools and technology that we did now like back in 1915 to be able to say, "Hey, this is for real." But we certainly have those tools now. He was spot-on about that.
8:17
Another piece of evidence, very compelling, was glacial striations and glacial deposits called moraines. So various moraines from ground moraines to end moraines, which are known also as terminal moraines, but basically striations like you see right here. Here's some striations as you're looking in Mount Rainier. Can you see the scraping on the rocks? Well, that's following the path of journey of glaciers. So those kinds of striations exist all throughout the Gondwanaland continents,
8:49
which are the southern continents of Pangaea, and they all travel in very specific directions. And so it's very clear where they originated and where they finished indicating that they were far enough south in latitude that they could create these massive global types of what we call continental ice sheets today. So you have to think about Gondwanaland being far enough south in latitude that it would have been cold enough and wet enough in climate
9:22
that you could have generated continental ice sheets much like we have in Greenland and Antarctica today. So the path of the journey of these ice sheets left behind marks and rocks that are there. They're proof. They are legitimate, hands-on, tangible proof. No circumstantial to it. Another cool set of fossils were pieced as evidence by Wegener, and they're called glossopteris. So I think Glossopteris looks like hemp and if you want to look that up you can. This is it right here.
9:59
But glossopteris exists on all of the Gondwanaland continents; their fossils do. Kind of an important detail because that meant that these continents were in close proximity at a latitude that would allow for the growth of the same type of plant. So as you get to variation and distance in latitude, that just can't be the case. So at some point in the same-age rocks and the same fossils appear in all of these places, indicating that they were once joined.
10:31
Wagner also found some important vertebrate fossils. These particular freshwater reptiles are important because they did not have physiology that would allow them to swim for any great distance. So if you've worked with vertebrates, alive or fossil versions, they have very specific chest cavities, vertebrate paleontology, that either empowers them to be able to travel long distances. Let's say like whales or sharks in water.
11:04
Well these animals don't have that. They're made for short distance and that's it. So they must have lived in something like swamps and lakes that they could travel freely because their fossils are clearly found in South America and Africa. Making them an important type of evidence that these continents were once joined in the timeframe of Pangaea. And I might add the rocks that these fossils are found date back to that time frame.
11:33
In spite of glacial moraine deposits, striations, geometric fit of continents. In spite of the fact that there was glossopteris plant fossils that were on every single continent; all of this compelling evidence, and matching rocks, and in all of these places, the scientific community kind of went, "Well, that's all fine and good, but you don't have a true mechanism that explains why and how continents could move on the Earth's surface."
12:06
Being a scientist, it was a pragmatic process that I could understand them asking. However being on a jury of today, I would have to say he had compelling physical evidence. But new evidence would surface, and it would happen during World War II. So let me explain the significance of World War II. So we all know when Pearl Harbor happened, and basically it was a pivotal moment for the United States to formally announce
12:39
that they would declare war and specifically on Japan, and then you know the rest of the story about that. Well part of all of this involved in the World War II syndrome was we needed to get busy as a nation figuring out where our enemies were hiding their submarines. And so we began mapping the ocean floor and using Magnetometers and other new technology and sonar technology, and we were literally mapping the unknown. Where we could hide our stuff and where would they be hiding theirs.
13:12
So we didn't have a surprise attack like we did at Pearl Harbor. That is a critical piece of how plate tectonics came to be validated. So let us talk about the Father of Seafloor Spreading. Naval Captain Harry Hess. This guy was a big deal and if Wegener could have met him and shook his hand I know he would have because it was the work of Harry Hess that actually validated what we know to be true as continental drift. Although he is the Father of Seafloor Spreading. What did he do?
13:49
During the war he was actually one of those people mapping out the ocean floor, but as he was doing so, he noticed that where they would map certain rock layers, they would move the next time they'd map it and pass back over that same spot. So he had a hypothesis that, "Hmm, the ocean floor must be spreading and moving." He was spot on! So after the war he spent the remainder of his career working on the science to prove his theory of seafloor spreading.
14:21
His data actually proved that there was a long string of volcanically active ocean ridges known as mid-oceanic ridges; MORs. And that these are found in across the world in most every ocean basin, and that these MORs are evidence of the plates moving across the world. So that was a piece that would get validated with one more important element to prove that we'll get to in a minute, that was found as a consequence of World War II also, which is magnetic striping.
14:57
So magnetic stripes; What are they? Why are they important? Basically when molten igneous rock that has any type of mineral that is magnetically inclined. In other words like magnetite or any kind of iron, the mineral atoms will align themselves with wherever magnetic north is at that time. So, you're familiar with polar reversals. So if we have a reverse polarity, those atoms would not arrange themselves towards our current North Pole,
15:33
they would arrange it to where the reversed North Pole would be. So looking in your book, the diagram, this is straight from your book, the description states that the darker stripes represent reverse polarity and that just didn't show up very well in this graphic. So all the sections, the stripes that are labeled "S" with an arrow pointing down represent reverse polarity. And all the ones that have an "N" represent North, or true North as we know it
16:00
with polarity facing the North Pole as we know it today. So why are North and South polarity important for these magnetic stripes? Here's why: Because the atoms in these igneous rocks that are magnetized that will align themselves with magnetic North, whether it's normal North or reversed polarity. They're locked into that rock until it remelts. So they're like a time clock. And that's the case if this is an mid-oceanic ridge where Harry Hess said it was spreading apart,
16:35
lava would come out and actually pour on either side of this particular mid-oceanic ridge. So these stripes should match, right? And as they get older they push away and new lava gets put in their place. So before these Norths could be put into place, see this matching South and this matching South? They do. Not only are the magnetic stripes there, they match in width. And they do until they reach a continental margin where they're either subducted or about to be subducted.
17:10
So the actual oldest oceanic crust exists right in these areas right here where we have some type of ocean floor that's spread from an MOR and is ready to come and be subducted under a continent. This is a really compelling finding and it's really happened because of magnetometers. As they were flying over the oceans in World War II looking for metal in the ocean, like submarines. Shocking that the entire ocean floor basically had iron in it. And so once they started, after the war actually,
17:44
they started doing something called the deep-sea drilling program. This was confirmed by a taking sea cores, like ground cores the ocean floor and analyzing them and sure enough the ocean floor is not a bunch of mud. There's some there, but most of it is igneous mafic rock. And so that was a big shock, we had no idea. So with that came the validation of the age of the ocean floors. Which we assumed were just like the continents, and to our surprise it was not.
18:16
As you look at this animation of a mid-oceanic ridge that was generated from the National Parks Service you can see, let's just say the orange is reverse polarity, and the green is normal polarity. The point is that the stripes match in thickness, and the thickness represents distance away from the spreading center, and the oldest stuff would be, at this point right now would be this one and this one. And eventually they're going to collide with some type of a continental edge,
18:48
and that will be what causes a subduction zone. Something I should point out is the thicker the stripe that you see on either side of the MOR, the faster the spreading rate exists. The thinner they are, the slower those stripes were created. So the movement was in other words the hotspot probably wasn't as hot, so it didn't push the crust as much and make as much lava as quickly as we would see in some places like between the Nazca plate and the South American plate.
19:20
So if you look at the mid-oceanic ridge, it moves turtle-slow, like two to four centimeters a year. As opposed to 17 centimeters a year between the Nazca plate to South America. So very big difference in moving in the magnetic stripes around the world. The end result is important because we're able to map out that ocean, and I'll show that to you in a minute. But you got to be wondering about magnetic reversals, like polar reversals.
19:48
So the last reversal occurred approximately 780,000 years ago and how do we know that? We can document it because those time clocks that exist in magnetic stripes. Until those rocks are re-melted, those igneous rocks act as clocks showing us exactly where magnetic North was and the polarity of those rocks. That's, gosh! That's big stuff there. That's important information that we have and it's all over the ocean floor.
20:15
There's some on continents where we have igneous rocks that have done the same thing. So we've had a lot of polar reversals. It's not like the world's gonna end if we have a polar reversal. 200 have occurred in the past 178 million years. Then we have 33 that happened over the last 25 million years, and 9 that have happened over the last 3.6 million years. So look at that last nine. Humans have been alive, hominids during that timeframe.
20:43
So maybe we didn't have the same technology we do today. Surely technology might have some issues with changing in polarity, but human race will surely be able to survive a change in polarity. As a matter of fact the pole is constantly in adjustment and so that it is not going to be probably an instantaneous process. No one really knows because we've not documented it scientifically to know exactly how it works. We just know it does happen because the evidence is in the magnetic stripes.
21:16
So looking at how the Earth is mapped out now, let's look at the reds represent zero millions of years old at the ocean crust at its age And then you get this stuff that is pink that is right at about 180 million. So we got some that are right on that sliver of 180 million right in here, and just a handful of other places around the world since the actual oldest ocean crust that we have. I might point out this is exactly an important location where rifting is occurring as we speak.
21:50
And that's why it's the oldest stuff, but if you come over here, here's the spreading ridge between the Pacific plate and the Nazca plate. Look at how red that is and yellow. There's nothing in the greens and the blues. So it's very young geologically, we're looking at 50 million years all the way up to 0 million years at these spreading centers. You can see red all the way along the mid-atlantic ridge. You can see another MOR right here and here. So my point being is-
22:16
You see another one right over here because that's where Juan de Fuca is. All of this action going on down here, that's the Cocos plate, and that's creating all kinds of havoc with plate tectonics and all around Central America which is the cause of why the earthquake happened in Haiti as an FYI. All of this to say that magnetic stripes was literally "The Smoking Gun" for figuring and proving that Alfred Wegener was spot-on about his theory of continental drift.
22:49
Plates are moving indeed and we've measured them, we can see them, we can document it, we can show that they've been doing this for quite some time. It's a magical relationship. So World War II, thank you for giving us the scientific kick-start. Not to mention a War that we won, and thank you for any of you who might have served in that war, your parents or your grandparents. My dad served in that war, so I have a strong appreciation for the magnitude of what happened
23:21
and how much life changed as a result of World War II, especially in geology. After World War II, the deep-sea drilling program became an international phenomenon and scientists were basically put on a certain amount of time on the the Glomar Challenger. Which is a series of expeditions on a boat, that was a deep-sea drilling program boat. And they would collect their cores here, sediment cores, and they split them in half
23:55
and the sediment cores would be analyzed and tested for things like magnetic stripes, fossils, fossil fuel deposits, and so forth, And that's how we were able to validate the age of the ocean floor, and determined that it wasn't just made of mud. Matter of fact it was very little of it was mud. Most of it was igneous rock, surprise! We thought, as we first started the deep-sea drilling program that there should have been kilometers full of sediment that had slowly accumulated at the bottom
24:24
of the ocean floor if it was the same age as the continents. That was not the case. It was just a thousand feet at best. So in the ocean where you're far away from any kind of continent, so you're just getting like dead animals that sink to the bottom of the ocean and whatever sediments might be pushed out there via currents. It's accumulating at a very slow rate of 0.3 centimeters every millennium or thousand years. That's turtle slow!
24:56
So that's one reason there's not a whole bunch of mud near our MORs. Matter of fact, it's just the opposite. You have very little sediment accumulation and just a very thick blanketing of igneous rock known as basalt and if you get beneath that it's intrusive counterpart known as gabbro. Well if you're gonna learn about plate tectonics you also have to learn about some of the surprises we found out as we were mapping the ocean floor. Kind of a shocker, Hey! The ocean floor is not flat!
25:28
Some of it is, but the whole thing isn't. So the continental shelf has a lot of importance to geology. That's this section right in here, And this area is an extension of the continent that's submerged underwater. Important because there's a lot of fossil fuel deposits there, and it makes sense because it's not very deep in terms of what geologists think are deep. So I get this question all the time, what is deep in geology?
25:54
Well probably around 800 -ish feet and I put -ish at the end because it's all about where we can no longer sustain large quantities of life, and the amount of light that can actually penetrate into the different zones of the ocean. So shallow marine is anything less than that, and then you get into like very shallow which is gonna be the several hundred feet of water. To me that seems backwards as a diver, because a hundred foot dive is fairly deep
26:25
and so it took me a while to get past that when I got into my graduate work in geology and I was like, "Hmm. Now that seems kind of deep." So continental slope, what's important about that? You get all these sediments that wash off the continents via weathering and erosion. They come and they get on the continental shelf and these deposits have intrinsic value, actually. And then some get picked up by turbidity currents and push down this thing right here,
26:52
which is a very steep angled continental slope. It's such a powerful current, these turbidity currents, that it literally just hollows out this continental slope making deep-sea canyons. And then if you're not at a subduction zone, you'll get what's called a continental rise, which are the deposits from the shelf through the turbidity currents on the slope and they deposit right here. This will be absent if you have a subduction zone.
27:23
After that you're gonna see kind of the flat ocean bottoms and those are called the abyssal Plains. So the abyssal Plains are just part of the story of the ocean floor. There is so much on the ocean floor we just did not know existed, and obviously the case in point would be MORs. You need to know what that stands for: Mid-oceanic ridges. These are the most extensive ocean, or should I say mountain ranges on Earth.
27:49
They're not just because they're in the ocean, they're just the largest mountain range on the Earth. And it's because new crust is being- Ocean crust is being ejected here under the ocean. That's hard to visualize because you're like, "Like how does that look underwater?" But it's making layers of this material that keeps getting pushed back as new lava is brought up to the surface. So these are divergent plate boundaries.
28:13
If you could imagine that this is a fissure eruption. This one's actually in Hawaii. I might suggest to you that that's what it looks like underwater, but probably at a much reduced rate because of the pressure that's there, but it's gonna be basaltic igneous rock like this. Another really important piece of proof came in the late 70s and that was the discovery of deep-sea vents known as black smokers. And these are found at and around mid-oceanic ridges, MORs.
28:47
Well this smoke is not lava. It is certainly volcanic fumes, and it's mixed with dissolved minerals that come from the volcanic process. So black smokers are like a needle in a haystack. They're so small in comparison to the vast size of the ocean floor, that finding them is not as simple as sending a submersible down and, "Woah, hey! You hit it! You found it!" There's a lot of science and expense that goes to finding areas that could potentially be deep sea vents, black smokers.
29:20
When it was discovered was like the last big piece of proof that Wegener was right. That we definitely have continental drift in place and that we do have volcanism. Harry Hess was right about that at the bottom of the ocean floor. So deep sea vents, black smokers, big deal when it comes to a discovery at the bottom of the ocean floor. Well when we did our mapping of the ocean floor a big shock came in that we have these really deep places called ocean trenches
29:53
and they weren't just a little deep, they were like mega deep. Like Marianas Trench deep. They exist wherever you have a subduction zone where one plate is sinking beneath the other, so it makes a big V, like this image right here, in the ocean crust. So these are the steepest, deepest locations on the seabed floor. And they're called deep-sea trenches. That was a discovery primarily because we mapped the ocean floor. So where are these things located?
30:23
Wherever you see the teeth pointing a continent, you'll see a trench here. There'll be trenches all the way through here. This is the Juan de Fuca-Cascadia subduction zone. This is the Aleutian trench subduction zone here. Over here the Philippines' where Marianas would be. Here's the Japan area that caused the big tsunamis when the big earthquake occurred. All of this is related. Here is a plate, ocean plate smashing into another, so that's not subduction,
30:51
but all of this area, the Ring of Fire really should be the ring of subduction and shaking. All of this is subduction right here. New Zealand's a mess by the way, when it comes to being one of the most seismically and geologically active areas in the world. Indonesia, another case in point. So you can see that subduction ocean trenches exist all over the world. And likely that's the way it's been working for, you know millions and billions of years.
31:22
So there are areas where we don't have that situation. We have passive margins. In a minute I'll go back to the map I was just on. Passive margins represent edges of continents that do not have active plate collisions or rifting. So rifting is actually carrying a part of continents like a mid-oceanic ridge would at the bottom of the ocean. So in other words, we have no plate collisions happening. So let me go back to the prior image.
31:52
Let's look at the East Coast of North America and the East Coast of South America. These would be very passive margins. So don't be fooled. There have been very active in the past. Like geologically speaking, hundreds of millions of years ago, but they do not have any current plate collisions. So as soon as they do, let's say this mid-oceanic ridge known as the mid-atlantic ridge pushes the North American plate, and we start getting ocean crust that finally subducts along here.
32:21
This will become an active zone again, but until then it's considered passive. So passive zones do not have plate collisions or rifting that's occurring. So you'll see a pretty healthy continental rise deposits, these deep sea fans here that are on the rise from the submarine canyons on the continental slope right here. So this is a great time to take a short pause. I'd ask you to go get yourself a legitimate beverage, and a snack and come back in a few minutes.
32:58
And we're gonna actually show you an area that has some active plate tectonics going on, and then we're going to talk about plate boundaries, and give you a case study in Hawaii. So I'll see you back in a few. Bye! [silence]
33:26
I'm getting hungry myself, I may have to get a snack too, but welcome back! You're here to learn about some plate tectonics in action and we're gonna go to a place in California. In Northern California to be exact, called Lassen Volcanic field. It's a National Monument and it is a great place to visit, but very geologically active. I am at the Lassen Volcanic field in Northern California, part of the Cascade Range. And a couple of things I'd like to note about this stop:
34:01
First of all is the monitoring device in front of us right here. This is a GPS unit and a seismograph station. So they got a seismometer that measures earthquake movement because this is still a very active system. And they've got these across the park, but this was the one that was the easiest to see and get close to to take a shot of for you guys. My question to you is, why would they be measuring this, and why here?
34:30
I'm at sulfur works in Lassen Volcanic Field and obviously there is a fumarole vent. And the mud pots you see going off down here are pretty fluidy. And of course it stinks like sulfur dioxide, like rotten eggs. One thing I'll make a note of, I'll come back to what you're seeing. I want you to take a look at the ground and notice that it is compromised. We see all those mud cracks. And...
35:11
The reason is because we have almost a sulphuric based acid coming up to the surface where groundwater has mixed with volcanic fumes. So that's what mud pots look like. That's how they behave. This thing can grow in size. And I would say it would not be the wisest choice to be walking on ground t that has texture or surface like this does. People do sillier things. There's signs that says not to, but there's a reason why it's there. I want to focus in on this stream.
35:49
And want you to note the color that you see is kind of a rusty orange. That's not the color of the water of the creeks around here. There's very clear beautiful water; that is not. That's coming from the mixture of materials that are reacting to the material that's in the volcanic tuff, or ash deposit that you see here. The silica rich material, which is one of the necessary elements for forming things like geysers.
36:22
I don't see any evidence of geysers here, but certainly do you see evidence of thermal features. Based on what I see in terms of the color of volcanic material. I would say we're looking at a felsic, or a high intermediate silica-type volcano. Welcome to the subway. This is a volcanic lava tube, And you can see the cap is still in place on the lava tube. A lava tube forms as lava travels when it's hot, out of a volcano and the top portion of it begins to solidify
36:58
and keeps the material harden underneath it. Many times the roofs collapse. Until they do they make a really good insulated cave, and I'm fixing to walk into Subway Cave. So this is part of the Lassen Volcanic field, which is the part of the Cascadia range where Juan de Fuca plate has been subducting under the North American plate. Welcome to Subway cave! As I enter into the Subway Cave I will not be able to photograph considering it's pitch black in there.
37:31
But I wanted you to see what the action or cave looks like. Keep in mind this was a lava tube where lava traveled back when this thing erupted.
37:48
So here we are at the end of the cave. It's about 1/3 mile hike. And you can see that we have another opening for the lava tube where this rubble here represents the collapsed lava tube roof. And it is now exposed for people to walk through. It's kind of a rugged walk. I would say the average height from top to bottom as we walked through it was probably 10-12 feet. Here it may be a much as 20 feet.
38:16
But you have to imagine that there was lava running through this thing back when it was active. So say goodbye to Subway Cave.
38:30
I even have a motto, Animal momento from Lassen called Lassen! And it's a little stuffed squirrel from the cute little squirrels and chipmunks they have there. But I have fond memories of going to the park because it was very much an active location. So you saw cinder cone volcanoes, you saw a composite volcano, like Mount St. Helens that even had a lava dome on the side of it. You also saw thermal activity with the hot springs, and mud pots, and fumaroles.
39:05
You saw what is called a kind of plug volcano, volcanic dome feature that is very unique, very dangerous type of volcano. And then you saw a shield volcano, what the heck is up with that? Shield volcanoes typically form out in the ocean and this one actually drifted on a plate just like Alfred Wegener said, and connected during a subduction event, and glued on, accreted onto our continent. It's a kind of a neat place. A case study and certainly that plate tectonics is real and active.
39:40
There are three types of plate boundaries. Divergent which pulls apart. "Di" means move apart, like divorce. Convergent means they push together, and then transform means that they move side-to-side. All three of these can happen in regions. Like New Zealand has a combination of all three things happening at different locations within the islands that they have but they have a dominance in convergent plate boundaries. A very, very busy place. So we're gonna look at all of these,
40:18
and then talk about how they are similar, and how they are different. But let's talk about divergent plate boundaries. So to be kind of transparent here, to have the really awesome geology stuff like subduction zones, you've got to have divergent plate boundaries on the other side of that somewhere. And the case in point would be Juan de Fuca. So that's separating away from the Pacific plate and being pushed into the North American plate.
40:46
Same things happening with the Nazca plate, and it's smashing into South America. And when this happens, amazing geology stuff occurs. So there are two different types of divergent plate boundaries, and you need to be able to differentiate between the two. There are MORs; stands for mid-oceanic ridge. Oceanic being the key word. So ocean plates pull apart and that's because of tension like a rubberband being pulled.
41:14
That's caused by heat sources like hot spots that weaken and cause the crust to pull apart. Well the same thing can happen when we have rift zones, which are continental plates that do the same exact thing. So they pull apart because of tension, but on a continent and when that happens you're gonna get a string of volcanoes on the continent where it's weakening. So a great example would be the great African Rift Zone on East Africa.
41:46
That is a string of volcanoes that is a result of the continent being pulled apart. So ultimately if it succeeds, you're gonna have a giant Madagascar because it's exactly the same kind of process. Same thing with the Red Sea. Ultimately the Red Sea may completely pull apart and when it does it's a brand new mid-oceanic ridge. So if a rift zone fails it's called a failed rift, and you'll just have kind of a crack in separation point
42:20
and probably lots of volcanism that occurs until the hot spot dissipates. We have a region in North America that is a rift zone that moves very very slow. And it's in New Mexico area and some people may even consider this a failed rift, but it's still moving today. So I'm considering it active. And if you think about areas, all continents like Pangaea, when it came together, Alfred Wegener's supercontinent, the only way it could split apart is via rifting.
42:50
So rifting is a natural part of plate tectonics. There's a rift zone I've been to called Iceland, and Iceland sits there in the Northern Atlantic. It's one of few places on the planet where you can actually see a divergent boundary at the surface. And it is a rift zone that is becoming an MOR. So here is a look at Iceland and you can see that the- here's your MOR, but you're not- This is on two parts of a continent. You've got the Eurasian plate here and the North American plate here.
43:25
So on this side, this is the North American plate. This is the Eurasian plate because I'm facing North in this picture and it's spreading apart. Well there were some places that I could actually touch my hands if I did a full wingspan there. Other places it was much larger than that. So depending on where you were on the island, and to how fast the movement had gone. But this all occurred because of a hotspot that had upwelled from the asthenosphere into the lithosphere
43:54
causing Iceland to pull apart. So I cannot underscore the importance of rifting. It is how continents got pulled apart when Pangaea came together. Subsequently we will have other plate boundaries that bring a future supercontinent together and that's going to be called Pangaea Ultima. I promise you I'm not making that up, but that's the new supercontinent that should form at about 200 million years. So here we are in the Permian when they all came together. Here's Triassic.
44:27
You can see the ocean basins are opening and by Cretaceous, you can actually see the Atlantic is opening here. You definitely have separation of the Southern continents. In present day they've all moved to their respective locations. So plates continue to move. And they're going to continue to do it as long as we have a core that produces that radioactive decay heat that creates those convection currents.
44:54
So convergent plate boundaries crossed together, and they happen because of compression. Typically two plates collide because one plate has been pushed into another plate, a nearby plate by a divergent plate boundary. Case in point, it'd be if this was the Juan de Fuca area. Here's Pacific plate. This is Juan De Fuca. It's mushing into North America. Same scenario if you're looking at the Nazca plate of South America.
45:23
So here's the Pacific plate, here's the Nazca plate, and it's pushing into here which would be South America. The key is how much heat is being generated at that hot spot. That's gonna be an important element as to how fast or slow that MOR exists, but remember convergent plates are this relationship right here, where two plates collide. The most common one is called a subduction zone and this involves typically an oceanic plate colliding with the continental plate.
45:51
And the reason that this is important is oceanic plates are more dense than continental plates because they contain a higher amount of ore like iron. And so specifically iron because they're mafic. And so they just have a little bit more density, and you'll learn more about that later on. And as they do they sink, some of it may stick on and this accretionary wedge right here is like ocean sediments that got squished up
46:18
when the collision occurred and some of it may stick on if you had some island arcs, they may stick on here, and add some continental mass and the rest gets subducted. And then as it gets deep enough it melts, and fuels up volcanoes. Typically you have a series of volcanic areas, regions that are close to the shoreline. And if you go to the Pacific Northwest, if you go to Northern California, just where I was showing you with Lassen Volcanic field,
46:48
that's the result of a subduction zone from the Cascadia subduction area Juan de Fuca under North America. Sometimes we have two ocean plates that collide. You may have small amount of subduction, but typically ocean plates are very similar in their density, but they will create volcanism in the form of island arcs. And so these volcanic island arcs are all over the ocean basins around the world, which is a surprise because we knew they existed, but we just didn't know how they got there.
47:17
You know, did they float out there? It turns out that they actually grow from the bottom of the ocean. Then we have another situation where we have convergent zones of two continents that smashed together. So continents are kind of like those marshmallows I was talking about when we were discussing density of plates and Dynamo Earth. They push up just like if you had a head-on collision with two vehicles. So they produced the tallest elevation mountains in the world,
47:45
not tallest total relief, but tallest elevation like the Himalayas. And these areas are gonna be highly deformed. Lots of folding and faulting and rock deformation, so they're kind of a mess. So I'll give you an example. If you look along Pakistan and that region, there's lots of earthquakes that happen in those regions that are pretty serious, and it's a result of that collision of India with Eurasia. So that's exactly what causes that.
48:17
So we're going to cover the very last of the plate boundaries and then move into our case study. Transform plate boundaries cannot be underestimated. There are lots of them along mid-oceanic ridges as the plates move and diverge away. They kind of get offset and they make lateral faults. Which are strike-slip faults, which is what is shown right here. And a very famous place to see a side-by-side plate movement is along the San Andreas Fault.
48:50
I'd like to point out the San Andreas extends into the Pacific Ocean but has nothing to do with the volcanoes up here along Juan De Fuca. That region is a subduction zone. So starting here in California all the way to Southern California down into Mexico, this whole San Andreas Fault extends for about 800 miles. And along that section, North America is moving in a Southeasterly direction. Well this Pacific plate is moving in a Northwesterly direction,
49:22
and that's about three or four centimetres- ish a year. If that didn't sound like much, if you put that over a million years, you can relocate a house. And certainly we've had stress build-up along these fault zones. And every so often we have some kind of a large earthquake there. And unfortunately it's a highly populated area, so it has potential to be a problem. So what's the driving force of plate tectonics?
49:49
Let's link back to Dynamo Earth and talk about the asthenosphere and convection currents. Remember convection is that heat that is moving in the asthenosphere, but that heat comes from the core. And so as the core releases that radioactive decay heat that allows the inner earth, that heat to rise and get into the asthenosphere, and that convection to move it, and then mantle plumes evolve. And this is that simplistic model of convection I was talking about earlier, your typical-
50:24
And this is the way it looks, very simple. What research has shown in the literature, is it's, they're very complex. But nevertheless these hotspots come up, and they fuel up, and they separate this crust. Like here's a mid-oceanic ridge right here. So think about how that's going on, and eventually if we lose our heat source from in here, plate tectonics will slowly die off. So to be transparent it has been slowly changing since the inception of Earth.
50:58
So in the beginning of the Earth there was a period of time where the core was releasing immense amount of heat and producing very rapid plate movements and development of plate material. So it slowed down. And it's not stopped, of course, because we know the plates are moving. We measure them and we can do that with GIS technology today, satellite imagery. There's lots of things we can do to see that we have a very active plate tectonics.
51:26
But it was more active at one point in geologic past. There will become a point in the future where it slows down and becomes dormant. That moves us into our case study. So I've been to Hawaii multiple times and I don't think I'll ever get tired of it. It's just one of those places that I love and not just because of the geology but the people, and the location, and how isolated it is. But it is a geologic wonder. But it's not an isolated case,
52:00
there's many other island arcs that are just like Hawaii that formed in the similar way. So this is not at a transform plate boundary. It is not at a convergent plate boundary. It is not at a divergent plate boundary. Instead we got a hotspot called the Pacific Hawaiian hotspot sitting right out there in the middle of the Pacific plate. Right here to be exact. And that hotspot has been generating a slew of volcanoes, to be exact, I'm just following my mouse here.
52:36
Makes an abrupt turn there and goes all the way up to the Aleutian trench. It's been doing it for over 82 million years. "How do you know that Elaine? How do you know it's been doing it for 82 million years?" We have some proof. We're gonna get to that. So Alfred Wegener knew that continental drift occurred. The Hawaiian island chain is one of many pieces of proof that shows that it actually is still occurring today.
53:05
So J. Tuzo Wilson is the father of hot spots, and he's done extensive work on determining that there were hot spots around the world that generated extensive volcanism and prolonged volcanism, like the Pacific Hawaiian hotspot. And I want to point out that Kauai over here, O'ahu, this is gonna be Moloka'i, Lanai, Maui, Hawaii. They've all been on the hot spot at some point. Hawaii this section of it right here is currently on the hot spot. And this new Sea Mount is growing on the hot spot.
53:47
So as the plate continues to drift this direction, Hawaii will come off, and Loihi will become a new brand-new volcanic island. Well let's go back one. Well Loihi right here. This is your small little island chain. Midway is about right here, important to World War II, and then of course we have a lot of underwater Seamounts; many of them guyots, which you'll learn about in a minute. All the way up here to a subduction zone at the Aleutian trench.
54:19
That's a huge amount of distance, and every single one of those Seamounts, whether they're underwater and have been off of it for millions of years, or they're like Loihi growing on it right now. They've all passed over the same hot spot, and generated an Island. Volcanic seamounts are caused by hot spots. One thing to note is if this is the bottom of the ocean down here that's where they start forming,
54:47
and they grow and grow and grow until they puncture the ocean surface and become an aerial island. What I mean by aerial is they're touching the air, so they're not submerged. That happens rapidly in the case of the Hawaiian hotspot. For example this Island right here, which is Hawaii is less than a million years old. And that it grew up in like seven or eight hundred thousand years from the bottom of the ocean floor. So that's repetitive volcanism. So that's what a hotspot is.
55:19
It's an area that has prolonged volcanism on Earth because of this crustal heating that comes from hotspots, magma plumes. That's what a hot spot is. Remember there's about 40 to 50 of them around the world. So remember that Seamounts volcanic islands, grew up on the bottom of the ocean floor. They don't just like float. They're like attached to crust. So if this is Hawaii right now, the big island, this is going to be an older Seamount.
55:48
Well currently we have some islands in between; the closest island would be Maui, then O'ahu, and then a group of islands all the way over to Kauai. And as the plates drift, the Continental drifting occurs, the whole the island that's exposed will get weathered down and erode to sea level, and then ultimately go below sea level, it's an older Seamount. And then it becomes a Guyot and Guyots are characteristic by having flatter top.
56:19
So when you see older seamounts and those were many that are passed midway in the Hawaiian Emperor seamount chain. They are flat like that. That was a discovery that was determined, new to scientific information during World War II, when we're mapping the ocean floor. Guyots were like, "What's this? What are seamounts? These are new things. We didn't think they were there and they are there." To be transparent here's the current Island of Hawaii generating lava, and so forth right now.
56:55
Every one of these islands whether they're submerged or above water, here's the midway point, and then we come all the way up to the Aleutian trench. Every single one of these volcanic seamounts formed in exactly the same place, right where the arrow points to Hawaii. So you may wonder what's the deal with that abrupt change and plate direction at Midway? Good question. At some point there was a plate collision of India with Eurasia.
57:25
That is thought to be in tune with causing multiple plates to kind of displace and move in different directions including the Pacific plate. So, how old is this hotspot? Well we know it's at least 82 million years old, and how the heck could we possibly know that? Has to do with data collected from under water seamounts right there. So let's find out about that. This cluster of islands from Hawaii all the way to Kauai are the main islands.
57:59
So there's several islands around Maui that are important. We'll get to them in a minute that are smaller, but the point is that this image shows you the vertical drop all the way down to the ocean floor. Remember I told you these things grow up really fast, like too fast, so they're not very stable. So they break apart and mass waste, and huge landslides. What I mean huge, they like totally break apart. They're very scary and when this happens they leave Islands in a state of array.
58:33
There's marks left behind where there are steep ridges, and I'll talk about that in just a little bit. When we're doing the case study of Hawaii, we need to talk about an important cluster of Islands that used to be joined. This section right in here. This is Mount Maui, this is Moloka'i, this is lanai, and this is a private island right here. They all used to be one. And this is kind of a three-dimensional depth map to show you this is just the deep ocean.
59:05
This is right along the coastlines, and they progressively get deeper. What is really crazy is when this thing was joined at the hip, it was called Maui Lui. So the main island that we call Maui today, it's just it's an incomplete Island. It used to be parts but in connected to these. But what happened was that it catastrophically broke apart about 200,000 years ago. And it broke apart because these islands grow from the bottom of the ocean floor
59:35
all the way up to their summits in less than a million years. And they're just one layer, upon another layer of lava and they are just not structurally sound. And when they break apart they slough off in mass concentration. So a big side of the island literally [bam], just come straight off. And as I took a ferry ride from Maui to look at Lanai, and also to go to Moloka'i. When I reach Moloka'i, in particular this coastline right here. So we took the ferry from here to here.
1:00:10
I was so struck by the fact that there was these scarred steep embankments where you could just see big sections of the island fell off. And when we got there, I knew about the tsunami deposits that were on Moloka'i but I went and saw them and it was rather stunning because when this happened these islands broke apart and literally fell into the ocean displacing water creating just huge enormous, oversized mega tsunamis. So if that were to happen today and it likely will.
1:00:44
It will likely happen over here, right along this section of the active Island of Hawaii. That will be very bad for the people who live in populated areas or even on the Islands period. So I have a friend who I've taken a few classes with that's a geology person. He leads some tours and geology stuff over there and I've taken a couple of his courses, and he lives right here. And he says, "You know if Hawaii breaks apart like Maui Lui did, I'm just gonna go get on the top of my deck..."
1:01:17
Because he has a three story beach house, and he said, "I'm just gonna pop one open and have a cold one, and sit there and wait for the tsunami wave to get there in about ten minutes because when it does, it's gonna be my last breath unless I have a helicopter and get into the air. And then there's gonna be nothing left for me to land on. So either way it's a bad deal." And it really will be because Maui Lui was just a precursor,
1:01:41
and that there's evidence all over the ocean floor of where these deposits traveled in and you can with modeling, computer modeling, they can determine how fast that's happened. And it was a rapid instantaneous mass wasting event. So if it were to happen today where this new Island is growing called Lo'ihi. And it's going up against Kilauea in Hawaii. Kilauea is slipping and it's already being documented that it's slipping off. So it's just a matter of when, it's not a matter of if.
1:02:15
Shield volcanoes formed because they make one layer at a time, and they're constantly erupting at the bottom of the ocean floor. So one important thing that happens with them is they make little blobs of lava that look like pillow shapes. They're called pillow basalts, we'll get to them in just a minute, And you can find them all the way up the sides of these volcanoes, all the way up into the surface where water actually drains off the surface from lava tubes or lava flows.
1:02:45
So we're going to learn about the oldest seamount, and the youngest seamount, and the Hawaiian Emperor seamount chain. Meiji, right here is the oldest seamount. And it's waiting to be subducted at the Aleutian trench. So I mentioned those pillow basalts, and those pillow basalts are up and down the sides of all of these volcanic seamounts; many of them guyots, as I mentioned with the flat tops. And this particular seamount we have taken samples.
1:03:18
Meaning scientists, all the way at the bottom, and they've aged dated to 82 million years of age. So just theoretically speaking, it is possible that there have been previous seamounts that have already been subducted. So that's why I'm saying at least 82 million years old the hot spot has been. It's very possible it's been longer than that. Once this particular seamount is gone, the next one will take its place, and it will continue to move as continental drift occurs.
1:03:52
So this particular seamount has just a few million years before it's gone and it's left us, and there's no proof of it that it ever existed because it'll get recycled into the mantle, just as the rock cycle works. Loihi is the most new of the volcanic seamounts. It hasn't reached and touched the ocean surface yet, and become an island, but it's fixing to. Probably in about another hundred thousand years, we're gonna have an island right next door to Hawaii.
1:04:22
And it is currently active, very active. It's been growing, literally. It's about 400,000 years old. And it literally has 3,000 feet before it reaches the surface of the ocean. So it is not very far from becoming an Island. So I want you to kind of look at the various different, here's Mauna Kea which is the highest point in Hawaii, Mauna Loa which is the absolute biggest of all the volcanoes in the world, Kilauea, and then you have several others.
1:04:51
There's five big giant volcanoes that currently make up Hawaii and then Loihi would make the sixth. And so it's pushing up against Kilauea. This is where that mass wasting could actually occur. So I wanted to point that out because, gee we got activity! and Hawaii is made up of five of these monster volcanoes. It is just an accident waiting to fall apart. Another term you need to be familiar with is "total relief." Test question for sure.
1:05:24
Shield volcanoes contain the highest total relief of any structure on Earth. And that goes back to being growing from the bottom of the ocean floor, becoming a seamount that actually punctures the ocean surface and then has a summit at the top. While it may not have the total elevation award, like we would see in the Himalayas Mount Everest, it certainly has the total relief from the base to its summit. Because if you look at Mount Everest,
1:05:52
it starts the base of it well above thousands of feet above sea level. And then it continues up to its peak. Well when you're looking at something like Mauna Loa or Mauna Kea, these things are so big! They are much larger these giant shield volcanoes than Mount Everest ever will be. So that's what total relief means, from the bottom of the ocean floor all the way to its summit. So they're much larger than total elevation.
1:06:23
So we're going to look at a couple of the famous volcanoes in Hawaii and this is Mauna Loa. It means long mountain in Hawaiian, and I can tell you I've driven over it. I've rented a jeep and drove from one side of the island to the other when I took a course, and boy it was snowy up there at the top, cold, and then you get back down to sea level in the same day. It's kind of crazy. This is Mauna Kea, and one day I took a tour all the way from the bottom of it at sea level,
1:06:54
all the way up to the highest point where we hiked the highest summit. Right where the Keck Observatory exists. So on top of Mauna Kea where a number of cinder cone volcanoes which are very simple volcanoes, the simplest type. And they represented short-lived volcanism that occurred after the building of the island occurred. It's a little bit more explosive than the actual building of the island. Here's a cinder cone, this is the high point of Mauna Kea.
1:07:21
I've hiked there and can tell you is pretty cool. This is the Keck Observatory, and then all these deposits on the ground are not just lava, but they are glacial deposits! Who would have guessed that Mauna Kea has glacial deposits? Not to mention glacial striations. So during the last ice age this became home to a rather impressive set of glaciers, valley glaciers. Then that moves us into the current, most active of all of the volcanoes called Kilauea, which means "spewing" in Hawaiian.
1:07:55
And this is the Pu'u'O'o vent. This is a classic look at a volcanic fountain, lava fountain, and you can see the black material that's the basalt lava that is generating. This is the actual caldera. Remember learning about calderas earlier? There was a reason to learn about them. Below Halema'uma'u caldera, which is this thing right here, sits the hot spot literally more than 30 miles beneath the surface. Deeper than that actually.
1:08:31
Point being is, this is the direct activity; It's often filled with lava, so it's a lava lake. You can actually see there's a secondary caldera here. And this you can see evidence here of sulfur deposits. If this thing was producing thermal activity-- So the caldera is the actual center where the visitor center is located for the volcano National Park in Hawaii. And it sits on Kilauea Volcano. So you're looking at this section right here.
1:09:03
And as you look at this area, I had been there when it got so bad with the activity that they shut access to the rim because of deposits, pyroclastic deposits being spewed out. So it can be kind of dangerous. So what are some things you could expect to see if you went to Hawaii Volcanoes National Park? You'd see spider ramparts and fissures, for example this is a spatter rampart which is like a big fissure opening and it's active and you can see all the globby stuff.
1:09:37
By the way there's a geologist and gear to test that particular fissure. And this is a spatter cone that, same thing in Hawaii. The red actually is not because it's hot; it's because it's oxidized. Very quickly that breaks down lava in a humid area like salt water in Hawaii. But this had this kind of stuff coming out of it just literally probably tens of years before this occurred. Because this was close to an area that had been hit by lava within the decade before I got there.
1:10:13
Lava tubes are another very important feature, and I mentioned them several times in the course already. So they help insulate the lava right at the surface until it can drain into the ocean, and that creates a hydro volcanic eruption, which is exactly that picture I showed you. And here's that caldera, Sso how far is it from here to here? It's a good more than 10 miles, I think it's really more than 15 if my memory serves me right, but it's a ways. This is more like 10 miles here.
1:10:43
So it's a distance to travel and those lava tubes really insulate the lava to help it stay molten to get to the ocean. So the lava tubes allow for these vents that are on Kilauea to keep that lava molten all the way to the ocean. And if it does it will have a hydro volcanic eruption and create that black sand beach, which is actually made of volcanic glass or obsidian. So the top of it will solidify allowing an insulation moment to occur, keeping it molten longer.
1:11:15
And this is that hydro volcanic eruption where lava tubes and lava flows brought lava all the way to the Pacific Ocean. And it's super cooled that lava and helped create- Here's some new black sand beaches right here that are being formed. This is how the Island grows. So as this volcanism occurs, more real estate is added to the particular island, Now this right here, this area was a whole subdivision. I need to point that out to you, and it was houses buried in this.
1:11:48
So while people real-estate may be in danger, the Islands growth is happening, but keep in mind it is unstable, unstructurally sound growth which means it could be subject to mass wasting. I want to be sure you're clear on how black sand beaches are different than regular sand that's just black. True black sand beaches are made from lava that super cools in the ocean and becomes obsidian. And so it's broken up volcanic glass.
1:12:19
You can walk on it, it isn't going to hurt you because the wave actions rounded that sand grain. And but it can get kind of hot, and it gets pretty hot during the day, but they're really beautiful and unusual, and that's why I have a handful of it right here to show you that it's very coarse-grained. I have some in my classroom on campus if you want to come feel it one day and see it because it's rather remarkable to touch. So I promised you we'd look at pillow basalts!
1:12:48
And pillow basalts are really fascinating. So I'm gonna ask you to Google search active pillow basalts. There's some tour features or guides in Hawaii that have some footage of divers photographing pillow basalts because I don't want to copyright a problem by copying their work. So I want you to go just google it, and look it up. But once you see how they form; its these structures are forming. So they're called pillows because they look like big giant pillows,
1:13:20
and when the water hits the ocean or you got lava at the bottom of the ocean, that's you know as it's- the volcano is erupting as it's moving from the bottom of the ocean upwards. These things literally pour out and as they cool, they make a pillow shape feature and then they more of them kind of pull out or billow out of the pillow to make more of the same. And that video shows it really, really well. There are multiple videos out there, but this one in particular is really good.
1:13:52
Here's what pillow basalts look like on land. So this is in, right out of Hilo on the East coast of Hawaii. And this tells me something. And if you see them anywhere in the world, they should tell you the same thing. They should tell you that ancient volcanism once existed near a water body because that's what pillow basalts are. They are lava that came in contact with ocean water and made these pillows structures. So this was underwater at some point. So there was underwater volcanism
1:14:24
that allowed these to form. So sea level is at a different place now than it was when these were formed. That helps me understand if I find these on land. Like you can find pillow basalts right in the middle of the Petrified Forest and Painted Desert. And that is an indicator that there was some type of underwater volcanism that occurred in Arizona at that time. So if you find these in China, or you find them in somewhere like in Antarctica,
1:14:50
they all represent the same way that they were made; the present is the key to the past. So I'm going to end today with a nature moment. I know it's been a lot of information, but plate tectonics is the foundation piece of our course. Remember you need to come back for section 4 over minerals. Let's watch our nature moment, and I'll see you back for our next section. Bye!
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