Audio transcription of earth science lecture with approximately 80% accuracy

Understanding Earth's Crust: Oceanic and Continental

We talked about two different types of crust, oceanic and continental crust. One is old. That would be continental crust. The stuff we're standing on or one is new oceanic crust because it is constantly being subducted and recycled into the mantle. Now, we'll also be on the quiz.

Plate Boundaries: Convergent, Divergent, and Transform

There are two three types of plate boundaries and talked about convergent, divergent and transform boundaries. Here are the plates that we are aware of. We notice that earthquakes tend to concentrate around plates and where they meet other plates, both divergent and convergent and transform boundaries will produce earthquakes.

Earthquake Zones and Trenches

Typically, and someone said this in the other class on the quiz trenches, so like the Mariana Trench, the Challenger deep do not occur around divergent zones. You might think they would because you have like the seafloor spreading. And so you might get like a trench. Those typically actually create rift valleys, the spreading those. Also, they create mid-ocean ridges like the mid-Atlantic ridge.

The Formation of the Himalayas

But the the trenches, as we know them, typically occur around subduction zones. And this is also where enormous earthquakes can be generated from. I think I left off on strike slip boundaries. Those are just the ones that grind against each other horizontally. And they produce earthquakes through that fashion where they just get stuck on each other until the pressure is enough to overcome the geo geology that is preventing it from snapping.

The Mid-Atlantic Ridge: An Example of Seafloor Spreading

We watched some earthquake videos, talked about the mid-Atlantic ridge. It's the longest ocean or mountain range in the world on the planet, spreading it about an inch a year. We know that it is spreading because we have found volcanic rock many hundreds of miles from the mid-Atlantic ridge itself. And that can only be explained by a spreading behavior. We can also see this spreading occur in Iceland, where it is happening above ground.

Convergent Boundaries and Mountain Formation

Iceland is very active and this is where we left off. So convergent boundaries or those boundaries of which two plates collide. These are known as subduction zones, and we have a very good example of one happening right now with the Indian subcontinent colliding with the Eurasian continent, creating the Himalayan mountain range.

Tracking Plate Movement with GPS

And as you can see, we actually know the direction that it is moving. We can place a little GPS puck, if you will, on the ground, affix it into the ground, you know, like stick it in the ground and come back a year later and track where it has moved over the course of a year.

The Impact of Continental Collision on Climate and Geography

And in this case, we notice that the Indian subcontinent is moving into the Eurasian continent in a northeast direction at about 30 to 2. Maybe it looks like in some cases 50 millimeters a year. So it's not substantial because we're at a millimeter scale here, but it is moving. And many of you have heard that Mt. Everest is growing at some amount of inches per year, and that is because of this collision.

Geological Evidence of Ancient Continental Configurations

This happened many, many millions of years ago, and it completely transformed the landscape even in this picture. And we talked about this when we talked about rain shadows. Prior to this, without a mountain range, this area could have been very lush and green. But once the continent collided or the two continents collided, rather, and we began to build this mountain range, we then got a range shadow that basically starves the Tibetan plateau of moisture and turned it into a very arid plateau, which is what you can see here.

Satellite Imagery and Geological Studies

It's just brown compared to the very tropical looking greenery of the Indian subcontinent. This is out of order. So this is what a high rise satellite image looks like on one end. You see very green, lush terrain. And then it is followed by essentially rain starved, arid desert of the Tibetan Tibetan plateau.

The Legacy of Pangea and Fossil Evidence

And these indeed, are the Himalayas where you get where Mount Everest resides. So it started about 70 million years ago, and it wasn't always in its current configuration. Again, these are like paper plates floating on a pool or on a bat on top of water. They just kind of errant move around. They can twist, they can turn. And at some point, when it collided between 50 million years ago and today, it reconfigured in its current its current configuration.

Forensic Geology: Uncovering Earth's Past

And you can see the distinct outline of where the Himalayan mountain range occurs is right along what we believe the shape of the Indian subcontinent would have been. Now, how do we know this? We can actually do coring samples, get coring samples, and we can find types of geology at the top or not necessarily at the top, but high up in the Himalayas, we can find geology that matches geology that occurs maybe lower on into the Indian subcontinent.

The Rocky Mountains: A Result of Plate Collision

So we wouldn't expect some of this geology to occur here. But what this is telling us, and it's pointing to this study area, the legacy epic for ERA. I need to look that up again. We are finding geology from that time that dates back to that time. We radiocarbon date it. It's at the very top of this mountain where as you get more recent geology here at the at the valley floor from the Pliocene and Pleistocene epics, we are in the Miocene technically.

The Role of Mountains in Shaping Weather and Climate

But what this is illustrating is here we have new Iraq, whereas up here we have much older rock, which helps us date when this collision occurred. And of course, this is Mt. Everest. I've been reading a lot about Mount Everest and how it's super littered with litter, but also bodies everywhere, people who have died trying to get up. And I don't know why anyone would want to do this. I guess it's to say that you did. I don't understand it. It just seems so crazy to me.

The Significance of Plate Movement in Geology

Again, we have evidence of plate movement. I'm not going to go over that one, but they are called ovulate. So if you want to look it up, you are welcome to. Essentially, we can find pieces of oceanic crust and on continental crust in places like California, New Guinea, Cyprus, the Himalayas and Newfoundland, which tells us that there is plate movement occurring, how would we find dense oceanic crust on top of continental crust or mixed with continental crust except by some movement?

Understanding Plate Tectonics Through Geological Evidence

And so this is the type of thing that you see is you can get oceanic crust. It's an event called abduction instead of subduction, where maybe the continental lithosphere, for whatever reason, is subducted under a light oceanic lithosphere, in other words, and then you

November 12, 2023 — Roger Sarkis

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