4.C.4 The Rock Cycle

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來自 University of Illinois at Urbana-Champaign 的課程

Planet Earth...and You!

23 個評分

University of Illinois at Urbana-Champaign

Planet Earth...and You!

23 個評分

Earthquakes, volcanoes, mountain building, ice ages, landslides, floods, life evolution, plate motions—all of these phenomena have interacted over the vast expanses of deep time to sculpt the dynamic planet that we live on today. Planet Earth presents an overview of several aspects of our home, from a geological perspective. We begin with earthquakes—what they are, what causes them, what effects they have, and what we can do about them. We will emphasize that plate tectonics—the grand unifying theory of geology—explains how the map of our planet's surface has changed radically over geologic time, and why present-day geologic activity—including a variety of devastating natural disasters such as earthquakes—occur where they do. We consider volcanoes, types of eruptions, and typical rocks found there. Finally, we will delve into the processes that produce the energy and mineral resources that modern society depends on, to help understand the context of the environment and sustainability challenges that we will face in the future.

從本節課中

Week 4: Rocks and Mineral Resources

As part of the Week 4 Assignment, you will take a close look at your daily surroundings to identify Earth resources. The video lectures for the week examine various aspects of finding, extracting, and using resources such as metals and stones. For the lab, you will utilize Google Earth to examine several mining sites around the world. In the discussion, you will weigh the pros and cons of mining operations, as many communities have had to do already. This week also includes peer grading discussions, as explained on the How Graded Discussions Work page. Finally, we provide an optional assignment for those who would like to identify some common minerals.

4.C.1 How Rocks Can Change11:05

4.C.2 Metamorphic Rocks Part 18:07

4.C.3 Metamorphic Rocks Part 27:49

4.C.4 The Rock Cycle3:57

與講師見面

Dr. Stephen Marshak
Professor and Director of the School of Earth, Society, and Environment
Department of Geology
Dr. Eileen Herrstrom
Lecturer
Geology

[SOUND]

[MUSIC]

We're going to finish this discussion of how rocks change by pointing out that on

our dynamic planet, subject to the activity of plate tectonic,

subject to weathering reactions of the surface, subject to gravity and

landslides and river steam transport and burial and new volcanic activity and so

forth, rocks can change over time.

This overall change that can take place is known as the rock cycle.

Let's look at an example.

Imagine that you have a melt that forms in the mantle and rises up into the crust.

That magma, if it cools,

will form an igneous rock, the first step in the rock cycle.

Now let's imagine later on, the rock over the top's been eroded away and

that igneous rock has been subjected to weathering.

It may break up and form sediment that can then get transported and

buried elsewhere in a depositional environment and

forms ultimately into sedimentary rock, another step in the rock cycle.

Now if that sedimentary rock ends up on the edge of a continent that gets

over thrust by another continent during continental collision, it ends up at great

depth in the Earth and undergoes metamorphism to become a metamorphic rock.

Notice that during this process, atoms that were originally in the minerals of

the igneous rock are ending up in class of sediment and

later in the metamorphic mineral submerge.

In other words, atoms are moving among different minerals,

different locations as a consequence of the rock cycle.

Now there's some caveats to this.

You can go straight from metamorphic to igneous if you have the metamorphic rock

buried so deeply that it starts to melt, forms magma, and rises in the crust.

Or you can have uplift and exposure of the metamorphic rock, so

the metamorphic rock transforms into sediment.

In fact, you can have sedimentary rocks uplifted and

broken apart to form new sediment that then forms another sedimentary rock.

So there are many different paths and roots through the rock cycle.

But the rock cycle exists on our planet because of how dynamic our planet is.

We don't have a rock cycle on the moon.

There's sediment on the surface formed from

impacts of meteorites over billions of years.

But that sediment is never forming into sedimentary rock, and

it's never being carried down deeply enough to form metamorphic rock.

And for at least the last few billion years,

there has not been igneous activity forming new igneous rocks on the moon.

It's just sitting there, static.

Now, I'm going to finish this discussion with one last topic.

And that is how do we get rocks that were formed deep in the Earth up and

exposed to the surface of the Earth?

Well, this process is called exhumation, and there are two components to it.

First, we have uplift.

Uplift may happen during mountain building processes,

because the rock is being squeezed together horizontally, and

therefore is rising vertically, or because one rock is being thrust over another.

In any case, we can have tectonic phenomena that lead to the uplift of rock,

bringing it up towards the surface.

While this is happening, at the surface, weathering processes are taking place.

We can have wind blowing rock away.

We can have streams grinding it away.

We can have glaciers grinding it away as well.

So as the rock is being uplifted, it's being removed at the top, and

the result is that rock that was once at depth ends up at the surface.

So, in this topic, we've seen how rocks change through Earth history.

We're now going to leave our general description of how rocks form and

how rocks change behind and turn our attention to rocks and you.

In other words, what kinds of useful materials can we get from rocks,

and how do we get them?

[MUSIC]

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