NARRATOR：

Listen to part of a lecture in a geology class.

MALE PROFESSOR：

All right, class. Let's get started.

Um, last time we finished up our section on coal, so we have just two fossil fuels left to talk about, and those are petroleum and natural gas.

Today I'll concentrate on petroleum; and we'll get into natural gas tomorrow.

Like coal and natural gas, petroleum has been formed over millions of years from the remains of prehistoric plants and animals.

And, like coal and natural gas, it's found in the rocks of Earth's crust.

In fact, the word "petroleum" literally means "rock oil."

And, in its original state, the way we find it in Earth\'s crust, it\'s called "crude oil." Sometimes people shorten that up and, ah, just refer to it as "crude."

Um, petroleum also contains natural gas, so usually the petroleum industry is naturally searching for and utilizing deposits of both crude oil and natural gas at the same time.

In other words, companies might as well gather, use, and sell both the oil and the gas when they find it, since both are valuable.

Anne?

FEMALE STUDENT：

But what kind of organic materials, I mean, specifically what kind of dead plants and animals make up petroleum, exactly?

Do you mean, like trees and dinosaurs?

MALE PROFESSOR：

Well, apparently petroleum's usually made from simple, one-celled marine animals and plants... algae, for example. What happens is, this accumulated plant and animal material that originally came from the ocean gets covered by sediment and then is, um, eventually exposed to Earth's internal heat and pressure for millions of years.

And over those millions of years, the heat cooks and the pressure molds that material, turning it into a thick, sticky liquid.

And since petroleum's made from these ocean organisms, you can guess where it's found. It makes sense that we usually find it under the ocean or near shore, right?

Yes, Anne?

FEMALE STUDENT：

I've heard people talk of, um ... "live" and "dead" oils.

MALE PROFESSOR：

Well, um, when crude oil has a lot of natural gas mixed up with it, it's called live oil.

But if the gas escapes from the mixture, then the oil is said to be dead and it's heavy and more difficult to pump.

Does anyone know how the gas separates, ah, from the oil? Sam, go ahead.

MALE STUDENT：

Doesn't it happen when the oil shoots up to the surface?

MALE PROFESSOR：

Yes. That's right. When oil reaches the surface of the earth, there's less pressure on it, and with less pressure, the oil and gas are able to separate.

The other way that crude oil is able to come to the surface is by people pumping it up out of the ground.

And, ah, it's the same thing that happens: at the surface, there's less pressure, and so the oil and gas separate.

But when we talk about how it actually exists inside Earth's crust, most people think that there are huge pools of oil sitting around in caverns somewhere under there... that's really rare. The majority of the petroleum is just filling in the tiny pores and cracks in rocks.

Now, um, a little more on the petroleum industry.

As far as the extraction process, the petroleum industry digs deep wells to reach underground oil fields, where crude oil has accumulated over a large area and is trapped between layers of rocks.

Then it pumps the crude oil out.

Then its refineries have two main tasks: convert less-valuable crude oil into a more valuable form, and create usable products from refined oil.

Basically, the refineries do this by boiling the oil.

When the oil cools off, the stuff that's left is turned into a variety of products, like, ah, gasoline and diesel fuel for cars and trucks, asphalt for roads, um... paints,plastics, even soaps.

And check what you're wearing，If you're wearing something with synthetic fibers what that really means is that it's made of petroleum!

So you can see, petroleum is essential to today's industrial society.

Now, next week we'll be joining graduate students from the Department of Petroleum Engineering to examine the comprehensive field study they're working on in our local oil fields.

And I'd like you to read over the packet of information I'm about to hand out to you before we go.

It should familiarize you with the history of the oil field we'll be touring as well as the details of their project.