OFFICIAL50 Why does the professor say this:

[00:00.40]NARRATOR: Listen to part of a lecture in a geology class.[00:04.94]MALE PROFESSOR: All right, class. Let's get started. [00:06.82]Um, last time we finished up our section on coal, so we have just two fossil fuels left to talk about, [00:13.55] and those are petroleum and natural gas. [00:16.61] Today I'll concentrate on petroleum; and we'll get into natural gas tomorrow.[00:21.29]Like coal and natural gas, petroleum has been formed over millions of years from the remains of prehistoric plants and animals.
[00:30.32]And, like coal and natural gas, it's found in the rocks of Earth's crust.[00:35.26]In fact, the word “petroleum” literally means “rock oil.” [00:39.53] 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.”
[00:50.30]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. [01:04.01] 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. [01:12.26]Anne?[01:13.99]FEMALE STUDENT: But what kind of organic materials, I mean, specifically what kind of dead plants and animals make up petroleum, exactly? [01:22.25]Do you mean, like trees and dinosaurs?[01:25.30]MALE PROFESSOR: Well, apparently petroleum's usually made from simple, one-celled marine animals and plants… algae, for example. [01:33.07] What happens is, this accumulated plant and animal material that originally came from the ocean gets covered by sediment [01:40.39]and then is, um, eventually exposed to Earth's internal heat and pressure for millions of years. [01:47.45] And over those millions of years, the heat cooks and the pressure molds that material, turning it into a thick, sticky liquid. [01:56.47] 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? [02:06.17]Yes, Anne?[02:07.56]FEMALE STUDENT: I've heard people talk of, um … “live” and “dead” oils.[02:12.34]MALE PROFESSOR: Well, um, when crude oil has a lot of natural gas mixed up with it, it's called live oil. [02:19.51] But if the gas escapes from the mixture, then the oil is said to be dead [02:23.78]and it's heavy and more difficult to pump. [02:27.13] Does anyone know how the gas separates, ah, from the oil? [02:31.51]Sam, go ahead.[02:32.76]MALE STUDENT: Doesn't it happen when the oil shoots up to the surface?
[02:36.36]MALE PROFESSOR: Yes. That’s right. [02:37.40] When oil reaches the surface of the earth, there's less pressure on it, [02:41.45] and with less pressure, the oil and gas are able to separate. [02:45.24]The other way that crude oil is able to come to the surface is by people pumping it up out of the ground. [02:50.66] And, ah, it’s the same thing that happens: at the surface, there’s less pressure, and so the oil and gas separate.[02:57.98]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…[03:09.98]that's really rare. [03:11.45] The majority of the petroleum is just filling in the tiny pores and cracks in rocks.[03:18.55]Now, um, a little more on the petroleum industry. [03:22.44]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. [03:36.24] Then it pumps the crude oil out. . [03:38.77]Then its refineries have two main tasks: convert less–valuable crude oil into a more valuable form, and create usable products from refined oil.[03:50.00]Basically, the refineries do this by boiling the oil.
[03:53.11]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. [04:08.22] 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! [04:16.56] So you can see, petroleum is essential to today's industrial society.[04:22.27]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. [04:33.36]And I'd like you to read over the packet of information I'm about to hand out to you before we go. [04:38.88]It should familiarize you with the history of the oil field we'll be touring as well as the details of their project.