Narrator Listen to part of a lecture in an archaeology class. Now get ready to answer questions. You may use your notes to help

Narrator
Listen to part of a lecture in an archaeology class.
Professor
Last time we talked about the discovery of dinosaurs and today we are gonna have a discussion on the study and preservation of fossils. People sometimes ask, "Why waste time studying fossils?" Studying fossils is far from being a waste of time, because... uh... we can learn many useful facts from them. Generally speaking, fossils are especially important...um...because they are the only clues to the existence and appearance of life on Earth millions of years ago. Now, you may have a question, " how do fossils tell the existence and appearance of life on Earth?" You see...um...fossils are arranged in proper geological order. So, they reveal how life has steadily developed from the primeval creatures to the...the complex animals of today. Such knowledge helps us to understand the origins and evolution of life. What I mean is that such knowledge helps us to understand a little of what we ourselves are.
    In addition, fossils can also be used to identify different kinds of sedimentary rocks...like...the rocks below ground level or those separated by miles of ocean. Even rocks which are at very great depths can be identified by their fossil contents. What I’m trying to say is...um...that fossils are valuable aids to mining and petroleum engineers. What it means is that fossils can help mining and petroleum engineers to find oilfields. Of the fossils, the microfossils are particularly helpful. The microfossils refer to the tiny fossils. How are they used to find the oilfields? First, the engineers separate...um... the tiny fossils from the rocks they have got by drilling. And then, the specimens are examined under a microscope. According to the info obtained from these specimens, the engineers can tell whether the rocks are of the kinds associated with oilfields. In other words, these tiny fossils can tell whether the place has oils or not.
    Alright. Now, I would like to talk about the preservation of fossils, that is, how fossils are preserved. Different fossils have been preserved in different ways—some are preserved as moulds or casts. What I’m trying to say is that some have been preserved in a shape of a plant or animal left in rock. Others are preserved as frozen dead bodies. The most remarkable fossil remains are some Polish rhinoceros remains. These remains...um...were completely filled with oil. So...uh...they were finely preserved. One actually can see the animal’s flesh, skin and hair. Isn’t this amazing? So, another very rare way in which animals can become fossilized is through dehydration, that is, through drying up something by taking off all the liquid. Speaking of dehydration, you may think of mummies in Egypt. The process of making mummies is called dehydration. In terms of fossilization happens in arid conditions, which means it happens in dry places with no moisture at all like the desert. Or...um...it happens in a continually dry atmosphere. This dry atmosphere makes happen the complete...um...dehydration of all soft parts...before the body decays. For example, in New Mexico and Arizona, mummies of sloths have been found in caves and volcanic craters. The skin, hair, and claws of the sloths can be clearly seen.
    Finally, some insects were fossilized by being trapped in amber. These fossils show great details of the insects and have been found in countries...bordering the Baltic Sea. The fossils of these insects represent another and a very interesting way in which life forms have become fossilized.
Now get ready to answer questions. You may use your notes to help you answer.
18. What does the professor mainly discuss in the lecture?
19. Which of the following does the professor mention as the benefits of the study of fossils?
20. What are the ways of preserving fossils mentioned in the discussion?
Listen again to part of the lecture. Then answer the question.
Professor
Generally speaking, fossils are especially important...um...because they are the only clues to the existence and appearance of life on Earth millions of years ago.... Now, you may have a question, "how do fossils tell the existence and appearance of life on Earth?"
21. What does the professor imply when he says this?
Professor
Now, you may have a question, "how do fossils tell the existence and appearance of life on Earth?"
22.Why does the professor say this?
Professor
What I’m trying to say is that some have been preserved in a shape of a plant or animal left in rock.
23. How does the professor introduce fossilization through dehydration?