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TPO 59- Speaking Question 4

Listen to part of a talk in a biology class.

Professor:

Today I would like to talk about two of the various theories that scientists have advanced to explain the extinction of dinosaurs.

In the first theory, the extinction is associated with a lack of food. In the second theory, it’s an increase in the Earth’s temperature that is considered the reason why dinosaurs died out.

The lack-of-food theory goes like this: An asteroid, a giant space rock, crashed into the Earth, throwing a huge amount of dust into the atmosphere. This dust cloud blocked the Sun’s rays. Now the lack of sunlight was a big problem ‘cause, as you know, plants need sunlight to make their food. But after the asteroid’s impact, no sunlight could reach plants, so many of them died. And this caused animals that ate plants to die. And animals that ate the animals that ate plants… You’re with me?

They all died off. So our dinosaurs, whether they ate plants or meat, became extinct.Now as for the other theory, call it a global-warming theory. Well, some scientists believed that a series of large volcanic eruptions filled the air with carbon monoxide. While the carbon monoxide let the sun’s radiation enter the atmosphere, it did not let it out, which meant that heat was trapped. This caused a significant rise in the Earth’s temperature.

Now it so happens that among reptiles, like our dinosaurs, the gender of the young depends upon the temperature of the eggs. Warmer temperatures make for warmer eggs, and warmer eggs result in more males than females being born.

Supposedly, this is what happened to the dinosaurs. Because of the warm temperatures, fewer females were born, which meant that fewer eggs were being produced, and eventually this led to the dinosaur’s extinction.