L2
讲座
1. What is the lecture mainly about?
The role of the dryas flower in identifying ice ages
The relationship between the Younger Dryas and a global-warming trend
The reasons why the Younger Dryas occurred
The reasons why the Younger Dryas was so short
2. According to the professor, what is unusual about the Younger Dryas?
It occurred only in areas where the dryas flower lived.
It consisted of several mini ice ages.
The climate change occurred over a relatively short period of time.
The temperature decrease was small compared to that of most other ice ages.
3. What does the professor say could affect global ocean currents?
Increased evaporation over the ocean
A change in the amount of fresh water flowing into the ocean
Change in the movement of Earth’s crust
An increase of sediment at the bottom of the ocean
4. What do the ice-dam theory and the meteor-impact theory both assume?
That all vegetation died during the Younger Dryas
That melting ice caused the Younger Dryas
That the Younger Dryas contributed to modern-day warming
That the element iridium played a key role in the Younger Dryas
5. Why does the professor mention a cloud of dust?（多选题）
To explain how the North Atlantic conveyor belt works
To provide evidence for a decrease in temperature at the beginning of the Younger Dryas
To emphasize the speed at which climate change can occur
To explain how iridium deposits worldwide relate to one theory about the Younger Dryas
6. Why does the professor say this:
To point out an apparent inconsistency with one of the proposed theories
To ask the students to think of an answer that is not presented in the textbook
To suggest an alternate theory about the cause of the Younger Dryas
To emphasize a point he made in a previous lecture
