听力音频：
L1：
1. What is the main purpose of the lecture?
To illustrate similarities between two periods of climate change
To examine theories about the extinction of large North American mammals
To describe how scientists verify occurrences of meteor impacts on Eart
To present a new explanation for the cause of the end of the last ice age
2. What is the professor’s opinion of the claim that cooling during the Younger Dryas caused a major extinction?
It will probably be proven correct by future research
It has been strongly contradicted by recent soil-sample analysis
It seems unlikely in view of what is known about similar climate changes
It is based on a misinterpretation of evidence collected in North Americans
3. Why does the professor mention a meteor that struck Earth during the time of the dinosaurs?
To imply that that meteor impact also affect other large animals in North America
To point out that Earth was often struck by meteors in the past
To explain why it is to hypothesize that a similar impact could have caused a later extinction event
To challenge a commonly accepted claim about dinosaur extinction
4. According to the professor, what is the major significance of the Younger Dryas Boundary?
It provides proof of a sudden climate change.
It lines the inside of a 13,000-year-old impact carter.
It contains valuable information on about the composition of meteors.
It marks the disappearance of large mammal species.
5. The professor mentions that a new group of researchers collected samples from a Younger Dryas Boundary site. How did those researchers explain the high concentration of magnetic particles in the samples?
The Younger Dryas Boundary is especially thick at that site.
The particles were carried to the site by flowing water.
A meteor caused a high concentration of the particles at the site.
Old roofing material had been buried at the site.
6. What opinion does the professor express when he discusses nanodiamonds?
Their presence is not strong proof of a meteor impact
They indicate that a geological sample has been contaminated
Researchers should get a better understanding of their origin
Researchers should focus on magnetic particles instead of nanodiamonds
