Narrator: Listen to part of a lecture in an astronomy class. Professor: Now, one of the most surprising discoveries about Mars is evidence of ancient riverbeds. But how could liquid water exist on a planet that is now so cold and dry? The answer lies in Mars's early atmosphere. Billions of years ago, Mars likely had a thicker atmosphere, rich in carbon dioxide, which created a greenhouse effect. This trapped heat and allowed water to flow on the surface. However, over time, solar wind stripped away much of this atmosphere because Mars lacks a global magnetic field. Without that protection, the planet lost its ability to retain heat, and surface water either froze or evaporated into space. Some water may still exist as ice at the poles and underground. In fact, recent data from orbiters suggest that salty water might flow briefly on Martian slopes during warmer seasons. This raises an exciting possibility: if liquid water exists today, could microbial life survive there? Understanding this history is crucial for future missions.
❓ 문제 According to the professor, what is the main reason Mars lost most of its atmosphere?
A. A. The planet's surface became too cold for any atmospheric gases.
B. B. Solar wind stripped it away because Mars lacks a global magnetic field.
C. C. The greenhouse effect became too strong and burned off the atmosphere.
D. D. Liquid water absorbed the carbon dioxide and removed it from the air.
✅ 정답
B. Solar wind stripped it away because Mars lacks a global magnetic field.
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word
