Day 1

Professor

: In our last class, we talked about the formation of Earth and the other rocky planets, you know, planets in the inner solar system. So what about the gas giants; Jupiter...Saturn...Uranus... Neptune? Well, we have two different theories. But first, let’s back up. Scientists believe that our solar system began as a huge spinning cloud of dust and gas, which eventually grew hotter and denser in the center. The center of the cloud contracted into a ball of hot gas and dust, eventually becoming our Sun. And... can anyone tell me what happened to the remaining cloud... to the disk encircling the Sun when it was a young star?

S: The inner rocky planets were formed. Um... Dust, metal, and asteroids of all different sizes within the disk collided with each other and clumped together. And this process kind of snowballed over millions of years until the trunks grew into many planets... of protoplanets.

P: Right! This process is what’s called ‘accretion’. And we call the disk an accretion disk. Now you can see it as two parts, an inner accretion disk and then outer accretion disk. In the inner part, once an object gets larger enough, that object’s gravitational field becomes stronger which increases the speed of the accretion process... you know, smaller ones are attracted and sort of get gobbled up by larger ones. And eventually you get a fully-grown planet in its own orbit. OK. That’s how the inner rocky planets are probably born by accretion.
But what about those gas planets in the outer solar system in the outer accretion disk? Well, the first theory holds that the accretion process was pretty much the same as the one that formed the rocky planets with some key differences.

1. What is the lecture mainly about?

(A) Two new theories about the formation of rocky planets
(B) Competing theories about the formation of gas planets
(C) Formation of Jupiter, Saturn, Uranus, and Neptune
(D) How the birth of young stars affects the formation of gas planets

[문제유형] Main Idea Q

― 이 유형은 첫 번째 문제로 등장한다.
― 전형적인 오답으로는 다음과 같다.
― too specific / too broad / not mentioned(keyword는 있으나, 해석을 보면 언급하지 않은 경우이니 조심해야 한다)

[해설]

― 과거시제나 현재완료시제는 지난 시간의 topic 을 알리는 signal 임을 기억한다.
― today’s topic 의 signal 은 다양하지만, 위의 지문에서 signal 은 이었으니, 이 signal도 외워둔다.
― 다음의 keywords 는 이다.

[정답] B