Scientists formerly believed that the rocky planets—Earth, Mercury, Venus, and
Mars—were created by the rapid gravitational collapse of a dust cloud, a deflation
giving rise to a dense orb. That view was challenged in the 1960s, when studies of
Moon craters revealed that these craters were caused by the impact of objects that
were in great abundance about 4.5 billion years ago but whose number appeared
to have quickly decreased shortly thereafter. This observation rejuvenated Otto
Schmidt’s 1944 theory of accretion. According to this theory, cosmic dust gradually
lumped into ever-larger conglomerates: particulates, gravel, small and then
larger balls, planetesimals (tiny planets), and, ultimately, planets. As the planetesimals
became larger, their numbers decreased. Consequently, the number of collisions
between planetesimals decreased.
- Which of the following best describes the “observation” (line 6) referred to in the
passage?
A The rocky planets were created by the rapid gravitational collapse of a dust
cloud.
B Certain features on the Moon’s surface are impact craters caused by
collisions with objects such as planetesimals.
C The rocky planets were formed by a slow accretion of cosmic dust into
increasingly larger bodies.
D The number of objects colliding with the Moon appears to have been high
for a while and then rapidly diminished.
E There are far fewer planetesimals in existence today than there were about
4.5 billion years ago.
Why is the answer D and not E?
The passage states “studies of Moon craters revealed that these craters were caused by the impact of objects that were in great abundance about 4.5 billion years ago but whose number appeared to have quickly decreased shortly thereafter.”
Option D talks about the “frequency” of objects colliding with the moon which is not what the passage states. It says the number of such objects reduced greatly but how do we know how often these objects were colliding with the moon even when their number was high?
Option E on the other hand just talks about the number of objects being less now compared to before. That matches better with the information from the passage right?