Question

A recent theory attributes the origin of the moon of the impact of a Mars-size body with the Earth. Which of the following is both a true statement and supports the impact theory of the moon’s origin?
A. The scar left by the impact can be identified with the Pacific Ocean.
B. The composition of the moon is similar to Earth’s but somewhat different
C. The moon is older than the Earth
D. The remains of the impacting body now forms the Earth’s core.

Answer 1

Firstly, brush-up all your prior knowledge on the impact theory of the moon’s formation. Go through all the evidence that supports this theory. You may also think of how the basic model of this theory was explained and hence find out which among the given statements is one among the proofs of this theory.

Complete answer:
We have so many theories that explain as to how our natural satellite moon was formed. The most widely accepted among all those theories is the giant-impact theory. Before directly discussing the giant-impact theory, let us go into a brief discussion about all the other theories that explains moon formation.
We have capture theory that suggests that the moon was once a wandering body, almost like an asteroid, formed somewhere within our solar system and was captured by Earth’s gravity while passing nearby.
Another contrasting theory is the accretion theory that suggested that the moon and earth was formed together, that is, the moon was once a part of earth itself. Then fission happened for earth which had been spinning with very high speed. Thus, some material broke away and began to orbit the planet.
Theia impact, the big splash, the giant-impact hypothesis- are all the names of that theory which says the moon formed as the resultant of a collision between the proto-Earth and a Mars-sized colliding body called theia. Some of the evidences include:

1. Samples that we have of the moon that indicates once molten nature of the moon’s surface.
2. Lower density and relatively small iron core of the moon.
3. Their similarity in orientations.
4. We also have stable-isotope ratios of lunar and rocks on earth that clearly implies a common origin.
   So the basic model of this theory goes like this: Theia might have hit the Earth when it was about to complete its formation. It is believed that Theia’s iron core would have sunk into the young Earth’s core along with its mantle also being accreted into Earth’s mantle. Significant portion of both their mantle might have undergone fission and then resulted in the moon formation.
   Among all the given statements, ‘The remains of the impacting body now form the Earth’s core’ is the true statement and also supports the impact theory.

Hence, the answer to the given question is option D.

Note:
We all know that the very basis of scientific events is theories. Even the same scientific event (cosmological events) may have numerous theories put forward by various scientists giving different explanations each better than the other. As a scientist, we should consider each assumption valuable.