Hi Wee TAN, Almost the entire Solar System formed 4.6 billion years ago, when the solar nebula collapsed. However, astronomers think that the Moon formed later than that, when a Mars-size protoplanet smashed into the Earth. The fragments from the collision splashed into orbit around the Earth and then reformed into the Moon, which still orbits us today. Astronomers think this collision happened about 4.527 billion years ago, about 30-50 million years after the rest of the Solar System formed. This is the main theory of how the Moon formed, but there are others. It is possible that the Moon was captured by the Earth’s gravity, or it just formed in place around the Earth after the formation of the Solar System. Evidence for this collision was found by the astronauts of the Apollo Moon landing missions. They found lunar rocks that have oxygen isotope compositions which are nearly the same as the Earth. This means that portions of the Moon were once part of the Earth. Actually, both the Earth and the Moon are made of rocky surfaces and iron cores, but the
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