Dating the Moon: What’s 60 million years between friends?

Image taken from Moon orbit by the Apollo 8 astronauts. [Credit: NASA]
Image taken from Moon orbit by the Apollo 8 astronauts. [Credit: NASA]
The early Solar System was a violent place. The planets and other large bodies formed when small rocks smashed into each other and gradually gathered up enough mass to form spheres under gravity. Even then, their surfaces were bombarded by meteorites, only gradually cooling. The Moon likely formed when a Mars-sized protoplanet crashed into the molten Earth, breaking off a large chunk.

For that reason, we can’t pinpoint the exact date Earth formed: the Moonsplat effectively erased the record of anything that came before it. From meteorite studies, we know how old the Solar System is, and we know how old the most ancient rocks on Earth are, but Earth’s age falls in between those two. Now authors of a new study have proposed a refinement to the date of the Moon-making impact, which would push back the formation by about 60 million years (give or take 20 million).

As I explained in my most recent column for The Daily Beast, this revision helps us get closer to a picture of the early Solar System:

If it’s such a slight difference compared with the 4.5 billion years of Earth’s history, those 60 million years might not seem that important. However, a lot can happen in that amount of time—and an older Earth compresses the amount of time for it to form and cool down, making our planet’s earliest years an even more interesting time. [Read more…]

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