How Old Is The Moon?

Jan 16, 2017 By James H, Young Editor
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How old do you think the moon is? A few million or billion years, right? Surprisingly, we do not know its exact age.

However, scientists have recently discovered two new and interesting things about the moon. Examining moon rocks collected in 1971, one team of researchers has calculated the age of the moon, while another has proposed a new theory on how the moon was formed.

Let’s dive in, and find out what really happened all those years ago.

How Was The Moon Formed?

No one knows exactly, but quite a few theories have been proposed about the moon’s formation. One theory states that the Earth and moon formed at the same time, another that the moon was created from leftover debris after the planets formed. A more realistic theory is that the Earth could have “captured” the moon - in other words, pulled the moon into its orbit.

However, the most widely accepted theory on how the moon was formed is the “giant impact” theory. According to this theory, a meteorite the size of Mars crashed into the Earth a very long time ago, blasting material into space and creating the moon. But things just don’t add up. If the giant impact theory were true, the moon should be mostly made of material from the meteorite. However,  the moon rocks that were collected had very similar chemical composition to rocks on Earth.

Recently, scientists have proposed a slight twist— that it might not have been just one meteorite.  In fact, they think the moon might have been created through many impacts. When an object from space crashed into Earth, debris from the collision formed a disk around our planet; over time, that disk condensed into a “moonlet”. After this process repeated several times (at least 20, according to the researchers’ calculations!), the moonlets merged together and condensed into what we now know as our moon.  

How Old Is The Moon?

Now, onto the moon’s age. Another team of scientists has now predicted the moon to be about 4.51 billion years old (give or take 10 million years). This is much older than previous estimates, so how did they figure that out? They used a material called zircon, a radioactive mineral that is preserved amazingly well within moon rocks.

By studying the zircon inside the moon rocks, the researchers tracked the radioactive materials inside, which decay at a constant rate. After seeing how much decay had occurred, they could “turn back the clock” and calculate how long ago the zircon had formed. According to their conclusions, the rocks and the moon date back to 4.51 billion years ago, 60 million years after the formation of the solar system. So, if this study proves to be right, the moon is a lot older than anybody thought.