How Did the Moon Form?

By: Earth How · Last Updated: May 17, 2020

The giant impact hypothesis models the formation of our moon. It describes the moon’s collision course with Earth.

The giant impact theory is identical to the “Theia impact” in which Earth is called “Gaia” and the moon is “Theia”.

Scientists estimate the formation of the moon to be around 4.5 billion years ago.

The Earth is constantly being bombarded by small asteroids and comets. But rare events are larger like the one that formed our moon.

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Earth Meet Moon

Here are the steps that outline the “Giant Impact Hypothesis”:

COLLISION COURSE: The “Giant Impact Hypothesis” starts with an object the size of Mars heading towards Earth. At tremendous speed, this object collides into Earth.
INDIRECT COLLISION: It wasn’t a direct collision of the two protoplanets but more of a glancing blow. Earth’s planetesimal rock are ejected out into space.
GRAVITATIONAL PULL: But the force of gravity prevents all the debris from flying too far away in space. Eventually, the leftover debris coalesce in orbit to form the moon.

Ever since the giant impact, the moon has remained orbiting the Earth. And because of the giant impact, it tilted Earth on its axis promptly giving it seasons.

Why does the moon and Earth have similar compositions?

The composition of the moon and Earth are very similar. One big difference is that the moon does not have as much iron.

Scientists think that from the giant impact collision, the iron core of the moon got absorbed by the Earth. Also, less of the heavier elements like iron got thrown out into space.

As the lighter elements from Earth were flung out into space, the moon absorbed them. Eventually, the moon became a dead cinder of rock orbiting the Earth.

So not only does the Earth has more iron than moon, but it has a higher density. And measurements can confirm these conditions to be true about the moon.