Why we think Theia existed

The giant-impact theory suggests that billions of years ago, an object roughly the size of Mars, called Theia, crashed into the young Earth.

This massive burst of energy dramatically changed Earth's rotation and sent fragments flying out into space. These particles eventually came together to create the Moon over an extended period.

It remains uncertain whether Theia actually existed and collided with the early proto-Earth, yet the supporting evidence is quite strong.

Firstly, we are the sole rocky planet possessing a significant moon. Neither Mercury nor Venus has one, and Mars can only lay claim to two tiny, captured asteroids. The presence of such a large moon necessitates an explanation.

Secondly, consider spin. Our planet rotates significantly quicker compared to the other terrestrial worlds, and the Moon circles around us at an unexpectedly rapid speed. This suggests that something profound in our distant history imparted this considerable amount of energy, which can be simply accounted for by a collision with another forming planetary body.

Finally, we encountered an unforeseen piece of evidence during our lunar expeditions with humans. The Apollo missions weren’t just quests for prestige; they were genuine scientific endeavors. Equipped by skilled geologists, the Apollo astronauts, starting with Armstrong and Aldrin, learned how to seek out and collect significant discoveries.

When they came back from Earth, what was uncovered showcased an immense trove of scientific information about the Moon’s makeup. This was due to our unprecedented ability to gather significant quantities of regolith— the broad term for the unconsolidated particles forming the Moon’s exterior—for analysis here on Earth. In total, all six successful Apollo missions collected around 2,200 specimens weighing nearly 400 kilograms altogether.

The regolith brought back by the Apollo missions revealed an intriguing characteristic: the composition of the lunar surface strikingly resembles that of the Earth's crust, featuring comparable proportions of various elements. This leads us to conclude that both must share a common source.

Even though we cannot rewind time to observe the birth of the Earth and Moon directly, we can piece together their origins using the evidence dispersed throughout our surroundings to unravel this monumental occurrence from more than four billion years past.

Provided by Universe Today

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