Why Does Planet Earth Have So Much Water?

by Max Moreno, age 14

For nearly all of Earth's existence, water has played a crucial role in life. However, scientists continue to study how it got here.

When Earth was still forming, it was too close to the Sun and therefore too hot for any water to exist. Many theories try to explain how Earth got its water, but none of these theories have been proven. Most modern theories suggest that water came from outer space during Earth's first 100 million years.

One common theory is that, while the solar system was still forming, many asteroids and other objects collided with Earth. Those objects could have contained ice, which then melted and turned into water. Over millions of years, this may have been the reason why Earth is now covered with water.

Some scientists believe water could have formed on Earth itself, not from objects in space. Scientists at UCLA and the Department of Earth, Planetary, and Space Sciences believe water on Earth was created from hydrogen. When magma heats hydrogen, it reacts with iron oxide in the magma, creating water. Water could also have come from both sources, as evidence supports both.

There is no way to know for sure which theory is correct, but as scientific research advances, we will one day get a clearer picture of how water got to Earth.

[Sources: Paris Observatory; DongA Science; Carnegie Science]