NASA/JPL-Caltech
Hard Science

Move over Asteroids, Earth’s Water May Have Come from…Dust?

Our Pale Blue Dot

New research indicates that Earth’s water may have come from, of all things, dust.

Liquid water covers a vast majority of our planet. In fact, some 70 percent of Earth’s surface is covered in water. And of course, we aren’t talking about little streams, but vast blue oceans that are as deep as our mountains are tall. Water is also a fundamental part of the human body. It seems hard to believe, but we are a staggering 60 percent water—blood is 92 percent water, while the human brain and muscles are about 75 percent water.

Yes, your brain in 75% water.

Scientists have long debated how this water got here. One of the leading ideas is that comets and asteroids brought water to our planet shortly after it formed; however, a new paper published in Nature Geoscience suggests that a sizable portion of our water may have come from water-soaked dust particles that were, at one point, trapped deep inside our planet during its formation.

Breaking Down the Science

Many billions of years ago, Earth was smashed by a massive object known as Theia. This impact event is ultimately what led to the creation of the Moon. The scientists assert that, after the collision, our planet may have consumed all of the water that was flung out into space.

Rock samples that we have taken from the Moon show notable similarities to those that we find on Earth; however, there is one main difference: The rocks have no water. In fact, the rocks are severely lacking in volatile material, such as water, zinc, sodium and potassium.

Based on their calculations, the team asserts that these materials would have been close to the Earth shortly after the collision. This is important because, ever since its formation, our Moon has been steadily moving away from Earth. Currently, it moves away 4 centimeters (1.5 inches) each year. Yet, in the first few decades of the Moon’s life, it would have moved much faster, and as it orbited out, the team asserts that it would have quickly lost the ability to accumulate water and other lighter materials left from the collision.

Instead, as the dust and gas that surrounded the planet interacted with the gravity of the Moon, those materials would have been flung back toward the planet, as opposed to falling onto the Moon.

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