Where does Earth's water come from? Scientists find liquid water in meteorites, water is ubiquitous in the solar system

Seventy percent of the earth's area is ocean, so the earth is called the blue planet. However, how did so much water on the earth come from?

There are two theories about the origin of water on Earth. One argument is that the water on the earth is self-contained. As the planet cooled, water vapor on the planet condensed, accumulating on the ground and forming oceans. Another theory is that asteroids kept hitting the earth, bringing a lot of water to the earth.

First, it is true that asteroids brought water to Earth. The solar system formed from a nebula 4.5 billion years ago. Large planets like Earth gradually absorb the matter in space and grow up little by little. From 4.5 billion years to 3.8 billion years, those small stars that failed to grow into large planets, as well as a huge number of asteroids, collided with those large planets under the action of gravity. It is generally believed that about 4.5 billion years ago, Earth and a Mars-sized body collided to form the moon.

At the end of this phase, the period from 4.1 billion to 3.8 billion years, the impact became more and more violent, known as the Late Heavy Bombardment (LHB). During this period, a large number of asteroids and comets crashed into the earth and the moon, and many craters on the moon were formed at this time. At the same time, the arrival of asteroids and comets also brought a lot of water to the earth. Therefore, a considerable part of the water on Earth, perhaps formed in the early years on the edge of the distant solar system, came to us with the fall of the comet.

Early Earth and Oceans

If Earth's water comes primarily from asteroid impacts, then Earth's oceans wouldn't have formed too early. Scientists had previously thought that Earth's surface was molten for the first few hundred million years, and then gradually cooled, allowing oceans to form. There is clear evidence that Earth's oceans arose at least 3.8 billion years ago. Ancient rocks found in Quebec, Canada, show that water existed on Earth 4.28 billion years ago. Even more interesting, zircon ore found in Western Australia shows that the Earth had water 4.4 billion years ago. This means that the surface temperature of the earth dropped very quickly after it was formed, otherwise the water could not be retained. From this perspective, perhaps water was part of the Earth when it formed from it.

A recent article in Science Advances further revealed that water was likely part of the formation of the solar system's large planets. The authors of the paper studied a Martian meteorite, NWA 7533, that fell in northwestern Africa.

Discovered by a Bedouin tribe in the Sahara Desert, this meteorite is a very old rock, 4.43 billion years old. The oldest solar system material that humans have found on Earth so far is contained in the meteorite NWA 2364, which was discovered in Morocco in 2004 and is 4.5682 billion years old, older than the age of the Earth. This is roughly when the solar system began to form. Anyway, the NWA 7533 qualification is definitely very old. It is generally believed that it formed only 90 million years later than Mars. Later, it was knocked out of Mars in an asteroid impact on Mars, and after a long journey, it came to Earth again.

Scientists found strong signs of oxidation on the meteorite, which should have occurred when the asteroid hit Mars. Such oxidation is only possible when there is water on the surface of Mars. In other words, Mars had water on its surface 4.43 billion years ago. It is generally believed that early Mars had a large amount of liquid water and a large ocean. It now appears that water on Mars not only appeared after Mars formed. In terms of time, 4.43 billion years was before the massive water-rich asteroid hit Mars. Therefore, the water at that time can only be brought by Mars when it was formed, not by asteroids.

Combined with the situation on Earth, this shows that the rocky planets of the solar system already contained water when they were formed. Venus, for example, also had oceans in the early days, and then the surface water was slowly lost due to the greenhouse effect. Some studies suggest that Venus had water on its surface until 700 million to 750 million years ago. Even Mercury, which is very close to the sun, with a maximum surface temperature of 400°C and no atmosphere, was found to have ice on its surface. There are a total of four large rocky planets in the inner solar system, all of which have been found to have water on them.

In this way, we can have a preliminary conclusion as to how the water on earth came from. The Earth cooled down shortly after its formation, and the hydrogen in the Earth's interior quickly combined with oxygen to form water. This is the original source, or even the main source, of water on Earth. Later impacts of asteroids and comets on the earth brought more water to the earth.