Before 4.5 billion years ago, Earth had a rocky beginning. We had just collided with an early planet the size of Mars, a cataclysmic event that melted both planets and created our moon from a large lump of lava. This effect set the stage for the Hadean Eon, which got its name from the Greek god of the underworld, Hades.
It was a name for Earth’s mostly hellish climate at the time, when it was so hot that gaseous rock could be found in its atmosphere. Temperatures around 2,000 degrees Celsius are being discussed. As the Earth and moon began to cool, however, liquid water began to form on the Earth’s surface. Considering that around 366 quadrillion gallons of water cover approximately 71% of the Earth, this seems normal. Except for the fact that we shouldn’t have that water because we developed too close to the sun. Mercury, Venus, and Mars are all extremely dehydrated.
where did our water come from and why do we have so much?
Even though the question is complicated and still up for debate, it is thought that our water came from meteorites, space dust, and even the sun. Water is actually not that uncommon in our solar system; it’s just more distant.
Jupiter’s moon Europa, for instance, is a quarter the size of Earth yet possesses twice as much water as we do. This is due to the fact that Europa developed at a greater distance from the sun. So, at the dawn of our solar system, we were all made of stardust. Our solar system is made up of a nebula, which is the dusty remains of a dead star.
As the stardust clashed and imploded, our sun was formed. And the gravity of this nascent sun caused the remaining material to whirl around it in a cloud known as a protoplanetary disk. Yet our early sun was extremely intense, and the dust disk soon began to distinguish. Light gases were blown away from the sun by solar and magnetic winds, leaving behind mostly heavy things like iron and silica. So, Earth is a rocky planet because there was a lot of iron and silica in our part of the protoplanetary disk. We had some of the components for water, but not all of them.
Water is made up of hydrogen and oxygen, and since oxygen is pretty dense, we have a lot of it. Even though oxygen only makes up about 21% of our atmosphere, it binds to silica and iron so easily that it is the most common element on Earth, even though it only makes up about 21% of our atmosphere. However oxygen is only a portion of what is required for water, and hydrogen is so light that it was blown towards Jupiter, Saturn, and other planets, which now have a great deal of water ice.
Where did the missing element come from? When did hydrogen arrive, and where did it come from?
The simple answer is that it was thrown at us. Water ice and hydrogen reside in the outer solar system, but occasionally they enter the inner solar system as asteroids and meteorites. And there is a form of meteorite known as a Chondrite that contains water. But I don’t mean full of water like a Gusher; you can’t crack open a meteorite like a coconut and drink star water from it, as much as I and we would like to.
Instead, the lone hydrogen atoms and full H2O water molecules have formed part of the chemical structure of the chondrite rocks. These minerals include serpentine, chlorite, and smectite, which retain their water tenaciously. This is how the majority of Earth’s water is currently held; while we have a lot of liquid water, we estimate that Earth’s rocks contain around 18 times as much water as our seas do!
How then is water extracted from these minerals?
The simplest method is to melt it which is not guaranteed by just hurling these water-bearing minerals towards the Earth. Indeed, solid chondrite meteorites have struck our planet and not melted. But, this is because they arrived today.
If they had struck Earth in the Hadean, the story would have been very different. During the start of the Hadean, anything that landed on the surface would have melted into our magma oceans. There, hydrogen reacted with oxygen, and the resulting superheated water turned into gas. Since water vapor is lighter than magma. It would rise and escape into the atmosphere.
But, this process was a race against time, as the surface of our magma was cooling, and once a solid rock cap developed, no more water could escape. The oldest evidence of rocks discovered are approximately 4,4 billion years old. Therefore this is likely when the solid rock cap originated. Yet, these rocks reveal an unexpected fact: they were exposed to a liquid ocean.
As soon as the Earth cooled sufficiently to lid the magma, an ocean appeared. It likely differed slightly from the oceans we see today. In the early Hadean, Earth’s atmosphere was heavy with carbon dioxide and maybe as thick as 215 bars of pressure, which is 215 times what it is presently. With so much pressure and heat, the Earth’s surface seemed strange.
Water is currently transforming into a gas at temperatures around 100 degrees Celsius. But if you alter the pressure, you can alter the point at which water turns into gas. At the summit of Mount Everest, where the air pressure is a third of what it is at sea level, water converts to gas at a temperature of only 68 degrees Celsius.
And in the Hadean, where the atmosphere was somewhat denser, the opposite was occurring. Even when the surface temperature reached 230 degrees Celsius, the water did not boil. Hence, the initial ocean was hyper-heated. The superheated ocean did not stay long. By the conclusion of the Hadean period, 4 billion years ago, the earth’s surface was quite similar to what it is now, with a rocky crust, an ocean of liquid, but not superheated, water, and an atmosphere of roughly the same pressure as it is today.
The story of water on Earth should go from meteorites to lava to air to superheated oceans. But, there is one major flaw in this scenario. It turns out that the water and hydrogen in chondrite meteorites don’t have the same chemical makeup as most of the water on Earth, which is the water in our rocks.
When we refer to chemical composition, we are referring to isotopes or hydrogen types. There are two extremely essential isotopes of hydrogen: ordinary hydrogen, which has one proton and one electron, and Deuterium, which has one proton and one neutron.
Due to the inclusion of a neutron, Deuterium is “heavier” than hydrogen. The majority of deuterium in our solar system was produced during the Big Bang. And it is a significant constituent in chondrite meteorites. They are “laden” with an ancient form of hydrogen. The oceans are also quite dense, but our modern oceans are not a good reflection of our primordial water.
First, they are not 230 degrees Celsius, and second, they’ve been resting on Earth’s surface for 4.4 billion years, so we know they’ve changed. Weirdly, we have to look at the water stored in our rocks to figure out what our liquid water looked like 4.4 billion years ago. When the Earth’s magma seas cooled enough to form a hard rock seal, not all of the water in the magma evaporated into the air.
The majority of it was trapped in the Earth’s Mantle, a layer under the surface. By plate tectonics, parts of the mantle have been pushed to the surface over time, allowing us to examine the hydrogen content of mantle rocks. It is also much lighter than the hydrogen found in the oceans. Which is part of the reason why the origin of Earth’s water is still somewhat debatable.
How could we have such light water in our rocks if chondrites have such heavy water?
In the past ten years, this issue has been the subject of extensive study. There is a type of meteorite known as an enstatite that contains lighter hydrogen, but the majority of scientists believe there are not enough of these meteorites to make up the difference. Then, in 2021, scientists reported that they had found some interesting samples on an asteroid and may have found the answer.
They discovered that the samples contained an exceptionally high amount of light hydrogen. To confirm their growing worries about where the hydrogen came from, however, they had to repeat the process. So, they measured the amount of hydrogen and water in olivine crystals before and after they were exposed to something like solar wind. After looking at them, they found that, like the asteroid samples, they had a thin layer of light hydrogen-water crust on top.
So when did this clear water originate?
The water is truly light because it sprang from the sun. Our sun’s solar winds release several particles, including protons. When protons collide with dust, they can sometimes steal one electron. And light hydrogen is formed when a proton and an electron combine. This light hydrogen combined with a rock containing oxygen produces light water. Or, more realistically, smash the hydrogen ion into a meteorite or some localized space dust. When this material falls to Earth, it transports light water into our magma ocean, which is eventually locked in the mantle. So, the history of water on Earth is complex.
