Where Did Earth’s Water Come From?

Uncover the mystery of Earth’s water origins, from asteroid theories to the Solar Nebula.

Video of the day January 18th 2020


In the Beginning…

So to truly answer this question, we need to go back to the literal birth of our universe. “But why is that?” you ask, “wasn’t Earth always filled with water?” The answer to that is a bit tricky. Because it depends on what you believe in regards to the creation of the universe. By that, I mean, if you believe in creationism, or the belief that there is a god or gods that created the world and universe, then the answer would be no…but the waters came quickly after the “formation” of the world.

However, for those who believe in the Big Bang, then it’s very logical to understand how the world was NOT born with water, because the explosion of energy that created our solar system and put everything in its place and orbit would not have created water. Or at the very least wouldn’t have created the liquid that we know from now on Earth.

Which of course raises the question of…where did all the water come from? Because it most certainly didn’t just “appear”, and as our planet is basically 2/3’s water, it would’ve needed to be built up a lot over time, even if that “time” was billions of years. Which is accurate to an extent as we know that have been creatures living in the water for billions of years according to scientists, and many even suspect that live was born in water and not on land.

While the search for the “birth of water” may not be what’s taught in history books and in grander discussions of the universe, it doesn’t mean people aren’t trying to find the answer. In fact, some people they have “found” the answer, and it’s via something that is very near and dear to the hearts of many planets…space rocks.

The Rock and Water Invasion

So if it’s true that water wasn’t just born on Earth, then it had to have been created on the planet, or infused on the planet by some outside force. On that account, scientists do agree that over the course of millions and billions of years that meteors, comets, and asteroids hit the Earth, and when they did, they infused the ground with water. Add numerous rocks crashing down over the years and millennia and epochs and all that and you get a large body of water.

I’m sure this somehow seems far-fetched, I would even go so far as to say that some of you didn’t know that asteroids and the like carried water with them. But they do, and we do know that they helped bring some of the water to Earth. How so? Isotopes. Specifically, the isotope of Hydrogen. Even more specifically than that, the version of Hydrogen isotope known as deuterium. The Earth’s water has a certain concentration of deuterium, and that concentration matches the waters that have been found and studied in asteroids and comets.

But wait, there’s a catch, while much of Earth’s waters seem to have been created by asteroids, there are a few inconsistencies, and so many scientists are actually debating whether the asteroid/comet theory is fully accurate.

“It’s a bit of a blind spot in the community. When people measure the [deuterium-to-hydrogen] ratio in ocean water and they see that it is pretty close to what we see in asteroids, it was always easy to believe it all came from asteroids.” said one scientist

But that begs the question, why don’t they believe it all came from the asteroids?

The Shape Of Water

Ok, I couldn’t resist that title, I do apologize in advance. *ahem*

Seriously though, the question of why the asteroid theory doesn’t work is an important one. Mainly because the asteroid theory works as a plausible method for how the water on Earth came to be. With the exception…of one question. How is it that the Earth was hit by SO MANY asteroids, comets, and such to where 2/3’s of it were covered by water?

No, really, think about it, the Earth isn’t just covered in water, it’s covered in water that is tens of thousands of feet deep. One of the deepest points in the ocean is the Mariana Trench at over 36,000 feet in depth, and it really does keep going on from there. So add that depth, to 7 oceans, innumerous lakes, rivers, and more, and you get…a whole lot of water.

So how is it possible that there were enough meteors, asteroids, comets, and more hitting the Earth in the beginning part of the universe that it would cause that much water to be made? It doesn’t add up for a lot of scientists.

Now again, there’s no denying that some asteroid water was brought to Earth, the isotopes prove that. But what some scientists apparently choose to ignore is that the levels aren’t always so balanced, and they don’t make up for the inconsistencies noticed in that isotope across the world. Meaning that while asteroid water is PART of what made our watery planet, it’s not the only thing. And that is a very important distinction.

So what did create the rest of Earth’s water if not the asteroids and comets?

Scientists estimate solar nebula's lifetime | MIT News | Massachusetts  Institute of Technology

The Solar Nebula

“The solar nebula has been given the least attention among existing theories, although it was the predominant reservoir of hydrogen in our early solar system.”

The other main theory behind where much of the water on Earth came from is based on the theory of the Solar Nebula. What is that you ask? Well to put it simply, it’s the belief that the birth of our solar system infused the planets with a special cloud of particles, and that cloud helped shape and define the Earth as we know it right now. Is that a little vague for you? No worries, let’s rewind back to the Big Bang, ok? I talked about in this post.

So in short, when our fraction of the galaxy was made, or more specifically when our solar system was made, our sun was born. But it wasn’t necessarily a “BOOM” and it appeared kind of moment. It was a formation of lots of gasses that turned our sun into what it is now. But…there was a lot of ‘leftovers’ in terms of the gasses that helped create it, and that “cloud” of gasses and particles was known as the Solar Nebula. It was so big that it enveloped our entire solar system, to the extent that it reached from Mercury to Pluto.

Why does that matter? Simple, a lot of gasses that were in that cloud were ones that are the building blocks of worlds…including Hydrogen. To be clear, the gas itself was harmless, it wasn’t going to threaten the worlds, just the opposite, as the gasses from the Solar Nebula got absorbed by the various planets, including Earth, they started to better form into what they are now. Which is why the outer planets have ice and not water because they’re too far away from the sun to melt. Meanwhile, the closer planets had the ability to melt, but the closer they were to the planet, like Mercury or Venus, they would burn too much, and sometimes completely evaporate.

So how does that figure into the Earth? Because of our position in the sun (the literal “goldielox” position where it was not too hot or too cold), the hydrogen and other gasses from the Solar Nebula got absorbed into our planet’s mantle. This allowed it to not just grow the Earth, but help form water inside of it. Thus helping growing the water for the Earth, even if we couldn’t see it at the time.

This particular theory has many scientists excited, because it fills in the holes of the comet/asteroid theory:

“Comets contain a lot of ices, and in theory could have supplied some water. But there’s another way to think about sources of water in the solar system’s formative days. Because water is hydrogen plus oxygen, and oxygen is abundant, any source of hydrogen could have served as the origin of Earth’s water.”

Can We Prove The Solar Nebula Theory?

Hearing some of this theory about the Solar Nebula, and all the assumptions it makes about the beginnings of our solar systems, I’m sure it seems as though this is an impossible theory. Or at the very least, impossible to prove, but you would actually be wrong in that estimation. You see, there are some scientists who have found traces of water from deep within the Earth that don’t have the heavy water hydrogen isotope levels as the comet/asteroid water. And given how deep they are within the Earth, it means that they were there long before some of the asteroids came down, which means that the Earth must have made it on its own, mainly via the Solar Nebula process.

Granted, it’s very hard to get this kind of water because of time, movement of the Earth, and just finding water that comes from the mantle:

“Even with the most pristine samples that we have, it’s not 100 percent exactly deep mantle,” Scientist Hallis says about the solar nebula created water they have found. “It’s always going to have some incorporation of the [upper] mantle in there, just because it has to travel through so much of the mantle to get to the surface.”

But if you can believe it, there’s another twist in this story.

Water On The Moon?

The moon has been above our heads for a very, VERY long time, but one of the reasons most people don’t think it’s a place we can colonize is because of the fact that the moon has no water. But…that’s not quite true. There have been recent tests on the moon that have shown that there is water on it in trace amounts. Not enough to live off of, but enough to show you that it’s there.

What’s important about this is the fact that the water traces that have been found on the moon have similar isotope traces to the kind of water found in the mantle of the Earth. Meaning…the Solar Nebula water. Which is important because the moon has long been believed to be a chunk of the Earth itself that was blasted into space via an asteroid collision (based on samples of the surface of the moon and seeing how closely it compares to Earth dirt and such).

So, if the moon has water that doesn’t have the same concentration of hydrogen isotopes the majority of the Earth from when the asteroids literally rained down…then wouldn’t that mean Earth had some water to begin with because of the solar nebula? Some seriously think so.

“Now that we are finding low values in Earth, the Moon, and Vesta, and also in the water reservoir of the asteroids, now maybe the [nebula] story is possible,” says Alice Stephant of Arizona State University, who studies Vesta. “It seems like they all share a common reservoir that is lower [in deuterium] than what we thought.”

The Certainty of Uncertainty

Here’s the thing about all of this talk of water, we honestly can’t definitively prove how much of our water came from either side of this “coin” that they’re trying to prove exists. The asteroid theory works because of the fact that we can test certain asteroids and their water content and compare it to our own. What’s more, we can prove the Solar Nebula theory because we have found pockets of water that haven’t been contaminated by the asteroids that had the heavier hydrogen isotope.

But…when it comes to proving exactly what levels of water were created by either? Yeah…we can’t really prove that. And for a very basic reason, we weren’t there when the Earth was formed, not even close! In fact, we’re SO FAR from when the Earth was created, that we could be missing a very key piece to the equation that made up the water on Earth!

That’s one of the biggest problems of trying to figure out the creation of the universe as a whole. We have to guess on a LOT of things. Such as with the asteroids that have hit Earth since its creation, or how much hydrogen MAY have been in the solar nebula when it got absorbed by the Earth and so on and so forth. The study of the beginning of our world is easily one of the ones that is a lot of guesswork, and most scientists agree that while they might just get closer to what the answer is, there’s no true way of knowing what the real answer is.

If you don’t believe me, think about other things we study on our world, like animals. Just when you think we know all the animals that exist, we find new ones ever year, or find fossils of ones we never imagined.

Water, Water Everywhere…

So where exactly does that leave us? Honestly, as a world that should be grateful for the water we have. Because no matter which way it was “filled up”, it’s still here, and because of the water cycle, we’re even more assured that water is going to continue to come. Sure, there are parts of the world with a lot of droughts, but those are the minority, not the majority.

The mystery of how the Earth got so much water remains, but the answers, the true answers, to how it all got here may just be closer to being answered than you think.

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