Where did the water on earth come from
It is the reason we are here. It is the one substance without which no life on earth would exist. We couldn’t survive more than 3 days without it.
I’m talking about most valuable substance in the universe to mankind – H2O – Water. Water is everywhere on earth, in all its forms – gas, liquid, and solid. And this is what makes earth unique in our solar system.
Water is found on many other planets and moons, but not in all three forms.
The earth has an estimated 325 million trillion gallons of it. But here’s the mystery — earth began as a barren, lifeless, waterless ball of fire in its early history. There could not have been much water at the start. So where did all this water come from?
Join me as we go on a remarkable journey of one molecule water from the time of creation to today…coming up right now.
A single molecule of water is made up of just 3 atoms, 2 atoms of hydrogen, the most abundant substance in the universe, and one atom of Oxygen, much rarer than hydrogen but still abundant.
The journey of the first molecule of water starts almost at the beginning of time 13.8 billion years ago, at about the time of the big bang. There were no atoms formed yet, only protons and neutrons.
It took about 400,000 years for the universe to cool down enough for electrons to be captured in orbits around protons. And this is what formed the first atom, simply one electron one proton. This was hydrogen.
It’s just one proton with a positive charge that has captured one electron with a negative charge. One electron spinning around in a fuzzy cloud of probability around one proton.
So this is how the first 2 atoms of our 3 atom structure of water came about. The oxygen portion of water had a much longer journey.
Oxygen is a much heavier and more complicated atom than hydrogen. It has 8 electrons orbiting a nucleus consisting of 8 protons and 8 neutrons.
It took about another billion years or so before the first oxygen atoms were formed because it required nuclear fusion – this is literally when smaller atomic nuclei like hydrogen and helium fuse together to form a heavy nucleus like that of oxygen.
This kind nuclear fusion can only occur in nature, in the heart or center of stars.
The earliest stars were massive, much more massive than our sun. But this also made them short lived.
And about 600 million years after the big bang is when some of the first stars began to go supernova, but just before these massive supernova explosions, in their core, lighter atoms fused to form heavier atoms like oxygen, carbon, and others.
When these stars blew up in huge supernova explosions, the oxygen and other heavier elements began to disperse into space and spread out – helped by the force of the explosion and solar winds.
When this spewed oxygen mixed or comingled with hydrogen, and an energy source of some kind, perhaps heat from a nearby stellar explosion or lightening. Yes, there can be lightening in space. Hydrogen and Oxygen with the help of some energy, fused together to form Water.
After formation of this water, it turned to ice in the coldness of space and mixed with other dust particles that were simply floating in space for eons of time. And when enough dust from multiple supernova explosions collected over time in one spot, the gravitational pull of all this matter began to coalesce and collapse into another generation of stars. The leftover dust from the star formation coalesced into planets, planetesimals, asteroids and comets.
So you would think that since water coalesced into planets, our planet would have had all the water it has today from its early beginning. But it turns out that the most recent evidence shows that this was probably not the case, because earth had huge cosmic impacts.
One of these was a colossal impact with another early planet the size of Mars called Theia. Theia collided with earth and essentially turned it into one giant piece of molten rock. The debris from this collision is what eventually created our moon by the way.
The heat and violence of this collision would have evaporated most of the water on earth. While some of it probably remained due to gravity, a lot of the water would have spewed back out into space. So most scientists believe that the massive amount water we see on earth today must have come from another source, long after earth was formed.
Up until recently, most scientists thought that the most likely water delivery candidates were comets.
You might be familiar with comets. Comets like the 1995 Hale-Bopp and or 1986 Haley’s are full of water. They are best described as dirty snowballs. In fact water is what causes the huge tail pf comets that you can observe from earth. The frozen water evaporates as it gets closer to the sun.
But in 2012, researchers found that the chemical make up of the water on Comets doesn’t fit with the chemical make up of the water on earth.
What chemical make up did they measure? They measured the ratio of hydrogen isotopes deuterium and protium. It turns out all water has a very tiny component of radioactive isotopes of hydrogen deuterium and Protium.
This is normal and is not harmful to us. The levels of these isotopes on comets is twice what we find on earth.
So how then was the water delivered to earth? Well it turns out that the source was from objects much closer to earth than comets which live extremely far way in a formation called the the Oort cloud.
The source of earth’s water is most likely Your every day humble asteroid, you know like the one that killed the dinosaurs 65 million years ago. It turns out that early asteroids had huge amounts of water too, since they had not been exposed to the heat of the sun for as long as they have now.
The isotope ratios of near earth asteroids, wouldn’t you know it, matches almost perfectly with the isotope ratios in water that we find on earth.
So it turns out that the dinosaur-killing asteroid was not the only one that hit the earth. Many such asteroids, probably hundreds of thousands of them hit the earth early in its history.
This period even has a name. It is called the late heavy bombardment period, and it happened about 3.8 billion years ago, about 600 million years after earth’s formation.
And these asteroids were formed from the same dust, ice and other substances as the early earth – which came from multiple supernova explosions over billions of years since the beginning of the universe.
So the next time you drink a glass of water, think about the journey that every single molecule of that water has taken, from the center of stars to floating among dust clouds for billions of years in space, to the formation of asteroids, to its collision on earth, to the formation oceans, to evaporation into clouds, to rain into rivers, to your bottle and into your body.
If that molecule could only talk it would tell you an amazing story.
A normal water molecule is made of two hydrogen atoms and one oxygen atom. In heavy water, a normal hydrogen atom is replaced with deuterium, which is like hydrogen except that it has an extra neutron in its nucleus.
To see if comets might be the source of Earth’s water, in 1986, the ESA probe Giotto flew by Halley’s Comet, becoming the first spacecraft to make close observations of a comet. It discovered that Halley’s Comet had twice the amount of heavy water compared to normal water as Earth does.
Halley’s Comet comes from the Oort Cloud, a giant spherical cloud of trillions of icy bodies that extends from 5,000 to 100,000 times the distance of Earth to the sun. The data from Halley’s Comet and from other Oort Cloud comets “ruled out Oort Cloud comets as being the source of terrestrial water,” said lead study author Kathrin Altwegg,of the University of Bern in Switzerland, principal investigator for the ROSINA mass spectrometer on Rosetta. [Fun Facts about Comets]
But the Oort Cloud is not the only source of comets in the solar system. Another home to the dirty snowballs is the disc-shaped Kuiper Belt, which extends from about 30 to 55 times the distance of Earth to the sun. In 2011, data from ESA’s Herschel Space Observatory revealed that Kuiper Belt comet 103P/Hartley 2 had a deuterium-to-hydrogen ratio “that matched terrestrial water’s perfectly,” Altwegg said during a news conference Tuesday (Dec. 9). “The Hartley 2 measurement — that was a real big surprise.”
“Today’s asteroids have very little water — that’s clear,” Altwegg added. “But that was probably not always the case. During the Late Heavy Bombardment 3.8 billion years ago, at that time, asteroids could have had much more water than they could now.” [Comet Quiz: How much do you know about comets?]
The asteroids seen now “have stayed in the vicinity of the sun for 4.6 billion years,” Altwegg said. “They’ve lost water due to the sun, due to heat. But to start with, they might have had much more water than they have now.” Future analysis of ice-rich bodies in the asteroid belt could shed light on whether Earth’s water really did come from there, Altwegg said.
