Privileged Planet: much of our water present at start (Introduction)

by David Turell , Saturday, December 17, 2022, 15:14 (497 days ago) @ David Turell

Latest study using deuterium analysis:

https://www.sciencealert.com/scientists-have-figured-out-just-how-old-our-water-is-and-...

"A research article in GeoScienceWorld Elements shows that other young solar systems have abundant water. In solar systems like ours, water is along for the ride as the young star grows and planets form. The evidence is in Earth's heavy water content, and it shows that our planet's water is 4.5 billion years old.

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"The formation of a solar system starts with a giant molecular cloud. The cloud is mostly hydrogen, water's main component. Next are helium, oxygen, and carbon, in order of abundance.

"The cloud also contains tiny grains of silicate dust and carbonaceous dust. The research article takes us through the history of water in our Solar System, and this is where it starts.

"Out here in the cold reaches of a molecular cloud, when oxygen encounters a dust grain, it freezes and adheres to the surface.

"But water isn't water until hydrogen and oxygen combine, and the lighter hydrogen molecules in the cloud hop around on the frozen dust grains until they encounter oxygen.

"When that happens, they react and form water ice – two types of water: regular water and heavy water containing deuterium.

***

"100 K is bitterly cold in Earthly terms, only -173 degrees Celsius. But in chemical terms, it's enough to trigger sublimation, and the ice changes phase into water vapor. The sublimation occurs in a hot corino region, a warm envelope surrounding the cloud's center.

"Though they also contain complex organic molecules, water becomes the most abundant molecule in corinos.

"Water is abundant at this point, though it's all vapor. "… a typical hot corino contains about 10,000 times the water in the Earth's oceans," the authors write.

"That's step two in the process outlined by the authors, and they call it the protostar phase.

***

"But now, the water molecules in that icy mantle contain the history of the water in the Solar System. "Thus, dust grains are the guardians of water inheritance," the authors write.

"That's step three in the process.

"In step four, the Solar System begins to take shape and resemble a more fully-formed system. All the things we're accustomed to, like planets, asteroids, and comets, start forming and taking up their orbits. And what do they originate from? Those tiny dust grains and their twice-frozen water molecules.

***

"Water from the first synthesis is 4.5 billion years old, and the question becomes, "How much of that ancient water reached Earth?"

"To find that out, the authors observed the only two things they could: the amount of water overall and the amount of deuterated water.

"As the authors put it, "… namely, the ratio of heavy over normal water, HDO/H2O."

***

"So they know that Earth's heavy water abundance, the HDO/H2O ratio, is about ten times greater than in the Universe and at the beginning of the Solar System.

'"'Heavy over normal' water on Earth is about ten times larger than the elemental D/H ratio in the Universe and consequently at the birth of the Solar System, in what is called the solar nebula," the authors explain.

"The results of all this work show that between 1 and 50 percent of Earth's water came from the initial phase of the Solar System's birth. That's a wide range, but it's still a significant piece of knowledge."

Comment: note my bold. Why should the Earth have so much extra Deuterium? Was our water supply especially directed? Huge explanatory article.