Earth most likely received the bulk of its carbon, nitrogen and other life-essential volatile elements from the planetary collision that created the moon more than 4.4 billion years ago, according to a new study by Rice University petrologists in the journal Science Advances.
“From the study of primitive meteorites, scientists have long known that Earth and other rocky planets in the inner solar system are volatile-depleted,” said study co-author Rajdeep Dasgupta. “But the timing and mechanism of volatile delivery has been hotly debated. Ours is the first scenario that can explain the timing and delivery in a way that is consistent with all of the geochemical evidence.”
The evidence was compiled from a combination of high-temperature, high-pressure experiments in Dasgupta’s lab, which specializes in studying geochemical reactions that take place deep within a planet under intense heat and pressure.
In a series of experiments, study lead author and graduate student Damanveer Grewal gathered evidence to test a long-standing theory that Earth’s volatiles arrived from a collision with an embryonic planet that had a sulfur-rich core.
The sulfur content of the donor planet’s core matters because of the puzzling array of experimental evidence about the carbon, nitrogen and sulfur that exist in all parts of the Earth other than the core.
“The core doesn’t interact with the rest of Earth, but everything above it, the mantle, the crust, the hydrosphere and the atmosphere, are all connected,” Grewal said. “Material cycles between them.”
“What we found is that all the evidence — isotopic signatures, the carbon-nitrogen ratio and the overall amounts of carbon, nitrogen and sulfur in the bulk silicate Earth — are consistent with a moon-forming impact involving a volatile-bearing, Mars-sized planet with a sulfur-rich core,” Grewal said.
Dasgupta said it does not appear that Earth’s bulk silicate, on its own, could have attained the life-essential volatile budgets that produced our biosphere, atmosphere and hydrosphere. Paper. (open access) – Damanveer S. Grewal, Rajdeep Dasgupta, Chenguang Sun, Kyusei Tsuno and Gelu Costin. Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact. Science Advances, 23 Jan 2019 DOI: 10.1126/sciadv.aau3669 More.
Dasgupta, the principal investigator on a NASA-funded effort called CLEVER Planets that is exploring how life-essential elements might come together on distant rocky planets, said better understanding the origin of Earth’s life-essential elements has implications beyond our solar system.
“This study suggests that a rocky, Earth-like planet gets more chances to acquire life-essential elements if it forms and grows from giant impacts with planets that have sampled different building blocks, perhaps from different parts of a protoplanetary disk,” Dasgupta said.
“This removes some boundary conditions,” he said. “It shows that life-essential volatiles can arrive at the surface layers of a planet, even if they were produced on planetary bodies that underwent core formation under very different conditions.”
Dasgupta said it does not appear that Earth’s bulk silicate, on its own, could have attained the life-essential volatile budgets that produced our biosphere, atmosphere and hydrosphere.
“That means we can broaden our search for pathways that lead to volatile elements coming together on a planet to support life as we know it.” Jade Boyd, “Planetary collision that formed the moon made life possible on Earth” at Rice University
More likely it means we should narrow the search, and focus on planets with moons and other large, resource-rich planets in the vicinity, no?
See also: What becomes of science when the evidence does not matter?
Moon formed from smashed moonlets?
Scientists finally know how old Moon is What’s surprising, really, is how little we know about the moon in general.
And various current theories:
Another moon origin theory: Epic crash
How the Moon Formed: 5 Wild Lunar Theories (Mike Wall at Space.com, 2014)
Our moon formed in collision with embryo planet?
Origin of the moon still shrouded in mystery
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