Home Space Planetary collision that formed the moon made life possible on Earth

Planetary collision that formed the moon made life possible on Earth

Planetary delivery explains enigmatic features of Earth’s carbon and nitrogen.

A new study by the Rice University scientists suggests that most of the Earth’s essential elements of life such as carbon, nitrogen and other life-essential volatile elements, came from the planetary collision that created the moon more than 4.4 billion years ago.

Study co-author Rajdeep Dasgupta said, “From the study of primitive meteorites, scientists have long known that Earth and other rocky planets in the inner solar system are volatile-depleted. 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.”

Scientists compiled the evidence from a combination of high-temperature, high-weight tests in Dasgupta’s lab, which spends significant time in examining geochemical reactions that occur profound inside a planet under extreme 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.

Grewal’s trials, which reproduced the high pressures and temperatures amid core formation, tried that a sulfur-rich planetary center may exclude carbon or nitrogen, or both, leaving a lot bigger divisions of those components in the mass silicate when contrasted with Earth. In a progression of tests at a scope of temperatures and pressure, he analyzed how much carbon and nitrogen made it into the center in three situations: no sulfur, 10 percent sulfur, and 25 percent sulfur.

He found that the Nitrogen was largely unaffected. It remained soluble in the alloys relative to silicates and only began to be excluded from the core under the highest sulfur concentration.

On the other hand, Carbon was considerably less soluble in alloys with intermediate sulfur concentrations, and sulfur-rich alloys took up about 10 times less carbon by weight than sulfur-free alloys.

Using the information, scientists designed a computer simulation to find the most likely scenario that produced Earth’s volatiles. Finding the answer involved varying the starting conditions, running approximately 1 billion scenarios and comparing them against the known conditions in the solar system today.

Grewal said, “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.”

Scientists are now exploring how life-essential elements might come together on distant rocky planets to better understand the origin of Earth’s life-essential elements has implications beyond our solar system.

Dasgupta said, “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.”

“This removes some boundary conditions. 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.”

“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.”

A schematic depicting the formation of a Mars-sized planet (left) and its differentiation into a body with a metallic core and an overlying silicate reservoir. The sulfur-rich core expels carbon, producing silicate with a high carbon to nitrogen ratio. The moon-forming collision of such a planet with the growing Earth (right) can explain Earth’s abundance of both water and major life-essential elements like carbon, nitrogen and sulfur, as well as the geochemical similarity between Earth and the moon. (Image courtesy of Rajdeep Dasgupta)
A schematic depicting the formation of a Mars-sized planet (left) and its differentiation into a body with a metallic core and an overlying silicate reservoir. The sulfur-rich core expels carbon, producing silicate with a high carbon to nitrogen ratio. The moon-forming collision of such a planet with the growing Earth (right) can explain Earth’s abundance of both water and major life-essential elements like carbon, nitrogen and sulfur, as well as the geochemical similarity between Earth and the moon. (Image courtesy of Rajdeep Dasgupta)

Additional co-authors on the Science Advances study are Kyusei Tsuno and Gelu Costin, both of Rice. The research was supported by NASA, the Deep Carbon Observatory and the David and Lucile Packard Foundation.

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