Washington: Earth most likely received the bulk of its carbon, nitrogen and other elements essential for life from the planetary collision that created the Moon over 4.4 billion years ago, according to a study led by Indian-origin scientists. “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,” said Rajdeep Dasgupta from the Rice University in the US.
“Ours is the first scenario that can explain the timing and delivery in a way that is consistent with all of the geochemical evidence,” said Dasgupta, co-author of the study published in the journal Science Advances. In a series of experiments, Rice University 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 sulphur-rich core.
The sulphur content of the donor planet’s core matters because of the puzzling array of experimental evidence about the carbon, nitrogen and sulphur 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. Material cycles between them” Grewal said.
One long-standing idea about how Earth received its volatiles was the “late veneer” theory that volatile-rich meteorites, leftover chunks of primordial matter from the outer solar system, arrived after Earth’s core formed. While the isotopic signatures of Earth’s volatiles match these primordial objects, known as carbonaceous chondrites, the elemental ratio of carbon to nitrogen is off.
Earth’s non-core material, which geologists call the bulk silicate Earth, has about 40 parts carbon to each part nitrogen, about twice the 20-1 ratio seen in carbonaceous chondrites. Grewal’s experiments, which simulated the high pressures and temperatures during core formation, tested the idea that a sulphur-rich planetary core might exclude carbon or nitrogen, or both, leaving much larger fractions of those elements in the bulk silicate as compared to Earth. —PTI
