A Collision With Another Planet Have Seeded Earth With the Ingredients for Life

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New research suggests that much of the material that made life possible on Earth arrived after a cataclysmic collision between our planet and a Mars-sized object billions of years ago—likely the same collision that produced the Moon, the scientists say.

For life to emerge on an otherwise dead planet, an assortment of chemical compounds, or volatile elements, are required, including carbon, nitrogen, and sulfur. Conventional thinking has it that Earth’s volatile elements arrived through the steady bombardment of ancient meteorites. New research published today in Science Advances proposes an alternative delivery mechanism: a catastrophic collision between Earth and a Mars-sized object, sometimes referred to as Theia, some 4.4 billion years ago. This hypothetical collision, which would have happened while our planet was still forming, seeded our baby planet with the volatile elements required for life, according to the new paper. What’s more, the lead authors of the new study, Damanveer S. Grewal and Rajdeep Dasgupta from Rice University, say it’s the same planet-on-planet collision that formed the Moon.


Artist’s depiction of a planet-on-planet collision.
Image: NASA/JPL-Caltech

For many astronomers, geologists, and astrobiologists, the notion that Earth’s volatiles arrived on the back of primitive meteorites has never been completely satisfying. Our planet, along with other rocky planets in the inner Solar System, is naturally bereft of volatiles. It just so happens that the isotopic signature of Earth’s volatiles match those seen in carbonaceous chondrites, the class of meteorites typically cited as being the deliverers of volatiles to Earth. Problem is, the volatile element ratios, such as carbon to nitrogen and water to carbon, in Earth’s silicate, mantle, crust, ocean, and atmosphere are out of whack with what’s observed in chondrites, leading to the so-called “isotope crisis” and doubts about the meteorite-seeding theory. The new study is interesting in that it offers a solution to this problem—but instead of invoking a plethora of small meteorite strikes, the authors proposed a single, gigantic collision between the Earth and an ancient planet.

The basis for this claim comes from an experiment in which the researchers attempted to mimic the conditions of this impact in the lab. The study involved high pressure and temperature experiments, along with computer simulations fed with the information gleaned from these experiments. Through this modeling work, the researchers sought to determine the size and chemical composition of the impacting planet to see how its reservoir of silicates could have mixed in with the Earth, delivering its various life-essential elements.

A depiction of the formation of a Mars-sized planet (left), and the hypothetical moon-forming collision, with the result being a planet seeded with volatiles (right). Image: Rajdeep Dasgupta

In 2016, Dasgupta co-authored a similar paper showing how the amount, or fractionation, of carbon and sulfur within the silicate of our planet could be explained by a gigantic collision with another planet. The new experiment is different in that it investigated the fate of three life-essential volatile elements—carbon, nitrogen, and sulfur—in the wake of a cataclysmic impact involving two young rocky planets, in addition to providing an estimate for the size of the hypothetical impactor.

More evidence will be required to prove the provenance of Earth’s volatiles—and also the nature of the Moon’s formation. The giant impact hypothesis, first proposed by Canadian geologist Reginald A. Daly back in the 1940s, is one of many, and the debate remains unresolved.

When asked to outline the paper’s weaknesses, Dasgupta admitted that the work was “based entirely on the geochemical behavior of elements” that didn’t include any “dynamics or physical processes involved in planetary accretion and growth.” Looking ahead, Dasgupta and his colleagues would like to do exactly this, integrating their new geochemical model with physical models.

In other words, this ain’t over yet.

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