Albert McKeon

Jul 12th 2019

A Planetary Collision Might Have Started Life on Earth


A recent study about the beginnings of Earth gives us our own Big Bang theory.

Rice University scientists propose that a planetary collision might have led to the formation of Earth and its inhabitants. A planet the size of Mars smacked into a mostly rocky Earth 4.4 billion years ago, the scientists posit, leaving behind elements that not only shaped our world but also us. As a bonus gift, debris from the crash floated into space and created the moon.

Reaching their hypothesis through chemical experiments and computer modeling, the researchers add to the scientific theories behind creation, not to mention the larger philosophical conversation about the randomness of it all. If that planet had veered just a bit to the right of Earth and kept traveling, would we be here today?

Questions About How It All Began

The scientists’ main theory is equally remarkable and revolutionary. In a nutshell, their research, which appeared in the January issue of ScienceAdvances, holds that Earth’s status as the only known life-sustaining planet came about because another planet that carried carbon, nitrogen, sulfur and other elements just happened to be passing through our neighborhood and had an accident. Essentially, they’re suggesting that if not for this collision, Earth might have remained an uninhabitable wasteland.

And it’s not just the randomness of the planets colliding that’s striking. It might be nothing short of miraculous that the traveling planet, essentially a meteorite, happened to carry what scientists call “volatile-rich” elements from a disk in space that holds planet building-block materials.

“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,” one of the research paper’s co-authors, Rajdeep Dasgupta, told the Rice University news department.

Scientists had long suspected that Earth’s volatile elements had arrived because of a collision with some sort of meteorite that served as a carrier of the building blocks, but they disagreed on how it happened. “Ours is the first scenario that can explain the timing and delivery in a way that is consistent with all of the geochemical evidence,” Dasgupta said.

A Collision With Big Consequences

As the science writer Marc Kauffman neatly summarizes on his blog Many Worlds, some of the researchers’ theories rest on their finding of a similarity between the nitrogen and hydrogen compositions seen in lunar gasses and in the bulk silicate portions of Earth. “Carbon, nitrogen and sulfur are deemed volatile elements because they have a relatively low boiling point and can easily fly off into space from planets and moons in their early growing stages,” Kauffman wrote.

And that’s what happened, the Rice scientists say, when the Mars-shaped planet met up with Earth. They reached this theory by simulating the high pressures and temperatures of the donor planet during its core formation, a step taken to see if its sulfur-rich core could possibly not include carbon and nitrogen. Not having those two elements in the core is an important aspect of the research. The simulations showed carbon and nitrogen were, in fact, on the planet’s rocky surface, or were placed even higher, thus making it easier for them to mix with Earth during a collision.

The scientists then ran a computer simulation to discover how such a collision would transform Earth from a lifeless rocky planet to one that suddenly held the elements that create life. Reaching an answer required varying the many starting conditions after a collision, which meant the scientists had to run about 1 billion computer scenarios and compare them to the known conditions of today’s solar system, according to the Rice University news story.

“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,” researcher Damanveer Grewal told Rice University news.

With that statement, Grewal not only explains how his team’s research led to their theory about the formation of Earth but, as their research paper details, he also claims the debris from the planetary collision floated into space and eventually coalesced to form our moon.

New Thoughts on Life as We know It

As Kauffman points out in his blog post, the Rice University researchers don’t dive deep into the reasons why water appeared on Earth, but they hold out the opinion that the gift-bearing planet probably delivered other volatiles.

The origin of water on this planet is worth researching another day. For now, the Rice University study is worthy of contemplation and a trigger for deeper thoughts about how we’re on our planet today.