The origin of life on Earth is one of the biggest mysteries that science has yet to decipher. A team of scientists from Rice University in Texas believe that they have finally found a possible answer, Phys.org is reporting.
In a new study published on Wednesday in the journal Science Advances, the researchers argue that our planet was seeded with the ingredients for life after a violent cosmic collision in its distant past. According to their analysis, it was the encounter with Theia — the Mars-sized alien planet that crashed into Earth some 4.5 billion years ago, giving birth to the moon — that delivered the key chemical elements necessary for life to spark on our planet.
Aside from spawning the moon by breaking off a chunk of Earth and sending it careening into space, the epic collision with Theia also brought to our planet a large number of volatile elements, such as carbon, nitrogen, and sulfur. These ignited the spark of life by interacting with the bulk silicate Earth, thereby enabling the planet to spring to life, explains a news release from Rice University.
"Earth's status as the only life-sustaining planet is a result of the timing and delivery mechanism of carbon, nitrogen, sulfur, and hydrogen," the authors wrote in their paper.For a long time, scientists have speculated that these volatiles appeared on Earth as a result of a long string of asteroid impacts. Based on their isotopic composition, these chemical elements are believed to have derived from carbonaceous chondrites — a type of primitive carbon-rich meteorites that originated in space.
"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, a geologist at the university.
Since these meteorites are far richer in volatiles than the planets of the solar system, it made sense that carbonaceous chondrites were the source of these chemical elements on Earth. However, after studying the ratio of volatiles in chondrites, Dasgupta and his colleagues uncovered that the carbon-nitrogen ratio of the bulk silicate Earth is over 20 times the ratio seen in the meteorites.
This made them wonder whether Earth's volatiles may have come from another source. To find an answer to this question, the team devised a series of experiments to see if these chemicals could have arrived on Earth following the collision with a planet that has a sulfur-rich core — similar to Theia.
The scientists used capsules filled with silicate and alloy mixtures and simulated the extreme high-temperature, high-pressure conditions that led to the formation of Theia's core. This enabled them to calculate at what percentage of sulfur the core might have excluded carbon and nitrogen, leaving them in the planet's bulk silicate, details Science Alert.The next step was to run a series of computer models in order to narrow down the timing of volatile delivery. The team tested around 1 billion different scenarios, which eventually pointed to the collision with Theia.
"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," said study lead author Damanveer Grewal, a petrologist at the university.
While this doesn't exclude the contribution of carbonaceous chondrites, it does show that the impact with Theia was essential in delivering life-forming volatiles to Earth.
"The timing and mechanism of volatile delivery has been hotly debated," said Dasgupta.
"Ours is the first scenario that can explain the timing and delivery in a way that is consistent with all of the geochemical evidence."