Did Ancient Planet Collision Allow Life to Thrive?

Artist's impression of a Mercury-sized body that smashed into Earth early in the solar system's history.

When a Mercury-sized body smacked into the young Earth 4.4 billion years ago, the cosmic collision likely made carbon more available for life to thrive today, a new study suggests.

The finding would explain a paradox puzzling scientists, which is how our planet still has carbon on the surface when it should have disappeared long ago. Theories suggest that early carbon on the surface would have boiled into space, or would have been stuck in the planet's core.

"The challenge is to explain the origin of the volatile elements like carbon that remain outside the core in the mantle portion of our planet," said Rajdeep Dasgupta, who co-authored the study with lead author and former Rice postdoctoral researcher Yuan Li, in a statement.

Previously, some studies suggested the carbon could have come from meteorites, which are small rocks that whiz around the solar system and occasionally crash into Earth. But further study revealed some problems with the theory.

"The problem with that idea is that while it can account for the abundance of many of these elements, there are no known meteorites that would produce the ratio of volatile elements in the silicate portion of our planet," said Li, who is now a staff scientist at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.

The key was imagining a different type of core composition from the Earth, based on updated studies of Mercury and Mars in past decades. These other planets suggested that perhaps our core may be more complex than just iron and nickel and carbon.

How a young Earth could have merged with a Mercury-sized object when the two collided about 4.4 billion years ago. "Magma ocean processes could lead planetary embryos to develop silicon- or sulfur-rich metallic cores and carbon-rich outer layers," Rice University wrote in a statement.

Mars is believed to have a lot of sulfur in its core, and Mercury likely contains a lot of silicon. The research team tested different elements in a lab that squeezes rocks in hydraulic presses, mimicking the high-pressure and high-temperature conditions below Earth's surface.

Read more at Discovery News