When people think about the most important ingredient for life on other planets, they usually talk about water. But there’s another element that makes our existence possible.
“We’re carbon-based life forms,” said University of Chicago geophysical scientist Fred Ciesla, “and carbon is an important part of keeping a mild climate.”
It can also be used as forensic tool to piece together how the earth and solar system must have formed. In two papers, Ciesla and colleagues at California Institute of Technology, the University of Michigan and the University of Minnesota laid out a history of carbon in the formation of the solar system.
By examining carbon, the scientists found that a large fraction of the Earth's building blocks probably formed soon after the solar system did—within the first million years, much earlier and more precise than the previous estimate of sometime within the first 150 million years. This discovery may also inform the search for life elsewhere in the galaxy.
The devil in the details
Even within our home system, questions still surround the formation of the Earth and our sibling planets. The prevailing theory is that the solar system began as a giant cloud of hot gas and dust that coalesced into the sun; then, gradually, pieces started to clump together into planets as the whole thing cooled down.
But the planetary devils are in the details. Each element behaves differently based on the conditions it was experiencing at the time, so scientists can examine today’s molecules to find clues about what that environment was like back then—similar to how a footprint looks different if it’s made in soft mud after a rain, versus after a dry spell. This back-tracing has been done extensively for other elements, but less so for carbon.
By tracing the history of carbon this way, the team found a gap in the theory.
One of the papers, led by Jie (Jackie) Li of the University of Michigan, estimated the total amount of carbon that could possibly be contained within the Earth. The research found that, relatively speaking, the planet has just a little bit of carbon. While this amount of carbon is just right for life on Earth—enough to trap some heat from the sun, but not so much that the heat bakes the planet like it does on Venus—this Goldilocks amount of carbon is difficult to explain under the existing theory, which better accounts for either no carbon or a lot of carbon.