Earth’s Carbon Could Have Arrived Later In Its Formation From The Space Between Stars

Carbon would not condense again in a form that can be trapped in the fledgling Earth, therefore having to have avoided the vaporization stage completely, coming from the interstellar medium. Image credit: NASA/JPL-Caltech

Carbon is the crucial element for life as we know it, so understanding where it came from matters a lot if we hope to understand life in the universe. New research claims that the carbon that makes us came later in the formation of Earth. The idea and supporting evidence are reported in two studies, the first one published in Science Advances.

The Sun formed from a large cloud of gas and dust. In its early days, our star influenced this material to flatten out into a disk, from which eventually the planets would form. The material in said disk is altered, vaporized, and then condensed again. And here comes the issue – carbon would not condense again in a form that can be trapped in the fledgling Earth. Earth’s carbon would therefore have to have avoided the vaporization stage completely, coming from the interstellar medium – the material between stars.

"The condensation model has been widely used for decades. It assumes that during the formation of the sun, all of the planet's elements got vaporized, and as the disk cooled, some of these gases condensed and supplied chemical ingredients to solid bodies. But that doesn't work for carbon," the lead author of this study Jie Li, a professor in the University of Michigan Department of Earth and Environmental Sciences, said in a statement.

The second work, published in the Proceedings of the National Academy of Sciences, looked at the depletion of carbon as well as sulfur from the early planetesimals. These primitive rocky bodies are what eventually merged into becoming the planets. The team used metallic meteorites to estimate how depleted of these elements the early inner solar system material might have been

"Most models have the carbon and other life-essential materials such as water and nitrogen going from the nebula into primitive rocky bodies, and these are then delivered to growing planets such as Earth or Mars," said Marc Hirschmann, professor of earth and environmental sciences at the University of Minnesota. "But this skips a key step, in which the planetesimals lose much of their carbon before they accrete to the planets."

Carbon is crucial for life, not just as building blocks but also to regulate the climate. Too much or too little could make an Earth-like planet turn uninhabitable. The researchers think that if Earth had too much carbon it would have ended up like Venus, with a deadly dense atmosphere. With too little carbon, Earth would look closer to Mars.

Hundreds of Earth-sized planets have been discovered so far in the rest of the Milky Way, so understanding the carbon balance here in the Solar System might tell us the chances of life to have arisen elsewhere.


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