An ancient collision might explain a longstanding mystery about how Earth collected the ingredients for life
Until now, scientists thought that it took hundreds of millions of years after our solar system formed for Earth to pick up these ingredients. But a group of scientists at Rice University just came out with a study that suggests at least a couple of these ingredients might have come along much sooner.
"The question is: is there no possible scenario in which carbon could have come to our planet during the main phase of planet formation?" Rajdeep Dasgupta, Rice geologist and co-author of the new study, told Business Insider.
Turns out, there is a possible scenario indeed. And it involves a massive, ancient explosion.
The recipe for life
Think about the things you need to properly exist. On one level, there's water, food, air, your phone maybe. But when you break that down you get oxygen, hydrogen, nitrogen, calcium, phosphorus, and carbon. This is what 99% of your body is made of - these are the elements that conspire together to maintain your existence.
So imagine we take away some of these elements. Let's pick one of the more volatile elements, like carbon. Imagine we go back in time 4.5 billion years to when Earth was just a baby and we strip it of all its carbon: We burn up all of the carbon in Earth's atmosphere and lock away what's left deep inside its core. Then what happens?
Probably nothing. Literally nothing - life on Earth doesn't form and our special planet remains just another lifeless speck in the ever-expanding universe.
That's because as far as we know, life doesn't form without carbon. Not only is carbon the most abundant element on Earth, it has the miraculous ability to cluster together in branches that other molecules latch onto - it's the central building block that allows for the complex molecular structures necessary for life.
But scientists argue that in the early days of Earth's long life, this was exactly the case. They say that most of baby Earth's carbon would have either evaporated into the void of space or become trapped in its metallic core.
So the question is: Where did all of our carbon - the carbon that all known life is based on - come from?
Many scientists believe that it was delivered to us hundreds of million years after the formation of the solar system by meteorites.
"It's as if you are dusting the planet after the core of it formed with some small amount of goodies that bring in all of these important elements," Dasgupta said.
But there's a problem with this hypothesis. Although it might explain the overwhelming abundance of carbon on Earth, it doesn't account for the ratio of carbon to other elements, like sulphur and nitrogen.
Now, the scientists at Rice University think they might have a different answer that addresses this problem. And it involves a 4.4 billion year old collision in which baby Earth devoured an embryonic, Mercury-like planet.
The scientists had been studying how carbon would behave if it had been present during Earth's early formation, the main phase of its accretion. During this process, scientists imagine there was an ocean of silicate magma, and all the denser metallic liquid would have sunk through the ocean to eventually form Earth's metallic core. They found that if carbon was present at that time, it all would have gotten trapped in our planet's iron core, leaving almost nothing available to its mantle, crust, and atmosphere.
And yet, right now, carbon is the most abundant element on our planet.
The scientists wondered if this carbon-trapping core is the case on all terrestrial planets in the magma ocean stage.
And it turns out, it's not. If the iron-rich core of a planetary body also has a significant amount of sulphur or silicon, it actually expels carbon, meaning there might be a significant concentration of carbon in its outer portions.
Earth eats planets like Mercury for breakfast
In fact, our solar system's very own Mercury has many of these properties - its core is thought to be relatively silicon-rich while its surface looks to be much more carbon-rich compared to other planetary bodies.
"We sort of joined the two dots,'" Rajdeep said. "We saw that one way to then bring carbon to our planet would be a merger or collision between Earth and a planetary embryo similar to Mercury."
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"This points to the origin of carbon as an element in our planet," Rajdeep said. "It basically sets the stage for any future development of carbon based life."
A new framework for the scientific community
But he was quick to point out that the study doesn't directly address the formation of life, but rather it offers an explanation about how life sustaining elements such as carbon and sulphur arrived at our planet.
"Of course, you need many other factors to line up and work in tandem for elemental carbon to give to rise to the right molecules to foster life," Dasgupta said. "This study is not about that. It just says at least the ingredients to make the right recipe for life were available early on, and you didn't need to rely on much later additions brought by asteroids."
Dasgupta admits that the study, which provides a very different view of the origin of volatile elements like carbon, is going to be provocative, and many future studies will have to be done to build up more evidence for the hypothesis. He added that aside from the abundance of carbon and sulphur, there are many other volatiles that need to be explained. For example, he said, many people wonder how water was delivered to our planet, and how nitrogen was behaving during these types of processes.
"What's exciting about this study is that it provides a very different framework for the scientific community to think about how volatiles might have acted during Earth's formation," Dasgupta said. "Many more studies will follow to try to tease out the details or other possibilities."