A common theory holds that the building blocks for life came to Earth from comets that landed here billions of years ago. But what if they also came from within the planet?
A study published last month by Johns Hopkins University professor Dimitri Sverjensky suggests that organic compounds are pulled beneath Earth's crust when tectonic plates collide, dissolving in water that travels through the mantle hundreds of miles below the surface. The carbon-based material might provide food for subterranean microorganisms, cause diamonds to form and, sometimes, make its way back to the planet's surface blasted out of volcanoes.
The findings could contribute to new understanding of how life formed on Earth's surface. But before that, they represent an important step in the study of what is happening at depths farther than any drill can dig, scientists said.
Little is known about the physics and chemistry of materials interacting at pressures tens of thousands of times greater than that of Earth's atmosphere. But research like Sverjensky's is expected to start explaining it better in the coming years.
"Calculations under pressure are more difficult because we have less experimental data to basically come up with good models," said Giulia Galli, a professor of molecular engineering at the University of Chicago who also works in Sverjensky's field. "What he's doing is a big step forward in understanding the materials under pressure in the Earth."
Sverjensky's research paper, written with Vincenzo Stagno of the Carnegie Institution in Washington and Hopkins graduate student Fang Huang, is among the first to apply a new model capable of such understanding. Sverjensky and others at Carnegie spent years developing the model, publishing it a year ago.
At depths of 100 kilometers or more, water doesn't behave the way it does on the surface or within Earth's crust, Sverjensky explained. It contains hydrogen ions and other charged particles that generate chemical reactions as they meet layers of varying rocks and minerals in the Earth.
When one tectonic plate slides beneath the edge of another, generating earthquakes on the surface, it carries with it carbon-based materials that meet molten rock. It all gets "cooked,"dissolving into water that filters up toward the crust, interacting differently with materials as it passes through the mantle, Sverjensky said.
But it wasn't until the new model, known as the Deep Earth Water model, was developed that geochemists like Sverjensky could understand just how much of the carbon-based materials are contained in the fluids. It's likely so much that the fluids are like vinegar, containing acetates, substances that are commonly broken down by organisms in nature, he found.
That could be a telling finding, because it suggests that when those acetates reach levels where microorganisms are present, they could serve as "food" for the organisms, broken down into things like carbon dioxide and methane, Sverjensky said. The carbon-based compounds that go into life building blocks like amino acids and RNA also can get pulled up to the surface through volcanic eruptions.
They also could contribute to diamond formation, helping to explain why in some cases, the gemstones contain pockets of minerals that can show scientists what kinds of materials are present at depths farther than we are capable of drilling, currently less than 10 miles.
"It seems pretty unlikely we're ever going to have drill holes that go a huge amount deeper," Sverjensky said. "It's enormously important for understanding the deep earth carbon cycle and the kinds of rocks and minerals at depth in the Earth."
As the geochemistry research community tries other applications of the new high-pressure water model, it should shed more light on a field of Earth science about which relatively little is known. That includes questions about how the water and the compounds it carries react when they meet different boundaries of rocks and minerals in the Earth, Galli said. And scientists also hope to gather more data at different ranges of pressure and temperature to broaden the utility of the new model, she said.
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"That's what governs the long-term habitability of the planet," he said. "Over the hundreds of millions of years where we've had life on Earth, the habitability has been governed by carbon dioxide in the atmosphere."