Giant Oxygen Explosions Could Have Set the Stage for Life on Earth

Dynamics deep in Earth's core could have helped trigger the first life. Hector Guerrero/AFP/Getty Images

Life is in just a tiny thin layer above Earth's surface—but it may only exist because of processes happening deep inside the planet, according to a new paper published in the journal National Science Review.

The paper looks at what's happening between the Earth's outer core and its mantle, two regions of molten rock where old crust goes to be recycled into new seafloor and continents. In particular, the team wanted to understand what was happening with water in this region, since they know there's almost as much water locked inside Earth as filling its oceans.

That water sinks, locked within rock that then melts and sets the water free within the core. There, the water is torn apart by iron, which snatches up the oxygen atoms and leaves the hydrogen atoms to flee, rising through Earth's layers. What's left below is a compound called iron dioxide, which crystallizes—at pressures of up to 1 million times that found at the Earth's surface and temperatures above 3,500 degrees Fahrenheit.

"Based on our knowledge of the chemical makeup of the slabs that are drawn into the Earth's deep interior by plate tectonics, we think 300 million tons of water could be carried down to meet iron in the core and generate massive iron dioxide rocks each year," lead author Ho-kwang "Dave" Mao, a geologist at the Carnegie Institution for Science in Washington, D.C., said in a press release.

The new paper is a review looking over all the science in the field so far and trying to piece together a comprehensive picture of where water moved and in what volumes a very long time ago very deep below the surface, which means that it's very difficult to determine whether a hypothesis is actually valid.

The team looked back at the history of Earth to trace what might have been happening in two separate types of ocean: the above surface water type, which likely formed about 4.5 billion years ago, and the below-surface magma type. Specifically, they wanted to calculate how much water was where at any given times.

But it was the oxygen-rich rocks that water creates that was the particularly intriguing piece for the scientists. That's because those giant slabs of oxygen-rich rock, under the right geological circumstances, could quickly erupt, spewing oxygen into the atmosphere.

And that, in turn, is a new possible explanation for what scientists call the Great Oxygenation Event, a sudden spike in levels of the gas in Earth's atmosphere that took place between 2 and 2.5 billion years ago. Previously, scientists have attributed that oxygen to a population boom among photosynthetic bacteria. The new paper doesn't invalidate that hypothesis, it just offers an alternative possibility.