Crystals Reveal Early Earth Wasn't as 'Hellish' as Previously Thought

Early Earth was a hellish place to be, according to conventional theories. About 500 million years after it formed, our planet was completely hostile to life and covered by a giant "magma ocean"--at least that's what scientists thought. Now, new evidence in the form of zircon crystals have hinted otherwise, showing that Earth had conditions that were more similar to those found today.

About 30 years ago, researchers discovered zircon crystals, which is a mineral typically associated with granite, with ages exceeding 4 billion years old preserved in younger sandstones. These crystals actually had the potential to tell scientists a bit more about Earth's earliest crust. They showed that early Earth didn't have a magma ocean, but instead had a solid crust and liquid water. Yet researchers have long debated how similar this ancient Earth was to the Earth of today.

In the end, two schools of thought emerged. One argued that the ancient Earth was similar to the one of today. The other argued that while Earth wasn't nearly as hostile as once believed, it was still a foreign and hostile place.

That's why the researchers decided to investigate this time period, called the Hadean period, a bit more closely. They believed that the answers lay in zircon crystals from different locations.

"We reasoned that the only concrete evidence for what the Hadean was like came from the only known survivors: zircon crystals-and yet no one had investigated Icelandic zircon to compare their telltale compositions to those that are more than 4 billion years old, or with zircon from other modern environments," said Calvin Miller, one of the researchers, in a news release.

The scientists analyzed about 1,000 zircon crystals for their age and elemental and isotopic compositions. Then, they searched for all comparable analyses of Hadean zircon and for representative analyses of zircon from other modern environments. In the end, they found that Icelandic zircons were distinctive from crystals formed in other locations on modern Earth. In fact, it turns out that Icelandic zircons grew from much hotter magmas than Hadean zircons.

"Our conclusion is counterintuitive," said Miller. "Hadean zircons grew from magmas rather similar to those formed in modern subduction zones, but apparently even 'cooler' and 'wetter' than those being produced today."

In other words, Hadean Earth was probably a lot more like modern Earth than previously thought.

The findings are published in the journal Earth and Planetary Science Letters.