Until the 1980s, geologists agreed that early Earth (known as the Hadean period) was not conducive to life. Geologists couldn’t find any rock formations dating back to the period and concluded early Earth was either completely molten or suffered from continuous asteroid bombardment. Earth was believed to be one giant pool of magma.

That view began to change around 30 years ago when geologists spotted zircon crystals dating back more than 4 billion years old.

This week, a study was published by a team of geologists led by Calvin Miller, the William R. Kenan Jr. Professor of Earth and Environmental Sciences at Vanderbilt University. It was published in the journal Earth and Planetary Science Letters.

Besides dating the crystals, Miller and his team used other methods to determine temperature and if water was present.

zircon crystals

What did they find? Early Earth wasn’t some dimension of hell as previously thought. At least, not all the time. During certain periods, the Earth had a crust cool enough for water to form. There may have even been oceans such as the ones we have today.

While most geologists see that early Earth wasn’t as bad as previously thought, there’s still debate over how bad it was. Some think early Earth looked a lot like it does today. Others believe it was still an extremely hostile place for life.

In order to get a better picture, Miller and his team looked at Iceland.

“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 Miller in a statement.

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Tamara Carley, a Vanderbilt doctoral student and assistant professor at Lafayette College, collected samples in Iceland and separated thousands of zircon crystals from them.

“We discovered that Icelandic zircons are quite distinctive from crystals formed in other locations on modern Earth. We also found that they formed in magma that are remarkably different from those in which the Hadean zircons grew,” said Carley.

They found the zircons in Iceland formed from magma a lot hotter than the zircons in the Hadean period.

Miller concluded, “Hadean zircons grew from magma rather similar to those formed in modern subduction zones, but apparently even ‘cooler’ and ‘wetter’ than those being produced today.”

Image credit: Martin Rietze. Tamara Carley / Vanderbilt

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