What was Earth like in its infancy? Scientists have long believed that it was a brutally hot and hellish place, covered in molten rock and pelted by asteroids--no wonder the 600-million year period that began 4.6 billion years ago is called the Hadean Eon, after Hades.
But surprising new research conducted at Vanderbilt University suggests that picture may be a bit off. It indicates that the conditions on Earth during its first 500 million years were actually similar to those on the Earth we know today.
Study co-author Calvin Miller at the Kerlingarfjoll volcano in central Iceland. Some geologists have proposed that the early Earth may have resembled regions like this.
The study builds upon previous research on tiny minerals known as zircon crystals. As new layers form around the cores of these durable crystals, the crystals "record" the history of various geological events a bit like a time capsule--making them a good tool for looking back at Earth's geological history.
The previous research indicated that early Earth may have been covered with liquid water and a rocky crust, potentially hospitable for life. But scientists continued to debate just how similar the early Earth was to modern-day Earth, and whether early Earth had full oceans and continents.
For the new study, scientists analyzed more than 1,000 zircon crystals collected in Iceland, dating from 15 million years ago to the present. Then they compared these younger crystals to zircons found in Western Australia that date back 4.3 billion years.
Images of Icelandic zircons taken with a scanning electron microscope. They range in size from 0.1 millimeter to a few thousands of a millimeter.
“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,” study co-author Calvin Miller, a professor of earth and environmental sciences at the university, said in a written statement.
What did the comparison show? Trace elements and isotopes in the zircons revealed that the magmas in which the younger Icelandic zircons grew were much hotter than those of the ancient Hadean zircons.
"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," Miller said in the statement. In such an environment, continents and oceans may have been able to form.
In other words, it may be time to rewrite the geology textbooks.
The study was published online this week in the journal Earth and Planetary Science Letters.