Earth was formed about 4.5 billion years ago. For decades, scientists believed that conditions on early Earth were utterly hostile to life. They thought it was hellishly hot, constantly bombarded with asteroids. It was entirely molten, and the surface was covered with a “magma ocean.” But an alternate view, backed by solid evidence, suggests that conditions on our planet for the first 500 million years after its formation could have been similar to the present day.
Hadean period lasted about 500 million years
According to a new study conducted by researchers at Vanderbilt University, the early Earth may have been complete with oceans, crustal plates and even continents. Findings of the study appeared in the journal Earth and Planetary Science Letters. Researchers, led by Calvin Miller, compared zircon crystals formed during Earth’s first geologic eon called the Hadean, with those formed contemporaneously in Iceland. Scientific community had said in the past that Icelandic crystals were geologic analog for earth Earth.
Hadean was the first geologic eon of our planet, coming before the Archean. It began about 4.5 billion years ago with the formation of Earth and ended about four billion years ago. In 1980s, scientists discovered zircon crystals that were more than four billion years old. It opened the door for exploration of the planet’s earliest crust.
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Hadean Earth was cool enough to support water formation
Geologists used radiometric dating and other analytical techniques to find out the age of these crystals and the environmental conditions in which they were formed, including temperature and presence of water. Zircon analysis revealed that the Hadean Earth was not completely hellish. During some periods, it had established crusts cool enough to support water formation, most likely on the scale of oceans.
Scientists at Vanderbilt University compared the composition of Icelandic zircon to those that were formed over four billion years ago. They also compared Icelandic zircon with zircon from other modern environments. Why Icelandic zircon? Because in Iceland, a large amount of crust are formed from basaltic magma, which is even hotter than the magmas that built our planet’s current continental crust.
Hadean zircon grew from much cooler magmas
Researchers analyzed more than 1,000 Icelandic zircon crystals for their age, isotopic and elemental compositions. And then they studied the literature for comparable analyses of the Hadean zircon crystals as well as analyses of those from other modern environments. They found that Icelandic crystals were distinctive from those formed in other locations on modern Earth.
They also found that Icelandic zircon formed in magmas they were very different from the magmas in which the Hadean zircons were formed. Hadean zircons grew from much cooler magmas than Icelandic zircons. It indicates that the Hadean Earth was much cooler than previously thought.