Washington, Sep 16 :
Conditions on the Earth for the first 500 million years after its formation may have been surprisingly similar to present day conditions – complete with oceans, continents and active crustal plates, report geologists.
To reach this conclusion, scientists compared zircon crystals that were formed more than four billion years ago with those formed in Iceland which has been proposed as a possible geological analogue for an early Earth.
“We reasoned that the only concrete evidence for what the Hadean was like came from the only known survivors: zircon crystals. No one had investigated Icelandic zircon to compare their telltale compositions to those that are more than four billion years old or with zircon from other modern environments,” said Calvin Miller, the William R. Kenan junior professor of earth and environmental sciences at the Tennessee-based Vanderbilt University.
The Hadean is the first geologic eon of the Earth and lies before the Archean. It began with the formation of the Earth about 4.5 billion years ago and ended some 4,000 million years ago.
The team analysed about 1,000 zircon crystals for their age as well as elemental and isotopic compositions.
They then searched the literature for all comparable analyses of Hadean zircon and for representative analyses of zircon from other modern environments.
The team discovered that Icelandic zircons are quite distinctive from crystals formed in other locations on modern Earth.
“We also found that they formed in magmas that are remarkably different from those in which the Hadean zircons grew,” added Tamara Carley, a doctoral student at Vanderbilt.
Most importantly, the analysis found that Icelandic zircons grew from much hotter magmas than 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,” researchers concluded.
The study was published online in the journal Earth and Planetary Science Letters.