Existing explanations on how it formed are unsatisfactory

Mar 29, 2012 11:54 GMT  ·  By

In a paper published in the March 29 issue of the top scientific journal Nature, experts propose that Earth's evolution occurred differently than current theories call for. A large number of cosmic impacts may have altered the way our planet should have evolved by a considerable margin.

As such, this world is very different from the meteorites spinning around it. These objects, called chondrites, were for over a century believed to have roughly the same make-up as our planet.

However, our latest investigations into the matter appear to indicate that – even though Earth and those space rocks coalesced from the protoplanetary disk around the young Sun – they are very different.

Chondrites are fragments that have chipped off the most common types of asteroids in the Inner Asteroid Belt (IAB), which spans between the orbits of Mars and Jupiter. This feature of the solar system also contains a protoplanet called Vesta and a dwarf planet called Ceres.

One of the most common theories on how our planet came to be suggests that Earth was gradually formed from chondritic materials that originated in the Sun's protoplanetary disk. In time, the thinking goes, more and more of these materials came together, and coalesced to form a larger celestial body.

But studies have begun to demonstrate that our world's crust differs in composition from chondrites. These discrepancies can only be accounted for by hidden reservoirs of chemicals that lie within our planet. However, this is not likely to be the case.

One major obstacle to this proposal is the fact mantle plumes exist. These are enormous swells of hot, molten rock that develop in the upper layers of the mantle, and which push on the tectonic plates from underneath. If such reservoirs existed, then they would generate enormous heat.

But mantle plumes carry only a fraction of the heat that should be produced, which means that the proposed reservoirs are most likely not there. “There cannot be a hidden reservoir, which most version of the chondritic hypothesis for the Earth require,” Ian Campbell tells Space.

The expert, who is based at the Australian National University in Canberra, was the lead author of the study. He says that these discrepancies are the reason many scientists are now proposing that numerous space impacts removed these chemical imbalances from our planet, during its early days.

This is a process of “collision erosion,” as some scientists call it. “During collision, this basalt is lost, taking the enriched elements with it. We think all large planetary bodies form by this process,” Campbell explains.

“Their compositions will vary from planet to planet because the nature of the collisions will vary and therefore the amount of enriched outer shell lost will vary from case to case,” he concludes.