Earth Scientists Don Baker and Kassandra Sofonio at McGill University have published a new theory of earth crust’s formation with a novel twist.
Their resulting paper, published in the journal Earth and Planetary Science Letters, posits a new theory of “aerial metasomatism” — a term coined by Sofonio to describe the process by which silica minerals condensed and fell back to earth over about a million years, producing some of the earliest rock specimens known today.
Conventional theory holds that all of the early Earth’s crustal ingredients were formed by volcanic activity.
Scientists believe that a Mars-sized planetoid plowed into the proto-Earth around 4.5 billion years ago, melting the Earth and turning it into an ocean of magma. In the wake of that impact — which also created enough debris to form the moon — the Earth’s surface gradually cooled until it was more or less solid. Baker’s new theory, like the conventional one, is based on that premise.
The atmosphere following that collision, however, consisted of high-temperature steam that dissolved rocks on the Earth’s immediate surface — much like how sugar is dissolved in coffee. This is where the new wrinkle comes in. These dissolved minerals rose to the upper atmosphere and cooled off, and then these silicate materials that were dissolved at the surface would start to separate out and fall back to Earth in what we call a silicate rain.
To test this theory, they spent months developing a series of laboratory experiments designed to mimic the steamy conditions on early Earth. A mixture of bulk silicate earth materials and water was melted in air at 1,550 degrees Celsius, then ground to a powder.
Small amounts of the powder, along with water, were then enclosed in gold palladium capsules, placed in a pressure vessel and heated to about 727 degrees Celsius and 100 times Earth’s surface pressure to simulate conditions in the Earth’s atmosphere about 1 million years after the moon-forming impact.
After each experiment, samples were rapidly quenched and the material that had been dissolved in the high temperature steam analyzed.