Rocks from Early Earth

How did Earth form? Newly-discovered clues may help answer that longstanding question.

Volcanic rocks collected from Baffin Island in the Canadian Arctic show signatures of ancient chemicals dating back to just a few tens of millions of years after Earth formed.  The study was published this week in the journal Nature.

It’s not just in a couple rocks, either. According to National Geographic,

Even better, the newly analyzed rocks—which reached the surface some 62 million years ago—suggest a whole reservoir of the primordial rock could still lie somewhere beneath the Arctic, the study says.

How did the rocks reach the surface? New Scientist says:

The rocks were thrown up by volcanoes in the Arctic wastes of Baffin Island and Greenland only 62 million years ago, but it seems they came from a store of rock in the mantle that formed 4.5 billion years ago – just after Earth formed.

A supporting article in Nature describes the importance of this evidence:

[Earth’s] primordial building blocks of iron-rich metal, oxides, silicate minerals, and volatile elements and compounds have been transformed over geological time into the modern-day structure of core, mantle, crust, ocean and atmosphere.

“This was a key phase in the evolution of the Earth,” says co-author Richard Carlson of the Carnegie Institution's Department of Terrestrial Magnetism. “It set the stage for everything that came after.”

Because the Earth “recycles its building blocks so thoroughly” (National Geographic) through “billions of years of melting and geological churning” (ScienceDaily) by “forces that shook and scrambled our planet” (80beats, Discover), these primordial rocks generally do not exist. In fact, as National Geographic states, “Why the reservoir survived remains a mystery.”

But the fact that it did survive excites geologists. From New Scientist:

If the dates are right… these rocks were undisturbed for almost all of Earth's history, and so hold chemical clues to our planet's origin. It is widely thought that Earth was assembled from material similar to that found in meteorites called chondrites. But Baffin's ancient rocks are different: they contain less of certain heavy elements than chondrites do.

What happened to these elements could be the next clue in this ancient mystery…

Want more information about the Earth’s formation? Stay tuned for the Academy’s next planetarium show, Life: A Cosmic Story. Opening November 6th, the film will take audiences through Earth’s history and describe the geological evidence for the origin of life.

Creative Commons image by Angsar Walker