The Infant Earth: Less Hellish But Still Probably Not a Fun Place
Recent comparisons between the oldest rocks on the earth and more modern ones bolster the theory that the infant earth was not as hellish as we we once thought it was.
Depictions of earth when it was a baby less than 500 million years old often show it to be a red-hot planet with magma oceans pock-marked with the incessant eruptions of volcanoes. This time frame is often called the Hadean which is the very first geologic interval of the earth (generally characterized as a time before rock solidified into remnants we could find today). The technical term for this time frame is called an Eon and the Hadean is only one among 4 that earth’s history has been divided into by geologists, paleontologists, and other aficionados of our planets geologic history. Eons are subdivided into smaller units of time called Eras, followed by Periods, then Epochs and finally Ages. You’ve probably heard of the Jurassic and Cretaceous. These are Periods in the Mesozoic Era which is part of the Phanerozoic Eon. In case you’re wondering, Eons are sometimes grouped under the one all-encompassing umbrella term SuperEon. Speaking of sometimes, the Hadean Eon itself is often not even considered an official Eon unto itself presumably because we know so little about it.
One thing that we think we know about the Hadean is that is was hot and nasty. So much so that the name Hadean is derived from Hades, the ancient Greek God of the Hellish underworld. Hell isn’t what it used to be it seems though since parts of the Hadean Eon appears to have been similar in some ways to our modern Age with oceans and continents. In fact, some rocks formed in recent ages were created in a hotter environment than those from the Hadean, over 4 billion years ago.
This notion that the Hadean wasn’t quite what we thought gained prominence in the 1980s but recently received a boost by a team of geologists led by Calvin Miller, Professor of Earth and Environmental Sciences at Vanderbilt University. Their study describes the first detailed comparison between Zircon crystals (minerals found in granite) forged during that ancient time with more modern ones.
These comparisons looked at the oxygen signatures in the crystals which, according to the study abstract…:
“Hadean zircons and almost all Icelandic zircons grew from magmas with substantial contributions from materials that had interacted with surface waters. In the Hadean case, the interaction occurred at low temperatures, while in Iceland, it was a high-temperature interaction”
The conclusion then is that not only did the ancient zircons grow in an environment similar to modern ones, they grew in an environment that was both colder and wetter than those being formed today.
This is not to say that the Hadean would make a pleasant vacation time for you, your significant other, and your time machine. During this Eon gargantuan asteroid impacts were still occasionally happening which made the Dinosaur impact look like a pleasant fireworks display. They were, though, infrequent enough at times to allow many millions of years to pass relatively unmolested permitting at least parts of the earth to appear surprisingly non-Hades like.
Image Credit: Don Dixon, cosmographica.com