The Nature Geoscience journal published findings yesterday after scientists discovered a piece of Earth’s crust dating 4.4 billion years old. The breakthrough zircon gem was found in the Jack Hills of Western Australia in 2001.
Zicrons are an essential part of the Earth’s crust known to be found in igneous, metamorphic and sedimentary rocks. Usually less than one millimeter in size, finding large zircons is rare. The sample found by Wisconsin scientists is the oldest recorded find.
The implications of the confirmed zircon age were so significant researchers anxiously waited on two separate age-determining tests. The first used was a highly popular test which determines radioactive decay of uranium to lead within a sample. While this would be generally accepted, some scientists believe this technique can be flawed, as possible movement of lead inside crystals can distort the dating.
The second test used, called the “atom-probe,” identifies lead atoms and their respective mass. This additional testing proved the gem, a tiny piece of Earth’s crust, was indeed 4.4 billion years old. As soon as the integrity of the chemical record inside the zircon was established, publication of the findings was initiated. This new evidence completely alters the way the science community approaches Earth’s early history.
The age of the solar system, for example, is only 4.56 billion years old itself. This means the Earth, at most, could have only taken 160 million years to develop a crust. Since the Earth was a molten rock 4.5 billion years ago, this new evidence suggests the planet cooled much quicker than previously thought.
John Valley, geosciences professor and author of the study, said if Earth cooled this quickly life could have formed much earlier than believed. The stage of Earth’s history was aptly named after the Greek Underworld God, Hadean for its assumed high temperatures, and hell like landscape.
But it seems soon after the Hadean eon, Earth may have been cool enough to maintain oceans and support life. Valley and his team of scientists from the University of Wisconsin-Madison focused on pinpointing the moment Earth became habitable for life. He said the study supports the idea of a “cool early earth.”
The oldest archaic form of bacteria are dated at 3.4 billion years ago. However, based on the aging evidence found in the zircon could have existed 4.3 billion years ago. “We have no evidence …life existed then,” said Valley. However, he argues, according to this new information, there is no reason life could not have started formation 4.3 billion years ago.
The present information tells us the continental crust of the planet began forming 4.4 billion years ago. Future studies will continue to search for evidence of life, which now has a broader timeline, according to Valley. Scientists are likely to continue research in close proximity to Western Australia because tectonic plates are constantly damaging rocks. The site may be the only place on the planet with this sort of rock preserved.
In science, a little goes a long way. The historic gem is the size of two human hairs, only 200 by 400 microns. This tiny piece of 4.4 billion year old history has changed the way scientists understand the Earth’s crust.
By Erin P. Friar