The Earth and moon are around 60 million years older than previously measured, based on new research.
Most geologists and astrophysicists believe the moon was created when the young Earth was struck by a body the size of Mars, called Theia. This impact is believed to have kicked up material from our home world, sending it into orbit. There, it formed a ring around the Earth for a short while, before coalescing to form the moon.
A team of geochemists from the University of Lorraine in Nancy, France have discovered evidence of the impact in isotopes of gas. They claim this shows the impact occurred roughly 40 million years after the formation of the solar system. That would make the Earth, and our lunar attendant, roughly 60 million years older than previously believed.
One of the challenges for geologists studying ancient rocks is the lack of clues that the scientists usually use to measure dates. In younger rocks, layers are formed in striations over each other, providing an important dating mechanism for researchers. However, these layers had not yet formed when the earliest rocks were created. One method of determining the age of these rocks is by studying concentrations of isotopes of gases trapped in their structure. Isotopes are different versions of elements, possessing the same number of protons, but a differing number of neutrons.
Xenon gas trapped in quartz found in South Africa and Australia between 3.4 and 2.7 billion years ago was analyzed. There are nine stable isotopes of this elemental gas. The levels of various isotopes were compared to levels today. This provided a window into the past, allowing the team to determine the age of the atmosphere.
Any air on the ancient Earth would have been blown away from the impact which created the moon. Most geologists dated formation of the atmosphere to around 1000 million years after the creation of the solar system. This new work suggests the primitive air first encircled our planet 60 million years earlier than that, pushing back the date for the formation of the moon.
"This might seem a small difference, but it is important. These differences set time boundaries on how the planets evolved, especially through the major collisions in deep time which shaped the solar system," Bernard Marty, one of the researchers on the project, said.
Although it is impossible (so far) to pinpoint exactly how long ago our planet was formed, this new research pushes back the age a little more. The oldest rocks in the solar system have been measured to be 4.568 billion years old, so the Earth cannot be older than that figure.
