It turns out that the earth is about 60 million years older than we thought. While that’s still just a correction to the age of the earth (roughly 4.54 billion years old), it still changes our picture of when the atmosphere started to form and gives scientists a more accurate view of the planet’s early history.
“Xenon gas signals allow us to calculate when the atmosphere was being formed, which was probably at the time the Earth collided with a planet-sized body, leading to the formation of the Moon. Our results mean that both the Earth and the Moon are older than we thought though it’s not possible to give an exact date for the formation of the Earth,” said Dr. Guillaume Avice, a geochemist at the University of Lorraine in Nancy during a talk at the Goldschmidt Geochemistry Conference this week.
Radioactive dating puts a window on the age of the earth
Most estimates for the age of the earth are based on radiometric dating, which analyzes radioactive isotopes found in rocks with incredibly long half-lives (hundreds of millions of year or more). Since the balance of these isotopes is homogenized whenever a rock is melted you can compare old specimens to newer ones to calculate when the older ones must have been formed. You can’t actually pinpoint the age of the earth this way, but you can establish a minimum age. In other words, if you find a rock that radiometric dating tells you is 4 billion years old, then logically the earth must be at least that old.
Setting a maximum age follows the same logic. Since the oldest rocks found in the solar system have been dated at 4.568 billion years old, we can assume the earth is younger than that unless someone can push the age back even further (which is certainly possible).
Avice’s research examines xenon gas instead of rocks
The research done by Avice and his colleagues is a little bit different. At some point in the earth’s history it collided with another planet-sized body, knocking off a huge chunk of mass that eventually became the moon and creating a lot of quartz. Some of that quartz sealed in xenon gas, creating a veritable time capsule that the researchers used to determine that the collision took place about 40 million years after the formation of the solar system. Since the earth’s atmosphere was thought to have formed 100 million years after the solar system, this pushes back the whole timeline by 60 million years.