Key Takeaways – How Old Is Earth?
- Earth formed around 4.54 billion years ago. Knowing how old Earth is can be more difficult to confirm because Earth's age is not only based on the age of rocks, but also the isotopic estimates of what the source materials of the rock must have been.
- We used to think that by dating a meteorite, we could date Earth because these were the building blocks of our planet. And while that gets us close, we’ve also learned that the early solar system wasn’t quite so cut and dry.
- A practical age to start from for scientists is when the Earth was hit with an object the size of Mars called Theia that then formed the Moon. From here we can surmise when Earth left its beginnings and became a more modern planet. Recent modeling suggests that the formation of the Moon must predate 4.35 billion years.
The Earth has been through the ringer. A six-mile wide asteroid that killed off three-quarters of all species hit the planet 66 million years ago. Four other mass extinction events have taken place on Earth, including the End-Permian event — also called the Great Dying — that happened 252 million years ago.
This was the largest mass extinction event ever and caused 96 percent of all marine species and 70 percent of all terrestrial species to go extinct. This event was the result of volcanic eruptions in Siberia, which led to a massive change in climate. But in all those catastrophes, the Earth has never been completely destroyed. Rather, it took a hit and came back swinging.
But when you ask how old the planet really is, you need to be a little more specific, says John A. Tarduno, a professor of Earth and Environmental Sciences at the University of Rochester in Rochester, New York. Tarduno says that there’s an assumption that the Earth didn’t exist and then all of the sudden, it did — basically, that our planet popped out of nowhere. And that just isn’t the case.
“Earth probably started as a large planetary embryo and then grew larger through collisions,” says Tarduno. This means that the dust and gas particles that resulted from the collisions in the early solar system stuck together and formed larger bodies.
How Old Is Earth According to Scientists?
A practical age to start from for scientists like Tarduno is when the Earth was hit with an object the size of Mars called Theia that then formed the Moon. From here we can surmise when Earth left its beginnings and became a more modern planet. Recent modeling suggests that the formation of the Moon must predate 4.35 billion years.
Experts dated rocks that are assumed to have crystallized from a lunar magma ocean formed after the collision to date this modeling. After the moon formed, the Earth would have been magma that eventually started to cool and became the planet that we know today.
Read More: Massive and Oldest Known Impact Crater Redefines How Life Started on Earth
How Do We Know How Old the Earth Is?
Researchers consistently say that the Earth would have formed around 4.54 billion years ago. These numbers are more difficult to confirm because they’re based not only on the age of the rocks, but also the isotopic estimates of what the source materials of the rock must have been.
“It’s sort of an indirect age so there are uncertainties that leave room for discussion,” says Tarduno.
He adds that there’s quite a bit of evidence to show that the early Earth, sometimes referred to as the “Proto-Earth,” formed later than other planets in the solar system like Mars. Proto-Earth defines the early Earth before its giant impact with the Moon, when it was molten and rotated much more rapidly with a different atmosphere than we would recognize today.
We used to think that by dating a meteorite, we could date Earth because these were the building blocks of our planet. And while that gets us close, we’ve also learned that the early solar system wasn’t quite so cut and dry.
We need to understand the evolution of these building blocks and the stage of the planet that eventually would become Earth. This is much more difficult than just aging a few rocks and figuring out when they fell into place, according to Tarduno.
“The early solar system was a much more violent place than that,” says Tarduno. “Collisions were really common and they were part of the building process.”
Read More: The Speed of Earth’s Rotation Is 1,000 Miles Per Hour – Here’s Why We Don’t Feel a Thing
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