Researchers have discovered the oldest material on Earth – and it’s much older than the planet itself. Tiny grains isolated from a meteorite that fell in Australia were found to be between 5 and 7 billion years old, meaning they predate the Earth, the Sun and the solar system itself.
In 1969, a fireball was seen exploding in the sky near Murchison, Victoria, Australia. Fragments of the meteorite totaling 100 kg (220 lb) were found across an area of over 13 sq km (5 sq mi). With so much of the strange space rock recovered, the Murchison meteorite has been extensively studied, yielding some fascinating results. Just last year, for example, it was found to contain extraterrestrial sugars essential to life.
And now, researchers have discovered that the Murchison meteorite also contains samples of the oldest material ever found on Earth. About 30 years ago it was found that the rocks housed “presolar grains” – tiny grains of silicon carbide older than the Sun. But their exact age hadn’t been determined until now.
To figure that out, the researchers on the new study measured how long these presolar grains had been exposed to cosmic rays. These high-energy particles flit around space and can pass through solid matter, creating new elements inside the existing minerals as they interact with them. That means the scientists can measure the amount of these new elements in the grains to determine how long they were floating around in space – and, ultimately, how old they are.
In doing so, the team found that most of the grains were between 4.6 and 4.9 billion years old. The Sun itself is at the younger end of that range, at 4.6 billion years old, while the Earth didn’t form until 4.5 billion years ago.
But the oldest of the grains were dated to more than 5.5 billion years, making them the oldest known material on Earth. The team says that the history of these grains could be traced back even further, to the stars that birthed them some 7 billion years ago. According to the researchers, this finding suggests that our galaxy went through a period of intense star formation around that time.
Presolar grains have been discovered in other meteorites before, such as the Hypatia stone and LAP-149, but their ages weren’t able to be pinned down.
The research was published in the journal PNAS.
Source: ETH Zurich
