Scientists studying what they think is grains of stardust in a meteorite the hit the Earth in 1969 have discovered the oldest material ever found on Earth, material that is actually older than the Earth itself.
The meteorite, dubbed the Murchison meteorite after the nearest city in Australia where it landed, has been a treasure trove of information for planetary scientists because so much of it was recovered right after impact.
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.
Obviously there are uncertainties with this result, though their age estimates are quite reasonable and largely robust.