Scientists identify oldest material on Earth in meteorite

Scientists identify oldest material on Earth in meteorite

Scientists identify oldest material on Earth in meteorite

Scientists crushed fragments from the meteorite down into a powder, forming a paste that was then dissolved in acid and studied. "And when we know how many cosmic ray-produced helium and neon atoms we have, we can calculate an age, because the production rate is pretty constant over time". They are from silicon carbide, the first mineral formed when a star cools.

The Murchison meteorite was discovered on September 28, 1969 in Murchison, about 160 kilometres north of Melbourne.

Most presolar grains measure about 1 micron in length, or are even smaller. But they offer astronomers insight into how stars formed in the early stages of our galaxy.

A new study of the presolar grains of the Murchison meteorite recovered in Australia was published Monday in the Proceedings of the journal National Academy of Sciences.

"We've used this really old sample, the oldest solid samples available to science, to try to learn something about the history of our galaxy", said Philipp Heck, a meteorite expert at the Field Museum of Natural History in Chicago.

As for the oldest grain, Haenecour says, "I think it is hard to really actually know that this grain is 7 billion years old", but adds that it does appear to be much older than the other grains in the study.

"This is one of the most exciting studies I've worked on", says Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and lead author of a paper describing the findings in PNAS. These grains were originally separated from Murchison meteorite fragments at the University of Chicago over 30 years ago, but they were preserved so future scientists could study them with modern dating technologies.

The oldest of the dust grains were formed in stars that roared to life long before our Solar System was born.

"Each grain probably came from a different star", Dr Heck said.

Once the presolar grains were isolated, the researchers figured out from what types of stars they came and how old they were by measuring their exposure to cosmic rays.

And, Heck said, the discovery of a furious starburst in microscopic grains wrapped up in a meteorite confirms that star formation ebbs and flows. This grain is about 8 micrometers in size.

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"We have more young beans than we expected", said Heck.

By counting all the fragments produced by the cosmic rays, and knowing how often they are produced, scientists can work out how old the stardust is.

"We have some grains which are a billion years older than the Sun, making them 5.5 billion years old ... a few grains that are 2 billion years older and we have one grain that is 3 billion years older [than the Sun]". These miniscule particles date back once again to the full time our solar power system nevertheless needed to emerge (which took place 4.6 billion years back).

Stardust from half the lifetime of the universe ago fell to Earth in a meterorite 50 years ago, and is believed to be the oldest solid material ever found.

The researchers learned that some of the presolar grains in their sample were the oldest ever discovered on Earth.

Previously, the oldest pre-solar grain dated with neon isotopes was around 5.5 billion years old.

Stardust grains were dragged into the Murchison meteorite as it traveled through space in its eventual collision course with Earth. "Once all the pieces are segregated, it's a kind of paste, and it has a pungent characteristic-it smells like rotten peanut butter".

Researchers compared the process to burning down a haystack to find the needle.

Tens of thousands of presolar grains were extracted from the Murchison meteorite, but only 40 were large enough to be dated, he added. "Our hypothesis is that most of those beans ... were formed in an episode of enhanced star formation".

It provided new evidence to a debate about whether new stars form at a steady rate, or whether there are highs and lows in the number of new stars over time.

"Large" is a relative term in this case, considering that the entire mass of material analyzed in the new study is just 300 nanograms, or 300 billionths of a gram. "But thanks to these grains, we now have direct evidence of an improved star formation period in our galaxy seven billion years ago with meteorite samples". "There was a time before the start of the Solar System when more stars formed than normal".

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