Science

7b years: Scientists say oldest solid material found

7b years: Scientists say oldest solid material found”

(100 kilograms) rock that fell on September 28, 1969, near Murchison, Victoria, in Australia. Dairy farmers collected the fragments and sold kilograms of the meteorite to museums and universities.

Why is the Murchison meteorite so special? Now, a new study has identified the oldest known solid material on the planet that precedes the formation of the Solar System.

The oldest of the dust grains were formed in stars that roared to life long before our Solar System was born. The oldest-known minerals that formed on Earth are found in rock from Australia's Jack Hills that formed 4.4 billion years ago, 100 million years after the planet formed.

Funding: NASA, the TAWANI Foundation, National Science Foundation, Department of Energy, Swiss National Science Foundation, Brazilian National Council for Scientific and Technological Development, Field Museum. Those are only 4.4 billion years old.

Scientists from the Field Museum of Natural History in Chicago discovered presolar grains in their sample from the Murchison meteorite and said that it was the oldest ever discovered. They're rare, found only in about five percent of meteorites that have fallen to Earth, and they're tiny-a hundred of the biggest ones would fit on the period at the end of this sentence. The new study is evidence of the latter.

When the dust is in space, it is exposed to cosmic rays that slowly change its composition.

Once the presolar grains were isolated, the researchers figured out from what types of stars they came and how old they were. Volatile organic compounds in rocky meteorites that are abiotic - not formed by living organisms - produce these distinctive smells when they are heated or dissolved, Heck said. Many of them had tales to tell about the meteorite's distinctive aroma. These rays break up atoms in the grain into fragments, like carbon in helium.

"Some of these cosmic rays interact with the matter and form new elements".

The ages of these grains of stardust isn't only important in themselves, but also because of what they tell us about the evolution of our galaxy. The grain is about 8 micrometers on its longest dimension.

Previously, the oldest pre-solar grain dated with neon isotopes was around 5.5 billion years old. Back then, the tools scientists used to analyse these grains weren't as advanced as they are now, so Heck and his team chose to submit the grains to the full gamut of tests.

However, other dating techniques, such as comparing the isotope ratios left behind by decaying radioactive materials, can not yet be used to provide an absolute date for these ancient dust grains. "It's not a straightforward way of measuring isotopic abundance and getting an age directly from that measurement".

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.

Dr Heck told BBC News: "Only 10 percent of the grains are older than 5.5 billion years, 60 percent of the grains are "young" (at) 4.6 to 4.9 billion years old, and the rest are in between the oldest and youngest ones".

Our sun is about 4.6 billion years old, which means that this star dust existed long before our sun or our solar system was even a reality.

Star dust forms in the material that is emitted by stars and carried by star winds and blown into interstellar space. Billions of years later, a chunk of that asteroid crashed into Australia. With more grains, researchers can refine their age estimates to further test the accuracy of the method. The researchers used a particular form (isotope) of the element neon - Ne-21 - to date the grains.

"With this study we are just starting this journey of exploring the history of the galaxy with meteorites", Heck says.



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