Nearly Seven-Billion-Year-Old "Real Stardust" Found, Say Scientists

Egg Nebula are plausible sources of the large presolar silicon carbide grains found in meteorites like Murchison. and R. Sahai. Inset SiC grain with

The Oldest Known Material on Earth Is Officially Older Than The Solar System

A team of researchers from the USA and Switzerland analysed 40 pre-solar grains contained in a portion of the Murchison meteorite, that fell in Australia in 1969.

"They're solid samples of stars, real stardust", said Philipp Heck, the lead author of a study on the particles and a curator at the Field Museum in Chicago, which acquired the largest pieces of the Murchison meteorite.

Heck notes that there are lifetimes' worth of questions left to answer about presolar grains and the early Solar System.

About 30 years ago it was found that the rocks housed "presolar grains" - tiny grains of silicon carbide older than the Sun.

And one of the grains analyzed in a study published today in the Proceedings of the National Academy of Sciences is estimated to be roughly 7 billion years old, making it the oldest known material on Earth.

This period of star formation would have been about 7 billion years ago, according to the team's findings. The sun formed about 4.6 billion years ago, and Earth formed about 4.54 billion years ago.

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.

A meteorite that crashed into rural southeastern Australia in a fireball in 1969 contained the oldest material ever found on Earth, stardust that predated the formation of our solar system by billions of years, scientists said on January 13.

For the study, Heck and his colleagues examined 40 of these so-called boulders from Murchison, grinding up bits of the meteorite and adding acid, which dissolved minerals and silicates and revealed the acid-resistant presolar grains.

Researchers compared the process to burning down a haystack to find the needle. The new study is evidence of the latter.

While the space granola floated through the cosmos, it was bombarded with cosmic rays. These rays are high-energy particles that travel through our galaxy and penetrate solid matter.

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". "Most of them, they just fly through the solid grain. But rarely there is an interaction, [and] one of those protons can hit an atom in the grain". Lifetimes of interstellar dust from cosmic ray exposure ages of presolar silicon carbide. "The silicon can be split into helium and neon", Heck says.

The unusual concentration of grains of about the same age suggests a "baby boom" of stars, Heck said. The concentration of certain isotopes provides an estimation of how long ago the rock was zapped by the rays. "It only works if the rainfall is constant over time, and that's luckily the case with cosmic rays".

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.

The paste of ground-up meteorite released a stench "like rotten peanut butter", study co-author Jennika Greer, a graduate student at the Field Museum and the University of Chicago, said in a statement.

"Some of these cosmic rays interact with the matter and form new elements", Dr Heck said. "It's not a straightforward way of measuring isotopic abundance and getting an age directly from that measurement". They're between 5 billion and 7 billion years old.

Stars are born when dust and gas floating through space find each other, collapse in on each other and heat up. A fallen grain, as part of our galactic history, is the closest thing to a sample return from a star.

"And then it took about two to two-and-a-half billion years for those stars to become dust producing", Heck explained.

And, Heck said, the discovery of a furious starburst in microscopic grains wrapped up in a meteorite confirms that star formation ebbs and flows.

While it's actually not unheard of for meteorites to contain grains of material that predate the Solar System - they're called "presolar grains" - they are rare, and hard to identify because the bits of material are so small, and deeply embedded in the rock. With more grains, researchers can refine their age estimates to further test the accuracy of the method. After inserting the samples into a mass spectrometer, the researchers could study the concentrations of different isotopes.

"It's so exciting to look at the history of our galaxy".

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