/Dust grains found in meteorite are older than the sun and Earth | CBC News

Dust grains found in meteorite are older than the sun and Earth | CBC News

A scanning electron micrograph shows a silicon carbide grain, about 8 micrometres in its longest dimension, from a meteorite that crashed into Australia in 1969. The image was released in Chicago on Monday. (Janaina N. Avila via REUTERS)

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 say.

The oldest of 40 tiny dust grains trapped inside the meteorite fragments retrieved around the town of Murchison in Victoria state dated from about seven billion years ago, about 2.5 billion years before the sun, Earth and rest of our solar system formed, the researchers said.

In fact, all of the dust specks analyzed in the research came from before the solar system’s formation — thus known as presolar grains — with 60 per cent of them between 4.6 and 4.9 billion years old, and the oldest 10 per cent dating to more than 5.6 billion years ago.

The stardust represented time capsules dating to before the solar system. The age distribution of the dust — many of the grains were concentrated at particular time intervals — provided clues about the rate of star formation in the Milky Way galaxy, the researchers said, hinting at bursts of stellar births rather than a constant rate.

“I find this extremely exciting,” said Philipp Heck, an associate curator at the Field Museum in Chicago who led the research published in the scientific journal Proceedings of the National Academy of Sciences.

“Despite having worked on the Murchison meteorite and presolar grains for almost 20 years, I still am fascinated that we can study the history of our galaxy with a rock,” Heck added.

The grains are small, measuring from 2 to 30 micrometres in size. A micrometre is a one-thousandth of a millimetre, or about 0.000039 of an inch.

Blown by stellar winds

Stardust forms in the material ejected from stars and carried by stellar winds, getting blown into interstellar space. During the solar system’s birth, this dust was incorporated into everything that formed, including the planets and the sun, but survived intact until now only in asteroids and comets.

The researchers detected the tiny grains inside the meteorite by crushing fragments of the rock and then segregating the component parts in a paste they described as smelling like rotten peanut butter.

Dust-rich outflows of evolved stars similar to the pictured Egg Nebula are plausible sources of the large presolar silicon carbide grains found in meteorites like Murchison. ( ESA/Hubble and NASA. Inset courtesy of Janaína N. Ávila)

Scientists have developed a method to determine stardust’s age. Dust grains floating through space get bombarded by high-energy particles called cosmic rays. These rays break down atoms in the grain into fragments, such as carbon into helium.

These fragments accumulate over time and their production rate is rather constant. The longer the exposure time to cosmic rays, the more fragments accumulate. The researchers counted these fragments in the laboratory, enabling them to calculate the stardust’s age.

Scientists previously had found a presolar grain in the Murchison meteorite that was about 5.5 billion years old, until now the oldest-known solid material on Earth. 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.

This is a large chunk of the Murchison meteorite from the Field Museum of Natural History meteorite collection in Chicago. The meteorite is a carbonaceous chondrite. (James St. John/Wikimedia Commons, licenced under CC BY 2.0)

Original Source