The Murchison meteorite is a meteorite that fell in Australia in 1969 near Murchison, Victoria. It is part of the carbonaceous chondrite class, a group of meteorites that contain many organic compounds. Because of its large size (more than 100 kilograms or about 220 pounds) and the fact that scientists observed its fall, the Murchison meteorite is one of the most studied meteorites in the world.
In January 2020, scientists reported that the oldest material found on Earth to date are silicon carbide particles from the Murchison meteorite. These particles are 7 billion years old, which is about 2.5 billion years older than the 4.54-billion-year age of Earth and the Solar System. The study noted that estimates of how long dust lasts are based on models that focus on small dust grains. These models rely on assumptions that have large uncertainties.
History
On 28 September 1969 at approximately 10:58 a.m. local time, near Murchison, Victoria, in Australia, a bright fireball was seen splitting into three pieces before disappearing, leaving a cloud of smoke. About 30 seconds later, a shaking was heard. Fragments were found spread out over an area more than 13 kilometers (5.0 miles; 3,200 acres), with each piece weighing up to 7 kilograms (15.4 pounds). One piece, weighing 680 grams (1.5 pounds), broke through a roof and landed in hay. The total mass of the collected meteorite is more than 100 kilograms (220 pounds).
Classification and composition
The meteorite is part of the CM group, which is a type of carbon-rich meteorite. Murchison, like many other CM chondrites, is classified as petrologic type 2. This means that water-rich fluids changed its structure on its parent body before it fell to Earth. CM chondrites, along with the CI group, contain a lot of carbon and are among the oldest and most chemically simple meteorites. Murchison has many calcium and aluminum-rich parts. Studies of this meteorite have found more than 15 amino acids, which are important building blocks of life.
In January 2020, scientists discovered that silicon carbide grains in the Murchison meteorite are made of material that formed before our solar system existed. The oldest of these grains is about 3 billion years older, with some uncertainty, than Earth and the solar system, which are 4.54 billion years old. This makes the grains the oldest material found on Earth so far.
Organic compounds
The Murchison meteorite contains common amino acids such as glycine, alanine, and glutamic acid, as well as less common ones like isovaline and pseudoleucine. A complex mix of alkanes was also found, similar to results from the Miller–Urey experiment. Serine and threonine, which are often considered to come from Earth, were not found in the samples. A group of amino acids called diamino acids was also identified in the meteorite.
In 1970, scientists reported that the amino acids in the meteorite were racemic, meaning they had equal amounts of left-handed and right-handed forms. This suggested they formed in a non-living way, as Earth’s proteins usually have only left-handed amino acids. In 1982, it was found that alanine had more left-handed forms, but because alanine is a protein amino acid, some scientists thought this might be due to Earth contamination. However, in 1997, left-handed excesses were also found in non-protein amino acids, which suggested the asymmetry might have an extraterrestrial origin. Some amino acids were racemic, with equal left- and right-handed forms. Around that time, scientists also found an increase in nitrogen isotopes, but these results were later questioned due to possible errors in analysis.
By 2001, scientists had identified more organic materials in the meteorite, including polyols. The meteorite contained both left-handed and right-handed amino acids. Most amino acids used by living organisms are left-handed, while most sugars used by life are right-handed. In 2005, Swedish chemists showed that left-handed amino acids like proline might have helped create the uniform handedness seen in life.
Studies show that the inside of well-preserved Murchison fragments is largely unchanged. In 2010, scientists used advanced tools like spectroscopy to find 14,000 molecular compounds, including 70 amino acids, in a sample. The analysis might have missed many more compounds, with scientists estimating there could be millions of organic compounds in the meteorite.
In November 2019, the Murchison meteorite, along with the Northwest Africa 801 meteorite, was the first to show evidence of pentoses, including ribose, in space using gas chromatography–mass spectrometry. Straight-chain five-carbon aldoses were found, but other types like tetroses, sugar alcohols, sugar acids, and deoxyribose were not.
In 2020, NASA reported that hexamethylenetetramine was found in the Murchison, Murray, and Tagish Lake meteorites. Scientists also found purine and pyrimidine compounds in the Murchison meteorite. The carbon isotope ratios for uracil and xanthine were measured as +44.5 ‰ and +37.7 ‰, respectively, which suggest these compounds did not come from Earth. This discovery shows that many organic compounds could have been delivered to Earth by early Solar System objects and might have played a role in the origin of life.