快猫短视频

A thin layer of 3.3 billion-year-old rock contains unexpected treasure: organic matter that was carried to Earth by meteorites when the planet was still young.

The find supports the idea that organic, meaning carbon-based, chemicals from space supplied some of the raw materials for the first life on Earth. It could also complicate the search for life on other planets.

鈥淭his is the very first time that we have found actual evidence for extraterrestrial carbon in terrestrial rocks,鈥� says Frances Westall of the CNRS Centre for Molecular Biophysics in Orle虂ans, France.

快猫短视频s have long known that carbon-based chemicals can be found in space. In particular, molecules like amino acids and nucleotides that are used by life have been found in meteorites. As a result, many suspect meteorites carried these essential building blocks of life to the primeval Earth.

Westall and her colleagues studied a slab of rock from the Josefsdal Chert in eastern South Africa, which contained many layers laid down over time.

鈥淭here was this one layer with this outstanding signature,鈥� says Westall. 鈥淚t鈥檚 very similar to organic matter in meteorites.鈥� Further analyses revealed that the layer contained minerals called spinels that are known to form in meteorite impacts.

The team suspects the carbon-based matter was thrown into the air as a fine dust after the meteorite hit. The dust then fell to earth and was buried under volcanic ash. This preserved the extraterrestrial carbon in one discrete layer: in other circumstances it would have mixed with living matter, rendering it undetectable. Similar samples may be rare, Westall says, but not impossible to find.

Meteorites hit the Earth regularly from its birth 4.5 billion years ago until about 3 billion years ago. 鈥淭he organic matter from the carbon-rich meteorites must have been raining down at quite a high rate,鈥� says Westall. The carbon could have been used by the first life. We do not know when life formed, but there are fossil microbes from 3.4-3.5 billion years ago.

Layers of meteoritic carbon may exist on other planets, says Westall. That will complicate our efforts to find evidence of life, extinct or otherwise, on worlds like Mars 鈥� Westall is involved in the forthcoming ExoMars 2020 mission.

鈥淲e鈥檝e got to be prepared to find a mixed signature of extraterrestrial carbon mixed in with traces of biogenic carbon,鈥� she says. 鈥淭hat adds an extra level of difficulty.鈥�