Molecules containing large chains of carbon and hydrogen, which happen to be the building blocks of all life on Earth, have been found in meteorites from Mars but scientists have been unsure how this organic carbon was formed and even disagreed on whether or not it came from Mars. 

A new paper shows evidence that this carbon did originate on Mars - but don't call the folks at SETI just yet, it isn't biological. 

Theories about
the origin of the large carbon macromolecules detected in Martian meteorites include contamination from Earth or other meteorites, the results of chemical reactions on Mars, or, more speculative, that they are the remnants of ancient Martian biological life.  The researxh group examined samples from 11 Martian meteorites whose ages span about 4.2 billion years of Martian history. They detected large carbon compounds in 10 of them. The molecules were found inside of grains of crystallized minerals. 

Using an array of techniques, the results published in Science Express were able to show that at least some of the macromolecules of carbon were indigenous to the meteorites themselves and not contamination from Earth. Next the team looked at the carbon molecules in relation to other minerals in the meteorites to see what kinds of chemical processing these samples endured before arriving on Earth. The crystalline grains encasing the carbon compounds provided a window into how the carbon molecules were created. Their findings indicate that the carbon was created during volcanism on Mars and show that Mars has been doing organic chemistry for most of its history. 

"These findings show that the storage of reduced carbon molecules on Mars occurred throughout the planet's history and might have been similar to processes that occurred on the ancient Earth," said
Andrew Steele of the Carnegie Institution. "Understanding the genesis of these non-biological, carbon-containing macromolecules on Mars is crucial for developing future missions to detect evidence of life on our neighboring planet." 

In a separate paper
published in American Mineralogist, the team studied a meteorite called Allan Hills 84001 that was reported to contain relicts of ancient biological life on Mars. The paper demonstrated that these supposed remnants could have been created by chemical reactions involving the graphite form of carbon, rather than biological processes. Both of these papers reveal a pool of reduced carbon on Mars and will help scientist involved in future Mars missions distinguish these non-biologically formed molecules from potential life.