Life's building blocks more common than thought

Posted by Kate Taylor

An analysis of meteorite samples has revealed that there's more than one way of building amino acids in space, raising the odds of life elsewhere.

The NASA researchers say that the discovery lends support to the theory that life on Earth could have been kicked off by a 'kit' of ready-made parts created in space and delivered to Earth by impacts from meteorites and comets.

In the past, amino acids have been found in carbon-rich meteorites with mineralogy that revealed the amino acids were created by a relatively low-temperature process involving water, aldehyde and ketone compounds, ammonia, and cyanide called 'Strecker-cyanohydrin synthesis'.

But when the scientists analyzed samples from fourteen carbon-rich meteorites with minerals that indicated they had experienced high temperatures – in some cases, over 2,000 degrees Fahrenheit - they found amino acids there too.

"Although we've found amino acids in carbon-rich meteorites before, we weren't expecting to find them in these specific groups, since the high temperatures they experienced tend to destroy amino acids," says Dr Aaron Burton, a researcher in NASA's Postdoctoral Program stationed at NASA Goddard.

"However, the kind of amino acids we discovered in these meteorites indicates that they were produced by a different, high-temperature process as their parent asteroids gradually cooled down."

The team hypothesizes that the amino acids were made by a high-temperature process involving gas containing hydrogen, carbon monoxide, and nitrogen called Fischer-Tropsch-type (FTT) reactions. They occur at temperatures ranging from about 200 to 1,000 degrees Fahrenheit with minerals that facilitate the reaction.

These same reactions are used to make synthetic lubricating oil and other hydrocarbons, and during World War II, were used to make gasoline from coal.

Researchers believe the parent asteroids of these meteorites were heated to high temperatures by collisions or the decay of radioactive elements. As the asteroid cooled, FTT reactions could have taken place on mineral surfaces, using gas trapped inside small pores in the asteroid.

FTT reactions could even have created amino acids on dust grains in the solar nebula, the cloud of gas and dust that collapsed under its gravity to form the solar system.

"Water, which is two hydrogen atoms bound to an oxygen atom, in liquid form is considered a critical ingredient for life," says Burton.

"However, with FTT reactions, all that's needed is hydrogen, carbon monoxide, and nitrogen as gases, which are all very common in space. With FTT reactions, you can begin making some prebiotic components of life very early, before you have asteroids or planets with liquid water."

The team believes the majority of the amino acids they found in the 14 meteorites were truly created in space, and not the result of contamination from terrestrial life - for several reasons.

First, the amino acids in life are frequently linked together in long chains, either as proteins or as polymers - and these weren't. In addition, the most abundant amino acids found in biology are those found in proteins, but these were rare in the meteorites.

Finally, ice taken from underneath one of the meteorites had only trace levels of amino acids, suggesting the meteorites are relatively pristine.

The team now wants to expand its search for amino acids to all known groups of carbon-rich meteorites.