1 Impacts on comets can create building blocks of life, too on Sun Dec 01, 2013 11:24 pm
No one knows how life on Earth began. But for it to happen, some simple chemical building blocks would have been needed. Many scientists argue that the Earth’s violent past, with its massive volcanoes and regular meteor impacts, played a role in making these building blocks.
But some of the simple molecules that could have served as building blocks are found on comets, too. Mark Price, a space scientist at the University of Kent, suspected that these icy bodies could be involved in making these chemicals.
The modern era of origins-of-life research began 60 years ago at the University of Chicago. In 1953, chemists Stanley Miller and Harold Urey simulated a lightning strike in the atmosphere of the early Earth. They found that passing a spark through a mixture of methane, ammonia, hydrogen, and water made small amounts of amino acids. Amino acids are among the fundamental building blocks of life and are assumed to be necessary for life to begin.
In 1963, two chemists from the Space Science Laboratory in California suggested that meteorite impacts on Earth could also provide enough energy to make amino acids. This process, called shock synthesis, occurs when chemicals react at the incredibly high temperatures and pressures created during a collision.
The famous astronomer Carl Sagan experimented with shock synthesis by bursting hot pressurized tubes containing gases that resembled the early Earth’s atmosphere. His process also created amino acids in surprisingly large amounts.
Price’s idea, reported in Nature Geoscience, was not too different from Sagan’s. But creating a comet impact in a lab is not easy. Price used a gun to fire tiny bullets at 7,150 meters per second, more than 20 times the speed of sound, at blocks of ice. To model a comet, these ice blocks were made of methanol, ammonia, and carbon dioxide. Right after the bullet hit the ice block, heat was used to evaporate chemicals that did not react, leaving behind what Price hoped would be amino acids.
And indeed they were. Analysis revealed them to be glycine, alanine, and four other amino acids that are not used by life on Earth. Glycine made up most of the mixture.
The range of amino acids produced can be used to work out how they would have been formed. Because they had fewer carbon atoms than most amino acids, Price thinks they were made through a similar process as the Miller-Urey experiment. The impact of the pellet creates intense pressure, up to 500,000 times higher than atmospheric pressure. In these conditions, oxygen can add to methanol to create the carbonyl compounds needed to make amino acids.
If comet impacts can make amino acids too, these results add to the growing body of evidence that some of life’s building blocks may have been abundant in the Solar System before life began. But the steps involved in using them to make life still remain a matter of hot debate.[You must be registered and logged in to see this image.]]