Meteorites Rich in Amino Acids
2 Apr, 2008 11:44 am
The origins of life on Earth have not yet been clearly established. It is thought that the first living systems may have made use of organic materials from its surroundings. Immediately prior to the origin of life on Earth the planet's surface was bombarded with organic matter from space, seeding the planet with organic compounds thought to be required for the origin of life.
Amino acids are the building blocks of proteins, which participate in many of the chemical reactions inside living cells. Amino acids could have been formed on the early Earth, but they have also been found in some ancient meteorites.
The two meteorite samples analyzed by the research team were collected in Antarctica in the 1990s and held in the meteorite collection at the NASA Johnson Space Center in Houston (Texas). These meteorites belong to a rare type called CR chondrites, which is thought to be one of the oldest and best preserved extraterrestrial samples we have access to. They are fragments of asteroids formed shortly after the birth of our solar system.
The meteorite named EET92032, GRA95529, have concentrations ranging between 180 and 249 parts per million, which is at least 10 times higher than levels previously measured in other meteorites. Throughout the cosmos, carbon can be found in heavy and light forms and the proportions can be measured using sophisticated instruments. Because organic molecules from extraterrestrial sources use a heavy form of carbon while life on Earth uses the light variety, Martins and colleagues were able to rule out contamination as a factor in their result.
The meteoritic amino acids probably formed in an asteroid before it broke up. For example, amino acid chemical precursors from the solar nebula, or even from the interstellar medium, could have been combined with water in the asteroidal parent body to make the amino acids.
Therefore, by studying these and other primitive CRs, the scientists can have a better idea of the origin of the amino acid. After the parent body of the meteorite broke up, some of the fragments could have crashed to Earth and the other terrestrial planets. About 3.8 to 4.5 billion years ago, meteorites are thought to have delivered extraterrestrial organic molecules to the Earth, just before life emerged on our planet.
The flux of organic matter delivered during this period of time is thought to have been extremely high (in the order of tons of carbon per year). The new results show that meteorites delivered a very high abundance of organic molecules important in terrestrial biochemistry to the early Earth, therefore being available for emergent life systems. It is not known what the production rates of key molecules in primitive extraterrestrial materials, the more likely it is that exogenous material played a role in the origin of life.
"Our results suggest that exogenous delivery may have indeed played a more important role in the origin of life on Earth than previously thought," states Zita Martins.
While considering the role of meteoritic amino acids in the origin of life, Matins is encouraged by the new findings. She believes that "our increasing understanding of the materials available for the first life in the solar system suggests that we are all products of cosmic chemistry. The history of life on Earth may have begun in the stars."
1. Z. Martins et al. "Indigenous amino acids in primitive CR meteorites", Meteoritics and Planetary Science.