As regards the origin of life on earth, we used to believe that when life began on earth, the atmosphere contained nitrogen, hydrogen and other gases but no oxygen. Consequently, the sun's rays prevented life from developing on land. That explained why the first living organisms developed only under the sea. Under the influence of photosynthesis, the oxygen in the atmosphere increased and life expanded. Complex living organisms developed. As the oxygen in the atmosphere increased, life, which depends on the equilibrium of the atmosphere, was possible on the surface of the earth.
Recently, we have come up with a very different hypothesis. We believe that hundreds of millions of years ago, a meteor crashed into a then-lifeless planet. Embedded in the meteor were carbon compounds that were to become the seeds of all life on earth. Our current hypothesis is that there was a seeding from elsewhere. Let's say a meteor that had originated in Mars landed in the Antarctic, and it contained evidence of life.
Last month, we observed the Leonid meteor showers, which occur in every November when Earth passes through the debris shed by the comet Tempel-Tuttle. We were aboard two U.S. Air Force craft that flew at night from the United Kingdom to Israel, then back through the Azores to Florida. The path allowed us to observe the meteors - some no bigger than a grain of sand - from an altitude of 11-and-a-half kilometers. Images of the meteors were fed through infrared spectrographic-instruments that can detect the unique chemical fingerprints of complex organic molecules of the type that may have"seeded" life on earth. Our spectrographic instruments caught a meteor "in the act" of disseminating organic molecules.
We have a list of perhaps 100 carbon-containing compounds that have been identified. These are the building blocks of life. We use the term "pre-biotic life" to describe them. So that is a major interest of astrobiology - to search for the chemicals that exist in the universe outside of earth that could lead to life, probably in some sort of continuous process. |