A vast number of geologists are striving to pinpoint the catalysts behind the origin of life on Earth. While many theories are proposed, their validity is being tested by biologists who are continually designing experiments to verify whether these facts fit with the idea of the evolution of life from nonliving chemicals. Both geologists and astronomers are looking for evidence from Earth, Moon, and other planets to reconstruct the exact conditions prevalent in the early solar system. At the same time chemists and biochemists are evaluating the process of how complex organic molecules could have formed in such environments.
One such hypothesis delves into the probability of extraplanetary factors being the stimulus for the evolution of life on Earth. It postulates that planets have organic compounds delivered to them from space, from comets or meteorites, but it is unlikely that this process by itself leads to the evolution of life. Organic molecules must have been delivered to Mercury, Mars, Venus, and the Moon as well as to Earth but the inhospitable conditions on those planets must have been detrimental to the evolution of life. Experiments show that it is fairly simple to form large quantities of organic compounds in planetary atmospheres and on planetary surfaces, given the right conditions. Space-borne molecules may have added to the supply on a planetary surface, but they would never be the only source of organic molecules that led to the origin of life.
Almost all geological evidence of these early times has been destroyed, especially by the catastrophic impacts around 3.9 Ga (Giga annum): the scenario of a cool watery Earth very early in its history is based on evidence from a few zircon crystals that survived as recycled grains in later rocks. But if there was early life on Earth, it would have been wiped out by the catastrophes at 3.9 Ga. The life forms that were our ancestors could not have evolved and survived until after the last sterilizing impact. However, small late impacts may have encouraged the evolution of life. All comets and a few meteorites carry organic molecules, and comets in particular may have delivered some to Earth. But processes here on Earth also formed organic chemicals. Intense ultraviolet (UV) radiation from the young Sun acted on the atmosphere to form small amounts of very many gases. Most of these dissolved easily in water, and fell out as rain, making Earth’s surface water rich in carbon compounds. The basic organic molecules that make up cell membranes and cell contents may have been present in reasonable amounts in the oceans of early Earth. We must still explain how they evolved into a cell that could reproduce itself.
This is just one of the theories which suggest what factors could have influenced the origin of life on our planet. More and more secrets are revealed on a daily basis and scientist are keeping a track on new possibilities. Only time will tell which of these theories are close to determining the real truth.