One of the theories regarding the origin of life is the theory of the prebiotic soup. This theory suggested that the early Earth had a very gaseous atmosphere. This atmosphere was considered to be full of mostly water, methane, hydrogen and ammonia. It was thought that this mixture was often infused with electricity in the form of lightning and this interaction gave birth to the replicating cell and life. This theory was given support in an experiment conducted by Stanley Miller in which high-voltage electric sparks were passed through a flask containing the kind of atmosphere early Earth was thought to have and amino acids and organic molecules were found in the flask. As more and more of these components were formed, they began combining further to create the replicating cell. Although the results of the experiment seemed to explain the creation of life on earth, later studies revealed that the early atmosphere was filled with more carbon dioxide and less hydrogen than the original experiment.
Another theory that has been proposed is the so-called ‘genes first’ theory. This theory was brought forward as scientists attempted to explain how DNA and catalytic proteins could develop on their own and yet work so seamlessly with each other. Basically, the problem is that DNA is required in order to put together the codes to create protein but DNA can’t be formed without the previous existence of a special kind of protein called a catalytic protein. A catalytic protein is a protein that initiates action on its own. But it’s been discovered that RNA can also be catalytic. The theory suggests that a single RNA cell provided the code for new ‘models’ and also proved the catalyst for making these replications. The theory has been tracked backwards to showing that these catalytic RNA molecules are formed spontaneously when RNA nucleotides are activated on a common clay. But there is still the problem of where did the RNA nucleotides come from and no research so far has found the answer. This answer also depends somewhat on the idea of the prebiotic soup, but it was assisted when it was again shown that the early environment had more hydrogen.
Approaching the problem from a completely different angle, there is the metabolism-first approach to how life began on Earth. According to this theory, there was a mineral-based metabolizer ready in the form of pyrite or fool’s gold. This kind of mineral is more formally known as iron disulfide and is a mineral that is found in ancient and modern day enzymes. This rock naturally breaks in smooth surfaces on which this theory suggests carbon dioxide and hydrogen sulfide mixed to create more complex organic compounds. The theory is also supported by the realization that these compounds were very abundant in the early atmosphere and that the energy needed to convert these inorganic compounds into organic ones could have been provided by the hydrothermal vents that are still found in existence along the mid-Atlantic Ridge. Evidence of smaller vents existing in the ocean today give this theory strength because they provided pockets where the necessary compounds would have been brought into closer proximity and at cooler temperatures than today’s ‘black smokers’. The compounds created here are then proposed to have perhaps provided the missing building blocks that would make the RNA model work.
A fourth theory regarding the origin of life on this planet is the extra-terrestrial model. This theory suggests that life on earth was brought here by fast-moving comets crashing into the planet’s surface. There have been studies that showed that comets could carry organic compounds such as amino acids and that there are other places in our solar system that might have had these types of compounds, such as Mars and the moon Europa. Upon arriving on Earth, then, these compounds fell into the existing ‘primordial soup’ and began creating life. This theory is somewhat supported by experiments with tiny worms that have proven capable of surviving the extreme conditions of life on board a fast comet for up to four days. One of the major problems with this theory is discovering just where the original life came from and how it hitched a ride on a comet to make its trip to Earth.
Works Cited
- Robinson, R. “Jump-Starting a Cellular World: Investigating the Origin of Life, from Soup to Networks.” PLoS Biology. Vol. 3, N. 11, (2005). Web.
- Shwartz, Mark. “New field of astrobiology has scientists pondering the extraterrestrial origin of life.” Stanford Online Report. (2000). Web.