Earth’s Early Chemical Environment – a Nucleotide Soup
The chemical environment of the early earth was definitely lethal to life as we know it today, but for the first amino acid that formed in that environ it was perfect! It is natural for us to think of life consisting only of the life forms that are familiar to us such as the autotrophs (‘self’ feeders) and heterotrophs (feed on others) alive today. The simple single-celled organisms that were the first forms of life here survived in situations that are lethal to some of their descendants! Think of the extreme organisms, called Archaea, such as the halophiles, acidophiles, and thermophiles. They are examples of life surviving in conditions that would kill most other modern-day living things.
In 1953 two scientists, Miller and Urey, mixed what they thought were the components of Earth’s early atmosphere: methane, ammonia, water, and hydrogen. The mixture was exposed to electric sparks to simulate sunlight energy and lightning. It only took a few days to get an organic ‘soup’ consisting of lactic acid, urea, acetic acid and several amino acids.The major components of amino acids – Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), – include the same atoms used in the original mixture of methane (CH4), ammonia (NH3), water (H2O) and hydrogen (H2).
Adding to this mixture on the earth were numerous comets and asteroids that hit from time to time. These chunks of space rock were filled with organic molecules. (By the way, in 1969, scientists found lipids and the five nitrogenous bases (adenine, guanine, cytosine, thymine, and uracil) in a large meteorite that crashed to earth. The nitrogenous bases are the building blocks of DNA and RNA.)
The first amino acid that came together in the organic soup of the early oceans on earth was not actually alive. It lead to life but was not alive itself. There are some characteristics of life including the ability to reproduce, respond to stimuli, and grow and develop, that the first organic molecule could not do. It was, however, the necessary precursor for living things yet to come. Oparin and Fox have shown that in the absence of oxygen amino acids tend to link together on their own to form short protein chains. These amino acids in the form of protein chains collected in groups to form small round droplets. Some of these droplets were even able to break down glucose. These droplets would be called proto-life because the ability to break down a glucose molecule is one of the necessary functions of many types of living cells.
In the nucleotide soup of Earth’s early oceans the genes (genes are sections of DNA or RNA that are many nucleotide sequences long) of the earliest bacteria coded for proteins that performed the simplest of life’s functions – breaking down glucose – definitely a necessity for a living thing, unless the living thing is an Archaea. The single-celled organisms in kingdom Archaea were once grouped with bacteria but research has shown they are as much different from bacteria as organisms in the other 4 kingdoms. Archaea live in extreme places and have the ability to make their own ‘food’ using hydrogen gas, sulphur, or carbon dioxide. Some researchers have proposed the Archaea haven’t changed much from the first forms of life on Earth. Other researchers propose the Archaea came later, after the first cells that were able to break down glucose for energy. Dr. Carl Woese studied the bacteria to determine evolutionary relationships and determined the Archaea were a group separate from bacteria. Since this information has only been around since the late 1970s, more research needs to be done to determine if the Archaea came before the glucose-using bacteria.
With all these amino acids linking together in the absence of oxygen and with millions and millions of years for different combinations to come together, I think it is likely a gene that is beneficial to life would develop. The chances of life occurring in the situation that was the early Earth were good!
