Stanley Miller and Harold Urey of the University of Chicago, conducted an experiment in 1952 called the Miller-Urey experiment. The experiment consisted of series of tubes and flasks containing a mixture of water (H20), Methane (CH4), Ammonia (NH3) and Hydrogen (H2). The flask containing the liquid was continuously heated and the evaporated vapor was passed through a chamber which had electrodes to simulate lightning. The vapor was then cooled and fed back into the flask. The experiment tried to simulate the conditions that existed on earth some 4.2 Ga to 3.7 Ga (Ga stands for Gigaannum, 10^9 years i.e. a billion years). After a week of this, it was found that 10-15% of the carbon in the initial mixture was now in the form of organic compounds including 20 common Amino Acids, with Glycine, the smallest amino acid being the most abundant. Amino Acids are the building blocks of proteins.
During the Hadean era (Hell like), the earth atmosphere was devoid of oxygen and consisted with CO2 or Methane as the source of Carbon, water in oceans or as water vapor as source of Hydrogen and atmospheric Nitrogen with phosphates and sulphides added to the mix. The Miller-Urey experiment suggests that the lightning in the atmosphere or the Sol’s ultraviolet radiation could have acted as a catalyst in this mixture and given rise to basic organic compounds needed for life. These compounds then later formed more complex organic compounds like proteins and eventually DNA and life. This theory basically postulates that
a. There was an atmosphere filled with the right chemicals and not filled with the wrong ones (Absence of Oxygen)
b. Right stimulation resulted in simple organic compounds
c. More complex compounds formed
d. Life came into existence.
Though there are evidences that a existed and b happened, how c came about is still not completely answered. Deep sea vent hypothesis says that these reactions happened in underwater volcanic vents. Another hypothesis says that the Iron compounds (in one theory, Zn compounds) may have provided the energy and catalyst required for complex polymer formation. Yet another theory suggests that concentration of Uranium deposits in some places may have helped it (Radioactive Beach hypothesis).
RNA World hypothesis suggests that RNA based life was a precursor to the current DNA based life. It is also suggested that other nucleic acids like Peptide Nucleic Acid (PNA), Threose Nucleic Acid (TNA) or Glycol Nucleic Acid (GNA) may have been formed to be replaced by RNA and later by DNA.
From these pre-pre-pre-historic goo, formed the first “cells”. A million years or may be a couple passed and we saw some of these cells joining to better survive. Life kept going and now we have a man writing about things that happened a mind boggling 4 billion years ago.
* I am neither a microbiologist nor a biochemist.