Scientists do not have a definite answer to that but they do know that Earth’s atmosphere in the ancient times was extremely different from the present time. After conduction of various experiments, scientists have deduced the fact that the Earth’s atmosphere has changed over time to accumulate life.
THE EARLY EXPERIMENTS
Stanley Miller along with Harold C. Urey conducted an experiment in 1952 for understanding the formation of complex organic molecules under the conditions present in early Earth. They held the belief that methane, hydrogen, ammonia and water vapour made up Earth’s early atmosphere. In their experiment, they contained all these gases in an airtight container and then passed electric sparks in the gases for stimulating lightning. This process continued for a week.
The end result was the coating of a reddish brown substance on the walls of the container. This substance consisted 11 vital amino acids out of 20 that are used by life on Earth. Various scientists have verified the said experiment over the times. Some scientists hold the belief that carbon dioxide, water vapour and nitrogen formed the Earth’s early atmosphere.
THEORIES REGARDING THE ORIGIN OF LIFE
There are various theories regarding the origin of life. Some of them are:
- Life began with an electric spark or lightning that generated amino acids. Miller-Urey experiment in 1953 provided the evidence for this theory.
- Life began with RNA in a series of reactions. This theory believes that RNA was contained in simple capsules that evolved into more complex molecules. Metabolism occurred which led to origin of life on Earth.
THE LAST UNIVERSAL COMMON ANCESTOR
Biochemists and astrobiologists believe that each and every life form on Earth has evolved from a common ancestor that was present in ancient times. They conduct search operations that try to find traits common to all the life forms. They believe that all these common traits have been inherited from LUCA (Last Universal Common Ancestor).
As for LUCA, the available information is that she used all the same 20 amino acids that is use presently in our proteins. She used DNA for storage of genetic information, used RNA and consisted of hundreds of proteins performing various functions. LUCA is believed to be the ancestor for Archaea, Bacteria and Eukaryotes kingdoms. She is believed to have lived more than 2 billion years before. Sunlight and water provided for much needed evolutionary growth.