Chemical Evolution
The formation of organic molecules from inorganic molecules is referred to as chemical evolution. Chemical evolution describes chemical changes that took place on primitive Earth that gave rise to first life forms. Around 4 billion years ago, the Earth’s atmosphere consisted of chemicals such as water vapour, methane, ammonia and hydrogen. Sunlight, heat from volcanoes and lightning caused these molecules to combine in the shallow seas and produce organic molecules such as sugars which later combined to form big molecules such as proteins, RNA and DNA.
Organic Evolution
The enzymes, proteins, RNA and DNA once formed constituted a self-replicating system enclosed in a selectively permeable, protective lipid sphere which further evolved into membrane bound proto cells and finally into living cells. This process is called organic or biological evolution. Organic evolution refers to the slow and gradual process by which living organisms have changed from the simplest unicellular form to the most complex multicellular forms that are existing today. Organic evolution primarily involves modifications in the existing organisms and the inheritance of these modifications.
