There are currently several theories on how life appeared on Earth.
1. Biopoiesis
a. Electricity
According to this theory, the energy required for life to appear may have been provided by lightning. It was shown in 1953 that, in an atmosphere rich in water, methane, ammonia and hydrogen, amino acids and sugars can be generated by electric sparks. As the early atmosphere of Earth contained little hydrogen, volcanic clouds may have provided the necessary conditions. A long time period such as millions of years could have given birth to larger and more complex molecules.
b. Deep-sea vents.
This theory places the first origins of life near submarine hydrothermal vents. These provide hydrogen-rich molecules that could have been concentrated together through the action of mineral catalysts from the surrounding rocks.
2. Panspermia.
This theory does not provide a definitive answer on how life appeared. Instead, it proposes that the first life was brought to earth by meteorites from Mars or comets from other star systems.
3&4 RNA & Chilly start
The theory that has most support describes an RNA World in which the first molecules that enabled life were RNA. As DNA, RNA can store information and catalyze chemical reactions.
It is thought that RNA could have developed in an icy environment on Earth. It has been discovered that freezing actually speeds up certain key activities of RNA. Thus, the Chilly start theory was proposed in which life started in an icy environment.
5. Clay Theory
Alexander Graham Cairns-Smith was the scientist who proposed that the first molecules of life met on clay. This material may not only have concentrated these organic compounds, but also organized them into patterns. This effect would be similar to that of our genes. After a period of time, the tangled amino patterns would change into amino acids that in turn will give rise to proteins.
6. Simple Beginnings
As an alternative to the origin of life from complex molecules such as RNA, cyclical interactions between smaller molecules could hold the answer. These could have been surrounded by structures similar to cell membranes, Over times, these molecules increased in complexity and efficiency.
