Origin and Evolution of Life in the Oceans

Origin and Evolution of Life in the OceansAbiogenesis- study of how life on earth could have arisen from inanimate matter (Spontaneous Generation)Life seems to have started in the oceans long agoFossil evidence supports the theory that life began in the oceansThe oldest fossils are those of cyanobacteria, dated 3.5 billion years ago

Theories on how life originated:Scientists proposed that the first molecular building blocks of life could have originated from lightning or ultraviolet light in the atmosphereAlexander Oparin suggested that organic compounds could have undergone a series of reactions leading to more complex moleculesJohn Haldane proposed that the primordial sea served as a vast chemical laboratory powere by solar energy. The atmosphere was oxygen free, and the combination of carbon dioxide, ammonia and ultraviolet radiation gave rise to organic compounds

Theories on how life originated:Stanley Miller and Harold Urey tested this theoryTheir experiment produced 25 amino acids and other organic compoundsBut it did not produce life

Theories of how life originatedScientists question this theory because UV radiation would have destroyed these forming moleculesScientists now theorize that life started in the deep ocean, possibly near hydrothermal vents

Oxygen and evolutionThe first organisms were very simple. They probably thrived by breaking down simple compounds in the primordial soup to supply their energy (heterotrophs)As life became more advanced, about 3-3.5 billion years ago, the first autotrophs appearedAutotrophs began breaking down carbon dioxide into oxygen. This raised the atmospheres oxygen content from 1% to the present 21%Oxygen is important to life because oxygen reactions allow organisms to use chemical energy more effectively

The theory of evolution says that over long periods, natural selection and mutation caused the development of all the different life forms and their characteristics. Organisms became more varied and complex over millions of yearsNatural selection organisms with favorable characteristics are more likely than those with less favorable characteristics to survive and reproduceSometimes new characteristics appear in an organism due to mutation of the DNAThe prevailing view in evolution is that changes come in spurts due to significant changes in the environment- Punctuated Equilibrium

It is argued that single- celled organisms then evolved from independent existence to life in colonies. Over millions of years, these colonies evolved into complex multicellular organismsThe first multicellular organisms lived in the ocean. Over time, evolutionary processes allowed organisms to adapt to life on land