Origin and Evolution of Life in the Oceans Abiogenesis- study of how life on earth could have arisen from inanimate matter (Spontaneous Generation) Life seems to have started in the oceans long ago Fossil evidence supports the theory that life began in the oceans The 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 atmosphere Alexander Oparin suggested that organic compounds could have undergone a series of reactions leading to more complex molecules John 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 theory Their experiment produced 25 amino acids and other organic compounds But it did not produce life

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

Oxygen and evolution The 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 appeared Autotrophs began breaking down carbon dioxide into oxygen. This raised the atmosphere’s 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 years Natural selection – organisms with favorable characteristics are more likely than those with less favorable characteristics to survive and reproduce Sometimes new characteristics appear in an organism due to mutation of the DNA The 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 organisms The first multicellular organisms lived in the ocean. Over time, evolutionary processes allowed organisms to adapt to life on land