Transcript Origin and Evolution of Life in the Oceans

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