|How did Ocean life form, and why did they evolve?|
This is an interesting question with unclear
answers. There are many theories about how life
began and how it evolved.
One theory is that lightning in Earth's
early, hostile atmosphere provided sparks that
allowed the chemicals found in early oceans and
atmosphere to react and form the building blocks
of life (amino acids for proteins, sugars and
nucleic acids for RNA, DNA, etc.). The idea here
is that these compounds amalgamated into units
that would undergo replication, cross-over
(sharing information), and mutation, and
eventually constituted single-celled organisms
that took in sunlight, used chemicals from the
surroundings, and released by-products that slowly
changed the atmosphere of the Earth.
These ideas are consistent with
"metabolism-first" models -- the idea that
life began with small molecules that underwent
cycles of reactions that became encapsulated in
cell-like units over time. An opposing view is the
idea that the first forms of life began as RNA
("RNA world hypothesis") and then eventually
proteins and DNA developed from RNA.
There are other theories that suggest life may
have formed in the deep sea vents of the
oceans, which are rich with chemical and
thermal energy, or that organic molecules may have
been arranged in patterns in clay. There are also
theories that life began in space on asteroids and
that through successive collisions with the early
Earth, it was introduced to the planet.
For the origin of life, we really don't know.
There are several possible ways it could have
happened, but all involve complex chemistry in an
environment without oxygen using bubbles of
soap-like hydrocarbons containing other chemicals
like RNA. There may have been crystals of certain
types of clay involved, too.
Life can evolve for several reasons. There are
three main reasons: the first is mutation,
where errors or changes happen in the DNA code
that life uses to store information. This is the
source of all differences between living things,
and is required in order for the other types of
evolution to happen. The second is natural
selection, where some existing mutations are
better at surviving or reproducing than others.
Third, there is genetic drift, where some
existing mutations survive due purely to chance.
Generally, natural selection is responsible
for the creation of new species with complex
adaptations: unlike genetic drift and mutation,
natural selection exists because of the laws of
physics, which are nonrandom, and so can act
in a single direction. Drift and mutation are
random, and so have a harder time making anything
complicated and useful.
When the earth was formed, it is thought that
there were only non-living chemicals present, and
no life. However, the gas atmosphere surrounding
the planet and the presence of water on the
surface provided the conditions necessary for the
first life to begin. There are many
theories for how the first life appeared, and
scientists do not agree on any one explanation.
One possibility is that life originated at
volcanic vents under water, where the high
temperatures could provide the energy needed for
chemical reactions that could form the first
primitive life. Scientists have replicated these
high energy conditions in lab to show that such
reactions could occur.
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