Chapter 22
Self-Quiz
Unit 4: Evolution
The Evolutionary History of Life
Review
Life first evolved in the
between 4 and 3.5
billion years ago
when Earth had very low levels of atmospheric oxygen. Over time, the activity of photosynthetic
in the
period
released oxygen
into the atmosphere and set the stage for the emergence of
, and eventually for multicellular organisms.
The
explosion
marked a period of rapid growth in biological diversity including
green algae.
Most of the modern animal phyla and other groups now extinct appeared at this time, including the
first
.
Descendants of
multicellular
were the
first
to colonize the land during the
period.
During the
period,
fish
began to diversify, and invertebrate animals such as
millipedes
invaded land.
During the
period
plants
such as ferns diversified on land, and the first chordates to
colonize land
were
which probably evolved from
lobe-finned fish.
During the
period
reptiles
appeared and
plants
dominated land with innovations such as the
for
waterproofing,
and
for efficient
transport and support
in early
Gymnosperms.
During the
period
reptiles
flourished due to the success of the
egg
which later led to the development of other
animals. The
supercontinent
formed.
During the
period
and early
appeared.
During the
period
dinosaurs
diversified, and
birds
and
appeared.
Pangea
began to break
up.
During the
period
Angiosperms
diversified, and
became extinct at the
end of this period.
Mammals
started to dominate the terrestrial landscape during the
period, and
humans
started to evolve during the
period.
At least
five
have occurred over the history of the Earth, with a sixth
extinction possibly under way.
The rapid diversification of a group of organisms is known as
, which often occurs after mass extinction events. During the history of life, the
has
increased with time.
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Feb 21, 2006
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