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The Tertiary Period
Overview:
The Tertiary Period began 65 million years ago and lasted more than 63 million
years, until 1.8 million years ago. During the Tertiary Period there were many
changes in climate and in the types of species around the world. One of the most
important facts about this period is that with nearly all of the dinosaurs gone, there
was plenty of room on Earth for the mammals and birds to have lots of babies, and
soon there were all different kinds of mammals and birds all over the Earth. The
Tertiary Period ended with the planet’s last great Ice Age.
Earth Environments:
Plate tectonics were very active during the
Tertiary Period. Some continents ran into each
other: about 60 million years ago California ran
into North America, causing the Rocky
Mountains. About 55 million years ago India
crashed into Asia and made the Himalaya
mountains, and about 30 million years ago Africa
crashed into Europe and pushed the Alps up into
mountains. All of this movement began to
arrange the continents into the way we see them
now.
The beginning of the Tertiary Period was very
warm and moist compared to today’s climate.
Much of the earth was tropical or sub-tropical.
Palm trees grew as far north as Greenland! As
plate tectonics made the continents drift apart,
it caused a lot of volcanoes. The carbon
dioxide released by these volcanoes cooled
down the Earth gradually throughout the
Tertiary period. This cooling trend continued
and by the end of the Tertiary Period, an ice age had begun. The mountains of the
world were covered by glaciers (including the newly formed Himalayas and Alps).
The huge amounts of water locked up in the ice lowered the level of the sea and
land bridges appeared. This enabled migrations of both plants and animals across
these land bridges. The Tertiary period, which had begun hot and humid, ended in a
cold dry ice age.
Life Forms:
The extinction event
at the close of the
Cretaceous Period
wiped out the
dinosaurs, large
reptiles, and many
other species. This
left room for new
animals to take over.
The mammals
became the dominant
animals. Most of the
main groups of
mammals were present during the Tertiary Period. With the dinosaurs and other
large reptiles gone mammals grew in size, numbers and diversity. They found
homes and made a living in the sea, on land, and in the air.
Birds did almost as well as mammals during the Tertiary Period. Many of the birds
we know today were present. There were also
many large flightless birds that are now extinct.
These birds did particularly well before the
mammals developed so many species.
Probably the most important thing to occur
during the Tertiary period happened around
six million years ago. Fossil evidence shows
that at that time the first people evolved out of
the early primates in Africa. By 2.5 million
years ago, these people were using stone
tools and entering what we call the Paleolithic
period of human history.
The Precambrian Era
Overview:
The Precambrian is the name which describes the large span of time in Earth's
history. It spans from the formation of Earth around 4600 million years ago to about
542 million years ago. The Precambrian accounts for 88% of geologic time.
Very little is known about the Precambrian, despite it making up a large part of the
Earth's history. The Precambrian fossil record is poor. This is because many
Precambrian rocks have undergone heavy pressure and temperature turning them
into metamorphic rocks. This process makes it difficult to determine where they
came from. Many of the rocks from the Precambrian era have either been destroyed
by erosion, or remain deeply buried in the earth’s crust.
Earth Environments:
Details of tectonic plate motions are not well known in the
Precambrian. It is generally believed that small continents
existed prior to 3000 Ma, and that most of the Earth's
landmasses collected into a single supercontinent around
1000 Ma. The supercontinent, known as Rodinia, broke up
around 600 Ma.
A number of ice ages have been
identified going as far back as 2200 Ma,
in which the entire globe was covered in
snow and ice. The Earth might have
looked something like the image below, in
which there were cold conditions all the
way to the equator, resulting in something
scientists call "Snowball Earth".
The atmosphere of the early Earth is poorly known, but it is thought to have very little
oxygen. When evolving life forms developed photosynthesis, oxygen began to be
produced in large quantities, causing an ecological crisis sometimes called the
oxygen catastrophe. The oxygen was immediately tied up in chemical reactions,
primarily with iron. Scientists know this because older rocks contain massive
banded iron formations that were apparently laid down as iron and oxygen first
combined.
Life Forms:
It is not known when life originated. Well-preserved bacteria older than 3.46 billion
years have been found in Western Australia. Possible fossils 100 million years older
have been found in the same area.
A diverse collection of soft-bodied forms (like
jellyfish) were found from a variety of locations
worldwide between 542 and 600 Ma.
Hard-shelled creatures appeared
toward the end of that timespan.
The oldest fossil evidence of
complex life is found at least 580
million years ago.
The Permian Period
Overview:
The Permian Period is the final period of the
Paleozoic Era. It began about 290 million years
ago and lasted until 248 million years ago. The
greatest mass extinction that has ever occurred
on earth took place at the end of this 42-million-
year period. There are many theories about the cause of the Permian extinction, but
many scientists hypothesize it could ha ve been caused by huge amounts of volcanic
activity. We know from recent volcano eruptions that large eruptions can cause the
temperature to drop all around the world.
The Permian Period gets its name from a region of west-central Russia called Perm
Oblast. This is where rocks from this time were first found. Even though it was first
found in Russia, this layer of rock can be found across the world.
Earth Environments:
For most of the Permian, life on Earth was
much like it had been in the Carboniferous.
Temperatures were cooler because the
continent of Pangea was moving northward.
Mountains were forming as the supercontinent
Pangea moved. When the continent of Siberia
collided into the northern part of Euramerica,
Pangea was complete. The Ural Mountains
were pushed up by this collision.
Pangea was shaped like a large “C.” It
surrounded the Tethys Sea. The rest of the
Earth was covered by a huge ocean named
Panthalassa. Even though the ocean covered
much of the earth, Pangea was so large that the interior did not benefit from the
ocean waters. Deserts were places in the center of Pangea where the temperatures
changed from very cold to very hot. In some places there was rarely or never any
rain. Over all the earth was dry during the Permian Period.
Life Forms:
The dry climate was bad for water-loving plants and animals like ferns and frogs, but
good for dry land plants and animals, so there got to be a lot more of them. The first
reptiles were already living on land, but during the Permian period there got to be
many more reptiles, and more different kinds of reptiles.
Pelycosaurs evolved from their
beginnings in the Carboniferous.
These animals look like a reptile,
but have skull characteristics that
are similar to mammals. The most
famous of the pelycosaurs is the
Dimetrodo n. Like many other
pelycosaurs, fossils show that
Dimetrodon had a large sail on its back. The sail could have been used to help keep
the body temperature stable in the dry Permian environment.
New plants developed that were adapted to the
dryer conditions. These plants had seeds. One
of the earliest of these plants still exists today. It
is called the Ginkgo. Most of the trees living
during the Permian period were conifers.
Conifers are trees with seeds in cones, like
Pine Trees. Just like with animals
paleontologists find fossils of these types of
trees in layers of rock from the Permian Period.
During the Permian Period, these plants and animals spread across the land. It was
easy for these trees and reptiles to spread all over because the land was all joined
together in one big continent. Similar fossils from this period can be found all across
the continents today.
The Cretaceous Period
Overview:
The Cretaceous Period covered the time span of 144 million years ago to 65 million
years ago. There was a minor mass extinction at the end of the Jurassic Period
that is the sign of the beginning of the Cretaceous. Many of the species of bivalved
mollusks (similar to clams) became extinct at this time.
There seems to have been a serious event that
caused the major mass extinction at the end of
the Cretaceous Period. It is called the KT event for
(K)Cretaceous and (T) Tertiary, the first period of
the Cenozoic Era which follows. A popular theory is
that a meteor hit the earth in the Gulf of Mexico.
This caused many geologic activities. Volcanoes
erupted, clouds, smoke, and dust covered the skies
keeping the sun’s light away from the planet for
years. This would have caused huge changes in the
climate and vegetation, and it is likely responsible
for the extinction of the dinosaurs as well as many
other types of life.
Earth Environments:
During the Cretaceous Period continents drifted away from each other, as the
continents separated, the climate got cooler and rainier, and there was even snow in
some places and glaciers on high mountains. But by the middle of the Cretaceous
period, the movements of the tectonic plates caused a lot of huge volcanic eruptions
all over the planet, and these volcanoes shot large amounts of carbon dioxide into
the air. The greenhouse effect of all this
carbon dioxide caused a global climate
change that warmed up the planet again.
Many of these volcanic eruptions happened
underwater in th e area that is now our
Atlantic Ocean. These volcanoes created
underwater mountains that grew as the
Atlantic Ocean got wider. As these
mountains grew they moved so much water
that the oceans were about 100 meters
higher than today! This caused many inland
seas to form. In North America, an inland
sea divided the continent across the plains
of modern-day Canada, imagine a sea going
through the middle of North America!
Life Forms:
The fossil record shows that animal life continued
to develop during the Cretaceous Period and new
species of dinosaurs became important. The
ceratopsian dinosaurs appeared for the first
time. These were plant-eating dinosaurs and the
most famous example is the triceratops. It had
three horns and a huge, bony frill that formed its
skull. But probably the most famous dinosaur of all
lived during the Cretaceous Period, and it wasn’t a
plant eater! The Tyrannosaurus ruled the land at
the end of the Cretaceous Period. Tyrannosaurus
was a large theropod dinosaur. Like all
theropods it walked on two legs and was carnivorous.
Although not as successful as the dinosaurs fossils show
small mammals existed during the Cretaceous Period, but
they were not very important. These were tiny creatures
compared with the giant dinosaurs. Unlike the dinosaurs that
laid eggs, these mammals developed their offspring inside their bodies. Birds were
another important type of animal to develop and become more common at this time.
Mammals and birds would become very important after the KT extinction event
wiped out the dinosaurs at the end of the Cretaceous Period.
Probably the most important development for life had nothing to do with animals
though! The most important development of the Cretaceous Period was the growth
of flowering plants. Before this, most of the trees had been plants with cones. Now
trees began to produce flowers. The ancestors of many modern tree species
appeared during the Cretaceous including the magnolia and the maple.
The Carboniferous Period
Overview:
About 359 million years ago, the Carboniferous period got started and lasted until
about 290 million years ago. It lasted for about 64 million years. The name
“Carboniferous” came from the large amounts of carbon-bearing coal that was
formed during the period.
Environmental Conditions:
When these ferns died, they formed
thick
layers of dead plants that eventually
turned
into coal. Most of the coal in the
world
today comes from ferns that grew
during
the Carboniferous period. So much
carbon
got used up making coal that there
wasn't
enough to combine with oxygen to
make
carbon dioxide, and instead the
oxygen
atoms had to just make oxygen
molecules. Because of that, oxygen levels in the atmosphere rose much higher than
before (and higher than they are now).
Plate tectonics caused the Euramerica
continent to smash into Godwanaland, pushing
the land up to make the Appalachian
Mountains that run along the Atlantic coast of
North America. Asia also ran into the other side of Europe to make the Ural
Mountains. These are some of the oldest mountains that are still around today.
These mountains had no plants covering them. During rainy seasons huge amounts
of surface rock was washed into flood plains and deltas.
The end of the Carboniferous period is marked by global climate changes due to the
glaciers that covered the South Pole. The mass extinctions that mark the end of
other geologic periods were not present, yet many species did go extinct during this
time. The marine environments were most affected by these climate changes, so the
extinctions were mostly invertebrates that spent their lives in the seas.
Life Forms:
Although insects like spiders had already
land for many millions of years, now some of
fly like flies or dragonflies. Animals with
were just beginning to get started on land.
animals, amphibians like frogs, had to go
ocean to lay their eggs. The frogs evolved to
because that was the only kind of land animal
this time.
been living on
them began to
backbones
These earliest
back to the
eat
insects,
there was at
But by about 310 million years ago, the climate was changing. It was getting much
drier and hotter on land. So the plants and animals evolved to take advantage of
that. Some early pine trees developed the ability to make seeds, so they could
make baby pine trees even where there wasn't any water for their spores. And, in
the same way, some of the amphibians developed into reptiles with the ability to lay
eggs with hard calcium shells, so they could lay eggs on land in dry places and
didn't need to stay near the water anymore.
Insects also grew well in the humid and high-oxygen conditions. One of the largest
was the Meganeura. This large ancestor of the dragonfly had a wingspan of 60 to 75
cm. Another large arthropod lived on the floor of the Carboniferous forests. The
Arthropleura was a giant millipede that could grow to more than one and a half
meters long. They sometimes had as many as 30 pairs of legs!
The Cambrian Period:
An Explosion of Life
Overview:
The Cambrian Period marks the beginning of the Paleozoic Era. It immediately
follows the Precambrian Era. The period lasted for nearly 53 million years, from
about 543 million years ago until 490 million years ago. The Cambrian Period began
with an explosion of life forms. It ended in a mass extinction.
Environmental Conditions:
The climate at the beginning of this period was cold, but over time the climate in all
parts of the Earth grew warmer. There were no glaciers at the North or South Pole.
This made the seas a good place for
many
species to live. The continents were
still
forming. They were mostly barren
rocks. The
land had no plant or animal life on it
yet.
Earth's land was broken up into
smaller
continents, but they were drifting
closer
together, and about 500 million years
ago plate
tectonics brought all of the land on Earth together to make a new supercontinent
called Pannotia.
Towards the end of the period, advancing glaciers would have lowered the
temperature of the shallow seas where so many species lived. Changes in the
temperature and the amount of oxygen in the water would have meant the end for
any species that could not adapt.
Life Forms:
During the Cambrian Period there was an explosion of life forms. Most of these were
in the water. Many animals with no backbones lived in the shallow seas. These
animals were invertebrates.
One species was so plentiful and had such
numbers and so many species that it is
called the ruling species of the period. This
called a trilobite. The trilobite was an
with a tough outer skin. It got its name from
lobes in the hard skin. The trilobite was also
first animals to have eyesight. During the
there were more than 100 types of trilobites.
great
sometimes
species is
arthropod
the three
one of the
Cambrian
There were plenty of other species living during the Cambrian Period also. Mollusks,
worms, sponges and echinoderms filled the Cambrian seas. Sponges grew in
Cambrian seas, too. There was even an early type of early fish living during the
Cambrian Period. It was the Pikaia. Pikaia looked a bit like a worm with a long fin on
each side of its body. The nerve cord was visible as a ridge starting behind the head
area and extending almost to the tip of the body.
One of the most fearsome hunters in the
seas was the Anomalocaris. This animal
exoskeleton like an arthropod, but it did not
jointed legs that would make it a true
This large animal fed on trilobites and other
worms and mollusks.
Cambrian
had an
have the
arthropod.
arthropods,
Many of the creatures living in the Cambrian seas developed hard structures for
defense, hard shells, scales, and spikes covering the outside of the body.
The plants of the Cambrian were mostly simple, one-celled
algae. The single cells often grew together to form large
colonies. The colonies looked like one large plant.