Transcript Historical Geology and the history of the continents

The History of the Earth
The evolution of the continents
The evolution of the continents
We have a good idea of the history of the continents over the past
600 million years.
Based on:
Paleomagnetic studies: positions of continents with respect to the
poles.
Geological studies: similarities and differences of rocks on different
continents and interpretations of ancient depositional environments.
Paleontological studies: similarities and differences of fossil
organisms on different continents.
Plate tectonics was ongoing through all of this time, bringing
continents together to form mountain belts and tearing them apart
to form ocean basins.
Over all this time there were other changes taking place:
Variation in O2 levels in
the atmosphere.
Variation in global temperature.
Variation in sea
level on several scales.
Several continental reconstructions are used in the lecture slides but
are not available here. These slides are available at:
"Plate tectonic maps and Continental drift animations by
C. R. Scotese,PALEOMAP Project (www.scotese.com)"
Cambrian Period
Gondwanaland: a
supercontinent made up of
South America, Africa,
Australia, Antarctica, India
and portions of other
continents.
Located near the south pole.
Extensive glaciers covered
much of Gondwanaland.
Part of Nova Scotia was
Attached to Gondwanaland.
North America, Europe, Siberia and Asia were all separate.
The equator passed
through North America
but it was a barren land
mass (no land plants yet).
Sea level rose and fell
and much of the time
North America was an
extensive subaerial
lowland surrounded by
a shallow marine shelf
setting.
Ordovician Period
The separate continents
were beginning to collide
due to plate movement.
North America and
Europe were coming
together
Northern Appalachians
began to form due to
compressive force with
plate convergence.
A trench along the
northwestern margin of
North America formed a
volcanic island arc
complex.
Sea level rose and fell,
repeatedly, over a land
surface of low relief.
Several small
depositional basins
developed where the
crust was subsiding.
Most sediments
deposited in southern
Ontario were marine
limestones and shales.
Silurian Period
North America and
Europe joined (completing
the central and northern
Appalachians) by the end
of the Silurian.
The Siberian/Asian
continent was converging
on Europe.
The North America/Europe
continent began to
approach Gondwanaland.
An extensive trench and volcanic arc developed along the east coast
of North America.
Taconialand was the growing mountain range that was forming due
to compressive forces associated with convergence of North America
and Europe.
Southern Ontario received shales and sandstones that were eroded
from the rising mountains.
55% of the natural gas produced in Ontario comes from Silurian
sandstones.
In later Silurian time mountain building diminished and limestones
were deposited in southern Ontario.
Rocks exposed along the Niagara Escarpment are all of Silurian age.
Much of western Canada was covered by a shallow sea in which
limestones were deposited.
Devonian Period
Continued approach of
North America towards
Gondwanaland.
N. America, Europe, Asia
and Siberia were beginning
to form a second
supercontinent: Laurasia.
An extensive mountain belt
had developed all along the
eastern margin of North
America.
Sea level was very high and
much of North America
was covered by a shallow
sea.
Southern Ontario was
covered by a shallow sea in
which limestones and
evaporites (halite and
gypsum) were deposited
Important economic
deposits for oil and gas, salt
and gypsum.
Extensive limestones and
salts were deposited
throughout western
Canada.
A large limestone reef complex extended over much of Alberta.
These reef deposits are
important sources of oil and
gas today.
Oceanic crust continued to
subduct along the west coast
of North America (volcanic
arc complex).
Carboniferous Period
Continents continue to come together.
African Gondwanaland
collided with North America
forming the southern
Appalachian Mountains.
Much land mass near
equator: abundant land
plants, increased
atmospheric O2.
Most of North America was
covered by shallow seas or
swampy lowlands.
Much of North America’s
coal deposits were formed at
this time.
Permian Period
Asia collides with Europe
to form the Ural
Mountains.
One large supercontinent
(called Pangea) forms with
the merging of Laurasia
and Gondwanaland.
Most of eastern North America was dry land, the west was a shallow
sea.
An outcome of the coming
together of the large
landmass: extensive
weathering, removing CO2
from the atmosphere.
Loss of CO2 reduced global
temperature.
Extensive volcanism in Siberia (related to collision): Siberian Traps,
a flood of basaltic lava, 2 million cubic kilometres.
This extensive volcanic
activity may have produced
dust that further reduced
the Earth’s temperature.
Lands were dry and cool,
reducing plant cover and
reducing O2 in the
atmosphere.
Sea level was particularly low.
Permian ended with the most
dramatic mass extinction in
Earth history: up to 95
percent of marine life died off.
Pangea persisted and a second
major mass extinction marks
the end of the Triassic Period.
Jurassic Period
Pangea began to break up
with the rifting of North
America, drifting to the
northwest.
Atlantic Ocean began to open.
Sea level began to rise and
global temperatures
continued to become
warmer.
Period of rapid
diversification of organisms
and the dinosaurs became
the dominant group.
The Rocky Mountains
began to rise up and
shallow seas moved both
north and south across
much of central North
America.
Cretaceous Period
Continents continued to
move apart.
The Rocky Mountains
went through a major
period of construction in
the Early Cretaceous.
Small land masses on the
subducting Pacific Plate
collided with North
America.
Extensive volcanism and intrusion took place all along the western
edge of North America.
Volcanic ash beds several
centimetres thick are found
thousands of kilometres
from the volcanic sources
(massive explosions).
Sea level continued to rise to
the mid-Cretaceous and then
began to fall.
Central North America
flooded by a sea extending
from the Arctic Ocean to
the Gulf of Mexico (Western
North American Seaway).
Sandstones and shales were
shed off the rising
mountains, into the seaway.
Dinosaurs dominated until
the end of the mass extinction
at the end of the Cretaceous.
Cenozoic Era
North & South America,
Australia and Antarctica
spread away from
Pangea, further opening
the Atlantic Ocean.
Africa collided with
Europe; India collided
with Asia.
The early Cenozoic was
another period of
mountain building in the
Rocky Mountains (more
small collisions).
Mammals diversified and
became the dominant
group of organisms.
4 Billion years from now………..
The sun explodes, Earth is finished….