Plate Tectonics
Plate tectonics
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A theory that states that the earth’s crust is
made up of a number of plates which move
over a liquid crust that get created and
destroyed over time.
Moving Plates
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The force for these movements is derived from
magmatic convection cells in the
asthenosphere of the mantle.
The upward portion of these cells are known as
magmatic plumes.
When they hit the crust, the plate above is
melted and forced to spread creating a
spreading ridge as they are adding new
continental material (constructive margin) to
the edges of these plates.
Evidence supporting plate tectonics
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Ages of oceanic crusts get older as one moves away
from a spreading ridge.
Ages of oceanic sediments on top of the crust gets
older as one moves away from a spreading ridge.
Rock formations with the same mineral content and
age existing on opposite continental shores. The
eastern most tip of south America and the African
Congo both have the same iron ore rock formation.
Rock formations are also shared between
Newfoundland, Canada and the west coast of Ireland
and southern India and South Africa.
Evidence supporting plate tectonics
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Stationary hot-spots "burn" trails into moving
continents.
Magnetic anomalies showing variations in the
Earth’s magnetic field strength are arranged in
bands parallel to each other on either side of
the spreading ridges.
Evidence supporting plate tectonics
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Magnetic polarity reversals patterns are
preserved as the rock formed, show symmetry
about spreading ridges.
The margins or edges of some continents have
shapes that indicate that they once fit together.
(i.e. South America fitting into Africa.)
Evolution and Biodiversity
Influenced by Plate Activity
Pangea
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Two hundred million years ago (Ma), research
suggests that all the continents where one large
mass which was named Pangea.
Terrestrial organisms were able to migrate
across all the continents and were only limited
by their biotic potential.
Biodiversity
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As Pangea began to separate into separate
continents 130 Ma, creating physical barriers
such as seas, restricting migration to within the
continents.
Gene pools of species are separated and as
they are exposed to different physical (i.e.
climate) and biotic (i.e. change in predators)
conditions, each portion of the species adapts
differently and eventually forms new species
on the separated continents.
This process is known as speciation.
Biodiversity
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Changes in physical and biotic conditions will
also lead to the creation of new species
increasing the diversity of habitats and niches.
This also provides the space for new species to
evolve into these habitats.
The end result of the separation of Pangea into
today’s continental configuration is that plate
tectonics has been one of the main driving
forces promoting biodiversity or organisms.
Biodiversity
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In addition to continents separating, some like India
left south Africa and Antarctica and joined up with
Asia.
It took with it organisms that were typical to
Antarctica and Australia.
Over the next 100 Myrs these organisms evolved in
isolation from any other continent until it formed a
land bridge with Asia.
Since 30 Myrs ago the species on India and Asia have
been re-adapting themselves causing additional
biodiversity.
Biodiversity
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Australia has one of the most unique sets of organisms as it
and Antarctica have been separate from all the other continents
for the last 130 Myrs.
Australia separated from Antarctica about 50 Myrs ago.
This extreme isolation over such a long period of time
supports Darwin’s theory of evolution in that this part of the
world has the most unique organisms.
Australian species have had such limited contact with species
from other continents that they have only needed to adapt to
their particular set of species and climate.
No re-adaptation to other species from other continents has
occurred until the arrival of the Europeans.
Biodiversity
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The splitting up of Pangea 200 million years
ago had the following effects on species
diversity and distribution.
a) Species gene pools or populations where
split as Pangea separated.
b) New habitats were created due to a
change in biotic and abiotic factors such as
climate (temperature and moisture), changes in
species relationships, and topography.
Biodiversity
c) New niches were made available and filled causing further
adaptation of species to new conditions thus modifying the
local ecosystem.
d) Species relationships change with respect to mutualism,
predation, and competition. Species need to modify food
source, protection, and dependence patterns in the food
web.
e) Speciation: is the creation of a new species when a gene
pool of one species is split, exposed to new conditions to
which each pool adjusts to. Different genetic traits are
passed on to offspring. A new species evolves once the 2
original populations cannot mate.
Biodiversity
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Rejoining of plates such as India and Asia. 30 Ma ago caused
the following.
a) Migration of one species into the territory of another
introduces new forms of competition and predation that
existing species need to adapt.
b) Further speciation is generated and modified as they
come into contact with a variation of the original gene pool.
Biodiversity
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Extreme isolation such as Australia and Antarctica.
130 Ma of isolation.
a) As no new predators are introduced over a long
period of time speciation is limited to changes in
abiotic factors such as climate and topography.
b) Evolution tends to slow down and become
more specialized if there are fewer stresses and
ecosystem changes.
c) Species evolve separately from original gene
pool and tend to be very different from other areas
with more contact with the original gene pool.