Continental Drift Theory by Alfred Wegener
In 1915, the German geologist and meteorologist
Alfred Wegener first presented the theory of continental drift, which
states that parts of the Earth's crust slowly drift apart . The fossil record supports and gives acceptance to the theories of continental drift and plate tectonics. But it took a long time for the idea to become accepted by other scientists
states that parts of the Earth's crust slowly drift apart . The fossil record supports and gives acceptance to the theories of continental drift and plate tectonics. But it took a long time for the idea to become accepted by other scientists
Wegener’s evidence for continental drift
Theory :-
Theory :-
· Same types of fossils of animals and plants are
found in South America and Africa .
· The shape of the east coast of South America fits the
west coast of Africa .
· Matching rock formations and mountain chains are found
in South America and Africa .
Wegener presented
his ideas at a
conference in 1912,
and then published
them in a book in 1915 .Wegener’s
ideas could certainly explain similar
fossils in different continents,
but other geologists thought that
there were once ‘land bridges’
between continents, allowing animals
to travel between them.
them in a book in 1915 .Wegener’s
ideas could certainly explain similar
fossils in different continents,
but other geologists thought that
there were once ‘land bridges’
between continents, allowing animals
to travel between them.
Wegener was
trained as an astronomer and a meteorologist. Many geologists did not think that he had
the right background to judge geological
theories.
Wegener
hypothesized that there was a gigantic supercontinent
200 million years ago, which he named Pangaea, meaning "All-earth".
Pangaea started to
break up into two smaller supercontinents,
called Laurasia and Gondwanaland, during the Jurassic period. By the end of the Cretaceous
period, the continents were separating into land masses that look like our
modern-day continents.
Wegener published Continental Drift Theory in his 1915 book, On the
Origin of Continents and Oceans. In it he also proposed the existence of the super continent and named Pangaea (means
"all the land" in Greek).
Fossil Evidence
in Support of the Theory
Glossopteris, a
tree-like plant from the Permian Period through the Triassic Period. It had
tongue-shaped leaves and was about 12 ft
(3.7 m) tall. It was the dominant plant of Gondwana. Eduard Suess was an Austrian geologist who
first realized that there had once been a land bridge connecting South America, Africa, India, Australia, and Antarctica.
He named this large land mass Gondwanaland
(named after a district in India where the fossil plant Glossopteris was found). This was the southern supercontinent formed
after Pangaea broke up during the Jurassic period. Suess based his deductions on the fossil plant Glossopteris, which is found throughout
India, South America, southern Africa, Australia, and Antarctica.
Fossils of Mesosaurus
(one of the first marine reptiles, even older than the dinosaurs) were found in
both South America and South Africa. These finds, plus the study of
sedimentation and the fossil plant Glossopteris
in these southern continents led Alexander
duToit, a South African scientist, to support & strengthen the idea of the
past existence of a supercontinent in the southern hemisphere, Eduard Suess's Gondwanaland. This further support to Alfred Wegener's Continental Drift Theory
The Earth's crust is divided into huge, thick
plates that drift atop the soft mantle.
The plates are made of rock and are from 50
to 250 miles (80 to 400 km) thick. They move both horizontally and
vertically. Over long periods of time, the plates also change in size as their
margins are added to, crushed together, or pushed back into the Earth's mantle.
PLATE
TECTONICS
The theory of plate
tectonics (meaning "plate
structure") was developed in the 1960's.
This theory explains the movement of the Earth's plates (which has since been
documented scientifically) and also explains the cause of earthquakes, volcanoes,
oceanic trenches, mountain range formation, and other geologic phenomenon.
The plates are moving at a speed that has been estimated at 1 to 10 cm per year. Most of the
Earth's seismic activity (volcanos and earthquakes) occurs at the plate
boundaries as they interact.
The top layers of the plates
are called the crust. Oceanic crust (the crust under the oceans) is thinner and denser than
continental crust. Crust is constantly being created and destroyed; oceanic crust is more active than continental
crust.
TYPES OF
PLATE MOVEMENT :
Divergence, Convergence, and Lateral Slipping
At the boundaries of the plates,
various deformations occur as the
plates interact; they separate from one another (seafloor spreading), collide
(forming mountain ranges), slip past one another (subduction zones, in which
plates undergo destruction and remelting), and slip laterally.
The current continental
and oceanic plates include: the Eurasian
plate, Australian-Indian plate, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos
plate, North American plates, Caribbean plate, South American plate, African
plate, Arabian plate, and the Antarctic plate. These plates consist of
smaller sub-plates.
Since the Earth's crust solidified billions of years ago, plates of its crust have been drifting all over the globe . The map of the Earth is always changing; not only are the underlying plates moving, but the plates change in size. Also, the sea level changes over time (as the temperature on Earth varies and the poles melt or freeze to varied extents), covering or exposing different amounts of crust .
Since the Earth's crust solidified billions of years ago, plates of its crust have been drifting all over the globe . The map of the Earth is always changing; not only are the underlying plates moving, but the plates change in size. Also, the sea level changes over time (as the temperature on Earth varies and the poles melt or freeze to varied extents), covering or exposing different amounts of crust .
Although much of this supporting evidence for continental drift was
known and available for many years, the concept received little acceptance and
in fact open derision, until researchers began to formulate explanations for
the mechanisms of movement. Pieces of information from many sources were
assembled over time to develop a uniform concept. An understanding of the
importance of convection currents in the mantle goes back to the Dutch
researcher Felix Menesz in 1930, long before any kind of acceptance of that idea. In 1959 Maurice Ewing, Bruce Heezen, and Maria Tharp used
echo-sounding profiles to draw a topographical map of the North Atlantic floor.
The plotting of the data produced a map that stunningly revealed the extent of
the Mid-Atlantic Ridge and the presence of a deep central rift within. Harry Hess work, History of Ocean Basins, described sea-floor spreading
in 1960; and in 1963 Fred Vine and Drummond Matthews wrote about the geomagnetism of the Indian Ocean. Tuzo Wilson in 1965 proposed an explanation for the
movements of transform faults along the rift zone and in 1968 W. Jason Morgan produced mathematical support for the possibilities of plate
movements. In 1968 also, Bryan Isacks, Jack Oliver, and Lynn Sykes plotted the
occurrences of shallow and deep focus earthquakes
along the plate edges.
References :- enchantedlearning.com , https://en.wikipedia.org/wiki/Continental_drift ,
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