Transcript C1b 6.2 The restless earth

The restless earth
The earth as it
appeared 65 million
years ago
Early Geologists missed the
most obvious observation
that Africa’s coast line
closely matched the coast
line of South America
The mantel behaves
like a solid but can
flow slowly like a liquid
A moving plate
Heat from radioactive decay
in the core
1915
Alfred Wegener first put forward
the idea of continental drift
but he could not explain it.
It was rejected by the
other geologists!
Heat from radioactive decay
in the core
One land mass ‘Pangeae’
Pangaea splits in two
Land masses move apart
- 4cm year?
India moves North and
pushes up the Himalayas
Land masses are cracked into a large number of tectonic plates
The distribution of volcanoes largely follows the plate boundaries
If earthquakes happen under the sea,
huge tidal waves called tsunamis may occur.
If earthquakes happen under the sea,
huge tidal waves called tsunamis may occur.
If earthquakes happen under the sea,
huge tidal waves called tsunamis may occur.
Problems e Problems emerged with the cooling earth idea...
1. Too much heat existed in the core from radioactive elements to
allow for cooling
effect
2. Eventually all mountains should be eroded and all dips filled in
and be of a similar age
3. Where did all the eroded river sediment go?
- 500 million tons of it each year!
- a 20km high!coverage around the planet !
1. Similar fossils and rocks appeared on coasts of South America
and Africa
5. How did identical snails turn up in Norway and Canada and how
did marsupials travel from South America to Australia?
Problems e Problems emerged with the cooling earth idea...
1. Too much heat existed in the core from radioactive elements to
allow for cooling
effect
2. Eventually all mountains should be eroded and all dips filled in
and be of a similar age
3. Where did all the eroded river sediment go?
- 500 million tons of it each year!
- a 20km high!coverage around the planet !
1. Similar fossils and rocks appeared on coasts of South America
and Africa
2. Identical snails turn up in Norway and Canada and marsupials
end up in South America and Australia.
Problems e Problems emerged with the cooling earth idea...
1. Too much heat existed in the core from radioactive elements to
allow for cooling
effect
2. Eventually all mountains should be eroded and all dips filled in
and be of a similar age
3. Where did all the eroded river sediment go?
- 500 million tons of it each year!
- a 20km high!coverage around the planet !
1. Similar fossils and rocks appeared on coasts of South America
and Africa
2. Identical snails turn up in Norway and Canada and marsupials
end up in South America and Australia.
3. There coal seams from tropical forests in Spitzbergen
in the arctic circle.
Problems e Problems emerged with the cooling earth idea...
1. Too much heat existed in the core from radioactive elements to
allow for cooling
effect
2. Eventually all mountains should be eroded and all dips filled in
and be of a similar age
3. Where did all the eroded river sediment go?
- 500 million tons of it each year!
- a 20km high!coverage around the planet !
1. Similar fossils and rocks appeared on coasts of South America
and Africa
2. Identical snails turn up in Norway and Canada and marsupials
end up in South America and Australia.
3. There coal seams from tropical forests in Spitzbergen
in the arctic circle.
Early geologists invented “ land bridges” across prehistoric seas to allow
animal migration which since have disappeared!! (No evidence existed for this at all)
People once thought that the oceans and the continents were formed by
shrinkage from when the Earth cooled down after being formed.
Tectonic theory
Alfred Wegener proposed something different. Consider Africa and South
America:
These continents look
like they “fit”
together. They also
have similar rock
patterns and fossil
records. These two
pieces of evidence led
me to believe that
there was once a single
land mass. This is my
TECTONIC THEORY.
Forming mountains
The formation of mountain ranges can be explained by tectonic
theory. Consider the Himalayas at the top of India:
This is where
India is now
This is where
India was millions
of years ago
The intense heat and pressure from this process causes the
rocks to change structure into metamorphic rocks.
The Evidence:
Tectonic theory
1) Some continents look like they used to “fit” together
2) Similar rock patterns and fossil records
The Problems:
Wegener couldn't explain
how continental drift
happened so nobody
believed him
The Answer:
1) Scientists discovered 50 years later that the Earth generates massive
amounts of heat through radioactive decay in the core. This heat
generated convection currents in the mantle causing the crust to move
2) We also now know that the sea floor is spreading outwards from plate
boundaries
Conclusion – scientists now believe Wegener’s Tectonic Theory