Pangea
- Created by: broog
- Created on: 08-04-15 11:02
Plate tectonics Theory: Alfred Wengners early idea
Plant Fossils
Description
Fossils of warm climate ferns have been found in India and Antarctica.
Discussion
- The existence of warm currents around Antarctica at some point may have led to a warmer climate
- The climates could have changed
- For Antarctica to be hot the equator would have been too hot to sustain life.
Plate tectonics Theory: Alfred Wengners early idea
Coal and Oil in Antarctica
Description
Massive coal and oil reserves under Antarctica suggest large amounts of vegetation and animal life were once here.
Discussion
- Warm water currents may have heated the climate.
- Climates may have been different
- Antarctica as a land mass may have been located closer to the equator.
Plate tectonics Theory: Alfred Wengners early idea
Glacial Striations
Description
These have been found in Brazil and West Africa. Glacial deposits have been found in India and South America suggesting that these were once cooler climates
Discussion
- Different climate
- Can only have been formed by Glaciers so these places must have been located in a cooler climate.
Plate tectonics Theory: Alfred Wengners early idea
Continental Drift
This is the theory that the continents were once a super continent called Pangea.
It was first noticed by Francis Bacon in the 17th Century - 'Jigsaw fit'
It is largly attributed to Alfred Wegner who wrote a paper in 1912 containg evidence to support the theory.
Modern Evidence:
- Seismic, volcanic and geothermal activity on plate boundaries
- Ocean ridges
- Mountains increasing in height
Kevin Mansfield's Earth formation hypothesis
This hypothesis states that the Earth was formed by the collision of two planets:
- PreEarth
- Old Moon
Old Moon (the smaller one) was 'swallowed' by PreEarth and the combined gravity of the two planets held Old Moon in the centre of PreEarth.
Evidence:
- The hole in the North West Pacific - where Old Moon entered
It is an area of the sea bed which is much deeper than avarage. When impact happend it forced apart the Americas and Europe/Africa which explains the 'Jigsaw fit'
- The Ring of Fire - Impact mountains
These were originally thought to have made a whole circle but the impact caused the PreEarth to expand and forced the circle apart across the Phillipines, Japan, Alaska, South America, Antarctic Peninsula, Southern Alpes of New Zeland and the submerged Colville and Kermadec.
Expanding Earth theory
This theory tries to explain continental drift by suggesting that the Earh is constantly expanding as shown by the Ocean ridges.
Evidence:
- The Ocean ridge off the coast of australia is the same shape as the West coast of South America.
- 'Jigsaw fit' - but mechanism for movement is the expanding Earth
- Insinuates that there is only convergent plate boundaries so new land is always created.
Shock Dynamics theory
This suggests that all landforms on the planet were made in the same event. Suggests that a block of land made upof India, Australia and South East Asia hit Asia and caused it to shatter into smaller pieces such as the Phillipines and Borneo.
It also suggests that Ocean trenches were made in this event. These trenches then caused down drafts which further pulled land into the places that it can be found in now.
This theory has flaws and is unable to sugest a mechanism for the movement of the plates.
Sea floor mapping
Land is created at conservative plate boundaries such as at the Mid atlantic Ridge.
In 1984 Maurice Ewing examind a group of islands in the Atlantic ocean.
He discovered hat the islands were the highest points along a mountian range hidden under the sea (a chain)
The range was made up of young rock.
Palaeomagnatism
Rock record the polarity of the Earth.
The magma rises and the metalic elements face North, then hardens.
As the poles reverse, the rock changes to fae the new North creating strips of rock facing each North adn recording it.
metalic, iron rich elements are magnatised in the direction of the field.
It reverses every 400,000 years
The patterns formed relate to the alternating field.
palaeomagnatism of basalts suggests that rock has been moving away from the ridge.
Age of ocean floor
In 1962 harry Hess proved that the newest rocks under the Atlantic were next to the Mid Atlantic Ridge.
The oldest ones were nearest to the coast of the USA.
He concluded that the sea floor was slowly moving outwards from the ridge.
Evidence for Continental drift
Sea floor spreading
Palaeomagnatism
Age of ocean floor
Distribution of seismic events
Satelite measuring or continents
Earth isn't expanding - subduction - marianus trench
Evidence for Plate Tectonics theory
'Jigsaw fit'
Rock structure
Animal fossils
Plant fossils
Coal and oil in Antarctica
Glacial striations
Plate Margins: Constructive (Divergent)
Movement of plates
The plates are moving towards each other.
Tectonic features
New crust is formed from upwelling magma. Features:
- mid-oceanic ridges
- effusive ridge (shield) volcanoes
- Shallow focus earthquakes
- median rift valleys
- continental rift valleys
Examples
- Mid Atlantic Ridge
- East African Rift Valley
Plate Margins: Destructive (convergent) subduction
Movement of plates
Two plates moving away from each other.
Tectonic features
Oceanic to Oceanic:
- trenches
- island arcs
- explosive volcanoes
- earthquakes
Examples
On the margins of the Pacific plate, with subduction under other seperate sections of the plate, Tonga trench
Plate Margins: Destructive (convergent) subduction
Movement of plates
Two plates moving away from each other.
Tectonic features
Oceanic to Continental:
- trenches
- fold mountains
- explosive volcanoes
- earthquakes
Examples
Andean type: Nazca plate subducting under South American plate
Plate Margins: Destructive (convergent) Collision
Movement of plates
Two plates moving away from each other.
Tectonic features
Continental to Continental:
- fold mountains
- shallow focus Earthquakes
Examples
Himalayan type: Indian plate colliding with the Eurasian plate.
Plate Margins: Conservative (transform)
Movement of plates
Two plates shearing past each other.
Tectonic features
Shallow focus earthquakes
Examples
San Andreas fault - Pacific plate and the American plate
Plate Margins: not on a margin
Movement of plates
Hot spots: may be near the centre of a plate
Tectonic features
Plume volcanoes
Examples
Hawaiian islands: Emperor seamount chain.
Plate Tectonic theory
This term was devised by geologists Mackenzie and Plamer
The earths crust is believed to be split into a number of different plates which consits of a mixture of oceanic and continental crust.
There are over 50 plates moving at different rates in different directions
All plates are in motion.
Constructive plate margin: East African Rift Valle
This is an example of a constructive margin on an area of continental crust.
eastern Africa is moving in a North Easterly direction, diverging from the main African plate which is moving North.
The valley (consisting of two parallel rifts extends for 4000km from Mozambique to the Red Sea.
How it formed:
As the plates pull apart, the crust is subjected to huge pressures causing fracturing and fault lines
Sections of crust between parrallel fault lines then drop down.
The area experiences volcanic activity suggesting that the lithosphere has been weakend and thinned by tension, resulting in rising magma escaping onto the surface at volcanoes such as mount Kilimanjaro.
Constructive plate margin: Ocean Ridges
Ocean ridges are the longest continuous uplifted features on the suface of the planet.
There total combine length reaches 60,000km)
In some parts they rise up to 3,000 metres above the sea floor.
Their form depends on the rate at which the plates are pulling apart.
Slow rate (10-15 mm per year):
- wide ridge (30-50 km)
- depp central rift valley (3,000 m)
- Inward facing fault scrapes
Intermediate rate (50-90 mm per year):
- Galapagos ridge
- smoother outline
- less well marked rift (50-200 m deep)
Constructive plate margin: Ocean Ridges (2)
Rapid rate (> 90 mm per year):
- smooth crest
- no rift
- Pacific Rise
Volcanic activity also occurs along the ridge, forming submarine volcaneos. these sometimes rise above sea level after successive eruptions e.g. Surtsy (South Iceland 1963)
These volcanoes have gentle sides because of the low viscosity of basaltic lava
Eruptions are frequent and gentle (effusive)
Constructive plate margin: Ocean Ridges (3)
As new crust forms and spreads outwards, transform faults occur at right angles to the plate boundary.
Spreading plates on either side of these faults may move at different rates leading to friction and shallow focus earthquakes.
Comments
No comments have yet been made