Download Unit1continetaldrift 3.40MB 2017-03-29 12:41:28

Unit 1: Physical Environments
1.1 Earth Systems – The Earth’s crust is part of a dynamic system.
Continental Drift:
Continental drift is the theory that the continental landmasses have changed position over time, attributed to Alfred
Wegener (A German meteorologist) in 1912.
The evidence for this movement falls into three categories – Geological / Biological / Climatological.
Evidence for Continental Drift:
Geological:
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The “fit” of the continents – similar to a jigsaw.
o comparing continents either side of the Atlantic – South America and Africa
o Especially when using the edges of the continental shelves rather than present coastline.
Rock types / structures are similar on the two sides of the Atlantic.
o Sequence of sedimentary and igneous rocks from the Appalachian Mountains of North America match
the Caledonian Mountains of Scotland.
o Ancient Shield Mountains can be traced from East Brazil to West Africa.
Biological:
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Fossils found in South America and West Africa, suggests these continents were once
together.
o Mesosaurus – a small freshwater reptile
o Glossopteris – small fern
o Cynagnathus – Triassic reptile
Plant / animal species diversification.
o Mammals found in South America, Africa and Australia are uniquely different – developed
under different circumstances – continental drift.
o As continents join – the Americas – species of plants / animals shared.
Climatological:
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Coal / Oil found in Antarctica
Glacial characteristics in warm regions
o Glacial striations in Brazil match those in West Africa.
o Glacial deposits in India, South America and the Vaal Valley in South Africa are similar.
Students Notes – Lesson 1
Plate Tectonics:
As Wegener developed his ideas on the movement of continents it became clear that about 300 million years ago the continents were a single landmass called
Pangaea. Over the next 100 million years this landmass drifted apart forming two distinct regions:
 Laurasia – In the Northern Hemisphere, made up of Eurasia and North America
 Gondwanaland – In the Southern Hemisphere, made up of Africa, Australasia, India, South America and Antarctica.
See clip on Pangaea – Make annotated diagram/s on Pangaea and movement.
http://svs.gsfc.nasa.gov/vis/a000000/a000000/a000073/a000073.mpg
http://whs.moodledo.co.uk/file.php/1365/EarthSystems/Earth%20Systems/The%20Break-up%20of%20Pangaea.swf
http://whs.moodledo.co.uk/file.php/1365/EarthSystems/Earth%20Systems/The%20Break%20up%20of%20Pangaea.swf
Wegener’s studies eventually led to the formulation of the PLATE TECTONIC theory. This states that the Earth’s crust is not a continuous skin but a series of
rigid, spherical caps about 100km thick. Of these seven are very large and five carry continents. See diagram A on the next sheet. The plates ride on a weak, soft,
partially upper mantle.
The main evidence to support this idea comes from investigations into sea-floor spreading, which is occurring in the Atlantic Ocean.
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Palaeomagnetism of the basalts.
o When magma solidifies the iron particles are orientated to magnetic north.
o The North & South Poles move considerably during geological time – even
reversing.
o This is known as Polar Wandering.
o The pattern of magnetism is reflected either side of the Atlantic Ridge, and
relates to the alternating pattern of Northerly & Southerly magnetism.
o http://whs.moodledo.co.uk/file.php/1365/EarthSystems/Earth%20Sys
tems/Magnetic%20Reversal.swf
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Age of rocks on the sea-floor.
o Near the mid-Atlantic ridge the basaltic rocks of the sea floor are much
younger than those found towards the continental shelves at the edge of the
ocean.
o The age of the rocks either side of the mid-Atlantic ridge mirror each other,
suggesting they were once touching.
Diagram A