1.a. There is a variety of evidence for the theories of continental drift and plate tectonics. Flashcards
Outline the basic structure of the Earth.
Made from 3 primary concentric layers.
Studies of earthquake waves being transmitted through the Earth show that there is a concentric structure to the Earth’s interior.
Outline the mean, minimum, and maximum thickness of continental crust.
Mean: 35 km.
Minimum: ~30 km.
Maximum: 70 km.
Outline the thickness of oceanic crust.
5-10 km.
Outline the thickness of the mantle.
From 10-35 km, down to 2900 km.
Outline the density of continental and oceanic crust.
Continental: 2.6-2.7 kg/m3.
Oceanic: 3.0 kg/m3.
Outline the density of the mantle at Moho, and at the CMB.
Moho: 3.3 kg/m3.
CMB: 5.6 kg/m3.
Outline the mineral composition of continental and oceanic crust.
Continental: Granite, silicon, aluminium (sial).
Oceanic: Basaltic, silicon, magnesium (sima).
Outline the mineral composition of the mantle.
Rich in magnesium and iron.
What makes up oceanic and continental plates?
Lithosphere and crust.
Outline the Mohorovicic Discontinuity
The boundary zone between Earth’s crust and the mantle.
This boundary marks a change in seismic-wave velocity from the crust to the uppermost mantle within the lithospheric plate.
Depth varies from 35km below the surface at the continents, whilst just between 5 and 15km below the oceans.
Outline the core-mantle boundary.
The core and mantle are separated by a distinct boundary at a depth of about 2900km.
What is confining pressure?
Pressure increasing with depth, (towards the core).
Outline the upper mantle.
Consists of two layers.
Lithosphere and the asthenosphere.
Outline the lithosphere.
A rigid layer sandwiched between the crust and the asthenosphere.
Rocks are cold and brittle.
Varies in thickness, and its boundary with the asthenosphere is difficult to define precisely; this is due to confining pressure and thus plastic flow in the rocks.
Outline the asthenosphere.
Extends from 100km down too 300km.
Rocks are put under such pressure that they flow like a liquid, (plastic flow).
Convection currents also exist; due to vast amounts of heat generated deep in the mantle.
As a result, the asthenosphere flows carrying with it the solid lithosphere and crust above.
What were the most devastating earthquakes?
Haiti, 2010: 222,570 dead.
Shansi, 1556: 830,000 dead (questionable validity - centuries ago).
What were the most devastating volcanoes?
Tambora, 1815: 92,000 dead.
What happened to continental theories in the 18th Century?
(Continental Drift and the Theory of Plate Tectonics)
During the 18th Century, maps of the world became more accurate and widely distributed.
The shapes of the continents and their relationships to each other attracted interest.
Who was Alexander von Humboldt? What did he write about in 1801?
(Continental Drift and the Theory of Plate Tectonics)
German geographer and explorer.
In 1801, he wrote about the apparent fit between northeast South America and the west coast of Africa.
However, it was not until over 100 years later that ideas concerning the fit of the continents received serious attention.
What did Wegener do in 1912?
(Continental Drift and the Theory of Plate Tectonics)
In 1912, he made a comprehensive case for continental drift and worked on his ideas until his death in 1930.
Outline Wegener’s 1912 proposal.
(Continental Drift and the Theory of Plate Tectonics)
Based on the theory that in the Carboniferous period, 250 million years ago, a single large continent (Pangaea) existed.
Wegener suggested that Pangea broke apart into two large land masses.
Laurasia in the northern hemisphere, and Gondwanaland in the southern hemisphere.
The theory concluded by stating that this movement continued until the present day, spreading the continents across the globe.
What was missing from Wegener’s theory of continental drift?
(Continental Drift and the Theory of Plate Tectonics)
A mechanism and explanation for how the continents drifted.
Wegner couldn’t tell the scientific community how the plates move.
Outline 2 pieces of geological evidence from Wegener’s theory of continental drift.
(Continental Drift and the Theory of Plate Tectonics)
The fit of continents such as South America and Africa on either side of the Atlantic.
Evidence from about 290 million years ago of the effects of contemporaneous glaciation in southern Africa, Australia, South America, India and Antarctica, suggesting that these land masses were joined at this time, located close to the South Pole.
Mountain chains and some rock sequences on either side of oceans show great similarity, e.g. northeast Canada and northern Scotland.
Outline 2 pieces of biological evidence from Wegener’s theory of continental drift.
(Continental Drift and the Theory of Plate Tectonics)
Similar fossil brachiopods (marine shellfish) found in Australian and Indian limestones.
Similar fossil animals found in South America and Australia, especially marsupials.
Fossils from rocks younger than the Carboniferous period, in places such as Australia and India, showing fewer similarities, suggesting that they followed different evolutionary paths.
