Science Focus Topic 4 Notes: The Moving Crust | Print |
The Earth's Interior
crust is the top layer of the Earth. Below it is the mantle, which is made of rock material (upper part is solid, lower part is partly melted. The upper mantle and crust are called the lithosphere. Below the mantle is the core. The outer core is made up of mainly liquid iron and nickel, while the inner core is solid.

Evidence for Continental Drift

- Alfred Wegener
( ) collected evidence to explain the various shapes of the continents and how they were all together at one time.

Biological Evidence

- fossil evidence was found on different continents, like mesosaurus, kannemeyerid and lystrosaurus (see map on p. 383)
- along with the fossils and the interlocking shapes of the continents, Wegener concluded that the continents were joined together as one supercontinent
pangaea (pangea).
( )
- his explanation is called the
Theory of Continental Drift.

Evidence from Rocks

Mountain ranges were also compared:
- the Appalacian in North America and the range in Britain and Norway were made of the same kind and age of rock
Trilobites in the Himalayas suggested that India was once part of Antarctica, which broke off and collided with Eurasia, putting the fossils of trilobites, from the bottom of the sea, high into the Himalayans.

Geological Evidence of Climate

- coal provided more evidence, because in order for it to form, a rich tropical plant environment must have been present - coal is found in moderate to cold climates
- evidence of even greater climatic changes were found in places likely covered by glaciers (these places are now far too warm to support the presence of glaciers), this suggested that the continents may have once been part of the south pole.

Response to Wegener

- after his findings were published, in a book called The Origin of the Continents and Oceans, Wegener's ideas were rejected, because the scientific community did not agree with his assumptions and explanation that the moon might be responsible for the movement of the continents.
- after his death, advances in new technology and the work of a Canadian Scientist led to a new theory that explained Wegener's observations

Advances in New Technology

- sonar (sound wave technology) identified the Mid-Atlantic Ridge
magnetometers (electronic instruments that detect the direction and strength of a magnetic field) the magnetic field in the Atlantic sometimes pointed south, instead of north (these were called reversal strips)
- igneous rock contains
magnetite, which lines itself with the Earth's magnetic field, as the rock hardens on the surface, the mineral particles maintain their alignment with the magnetic field, indicating that the reversal strips must have formed at a different time
- the pattern of magnetic reversal strips along the Mid-Atlantic Ridge meant the sea floor was spreading, leading to the
Theory of Sea Floor Spreading. (as new rock forms, it takes on the magnetic polarity of the the Earth at the time of formation)

Deep Sea Drilling

- confirmation of the theory of sea floor spreading was provided by the ship, Glomar Challenger, which brought drill samples up from the ocean floor (younger rock was closer to the ridge and older rock was closer to the continents)
- lava that cools very quickly on the ocean floor is called '
pillow lava'.

The Theory of Plate Tectonics

All the evidence collected indicates that the Earth's crust is broken up into plates (see Figure 5.43, p. 390), which are moving on the Earth's mantle. The new theory is called the Theory of Plate Tectonics. Plates pushing together are called converging plates, whereas plates pulling aprt are called diverging plates. Tuzo J. Wilson (a Canadian Scientist) helped form this new theory, by suggesting the plates slide past each other.

Convection Currents

- a convection current is the circular flow within a fluid that is caused by the rising of warmer particles and sinking of cooler particles
- scientists believe it is this action, within the mantle, which is causing the plates to move
- the plates that collide, or converge have one plate above and the other below (these places are called
subduction zones)
- subduction zones occur where the convection currents, in the mantle, cool and sink


- a unifying theory is one which explains several different natural events and landforms (volcanoes, earthquakes and mountains)
Sound Navigation and Ranging (SONAR)
self-contained underwater breathing apparatus (SCUBA)
- Submersibles are small submarines that enable divers to go deeper, protecting them from the pressure of the water
- satellites and lasers are used to measure incremental change (change that happens slowly) in plate movements
- '
black smokers' are deep-sea (ocean floor) vents, where tube worms use the sulphur from the vents as an energy source