Plate Tectonic Supercycle 5.3

Question 1

Formation of Australia?

Answer 1

Sea floor sediment destroyed in each super cycle > evidence of pre-pangaea comes from continent plates: (next slide)

Question 2

Cratons in Australia?

Answer 2

• a surviving chunk of continental rock
• Aus has oldest cartoons on Earth
• oldest were already carbonised by 2500 mya > been through 10 super cycles

Question 3

Impacts of plate tectonics on sea levels?

Answer 3

Sea levels determined by presence of ice caps HOWEVER other causes at work:
-Av depth for MOR is 2500 m and seafloor 50 my old is 5000 m deep
>reason for this =as oceanic crust gets older it cools & densers
-Isostacy causes old, dense, thicker lithosphere to sink into asthenosphere > deeper underwater and the result is the oceans go from ‘ — ‘ to ‘U’
-Importance of this is the volume of water a basin can hold, changes sea level along continents

results in:

• massive supercontinents form > reduced sf spreading & oceanic lithosphere gets older & deeper & drags sea levels lower > heavy = sea levels lower
• Broken up continents result in rifting > new oceans with shallow ocean basins which push water higher > lighter = sea levels higher

Question 4

Impacts of the Supercycle on Evolution?

Answer 4

palaeontologists measure the ‘rate of evolution’ by how many new types of living things appear in fossil record at different times

Question 5

The importance of Isolation?

Association with Cambrian Explosion?

Answer 5

• When species broken up into isolated populations in different conditions > natural selection, adaptation, seperate species e.g. Darwins Finches case in Galapagos Islands
• tectonic rifting caused many different, isolated continents which fossil evidence shows great biological diversity at this time in history.
• Also works for ocean species > land masses seperate marine habitats
• Cambrian explosion occurred same time as supercontinent fragmenting