Plate Tectonics, Life and Climate

Question 1

Earth’s structure

Answer 1

Continental crust is 30 to 70 km thick,
composed of granite and low in
density.
Ocean crust is 5 to 10 km thick,
mostly basalt and higher in density.
Below these layers lie the mantle that
extends 2890 km into the interior and
is of high-density and composed of Fe
and Mg.
Over millions of years, the
asthenosphere behaves like a viscous
fluid.
Plates move 2 to 10 cm a year.

Question 2

Tectonic plates

Answer 2

Tectonic plates are pieces of Earth’s crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from silicon and aluminium).

Question 3

Convergent and divergent margins

Answer 3

A divergent boundary occurs when two tectonic plates move away from each other. Along these boundaries, earthquakes are common and magma (molten rock) rises from the Earth’s mantle to the surface, solidifying to create new oceanic crust. The Mid-Atlantic Ridge is an example of divergent plate boundaries.

Question 4

Earth history in 5 minutes

Answer 4

5 minute mark Earth formation
4 min 46 seconds Water on Earth
4 min 7 seconds Unicellular life on Earth + Faint
Young Sun
2 min 43 sec (half history) First multi-cellular life
42 seconds (when we start to
know something about climate)
Snow-ball Earth (some life
survived glaciation)
35 seconds Mollusks, fish
23.5 seconds Large trees (coal)
4.3 seconds Dinosaurs
0.2 seconds Beginning of modern man
0.002 seconds Last 100 years

Question 5

Continent distribution through geologic time

Answer 5

Distribution of continents on Mollweide equal area projection
Present-day Earth (left) and Proterozoic 560 Ma (right)
Multi-cellular life found in the Pre-Cambrian era

Question 6

Paleozoic

Answer 6

Ordovician (left) 450 Ma minor glaciations
Devonian (right) - Fish appeared in oceans

Question 7

Late Paleozoic

Answer 7

Carboniferous (left) 300 Ma - rise of land plants and large
trees. Oxygen rich atmos.
Late Permian (right) 260 Ma - start of amphibians
Mass extinction at the end of the Permian (50% of animal life
& 90% of marine species)

Question 8

Mesozoic

Answer 8

Final assembly of Pangea before break-up at 220 Ma (left) in
the Triassic
Cretaceous (right) 120 Ma. Dinosaurs evolved from reptiles.
Crocodiles at high latitudes. Warmest period of the
Phanerozoic.

Question 9

Cretaceous-Tertiary extinction

Answer 9

Strong evidence that a large meteorite or comet collided with Earth 65 Ma.
Shock would heat atmosphere in vicinity and produce large amounts of Nitrous
oxides => leads to ozone loss in stratosphere. Nitrous oxides leave
atmosphere as highly acidic rains.
Impact of projectile and penetration in Earth’s crust throws fine particles high in
the atmosphere and even in low orbit where they could persist for months =>
block sunlight for photosynthesis => plants become extinct. Also cooling of
surface after initial heat dissipated.

Question 10

Early Cenozoic

Answer 10

Cenozoic: 50 Ma Eocene (left); 35 Ma Oligocene (right)
KT boundary identified in sedimentary layers by well defined clay deposits with
high amounts of iridium. Earth impact by a meteor caused 75% of species to
become extinct.
All these effects: shock heating, fires, acid rain, ozone loss, dark and cold for
several months to years - is too stressful for species and may have been the cause
of rapid extinctions.

Question 11

Late Cenozoic

Answer 11

35 Ma (left) Oligocene. Opening of Drake passage between South
America and Antarctica.
Formation of Antarctic circum-polar current.
Antarctica started to cool further and build ice mass.
20 Ma (right) Miocene - rise of the Tibetan plateau and the Himalayas

Question 12

Late Cretaceous

Answer 12

90 Ma (left) - first stage of Rocky Mountains
65 Ma (right) - first large mammals
4x present CO2 levels due to increased volcanisms
Notice migration of the Indian sub-continent