Internal Energy and Continental Drift

Question 1

What are the sources of Earth’s ‘internal heat’?

Answer 1

Residual heat from gravitational contraction & asteroid impacts
Active source: radioactive decay of unstable isotopes

Question 2

How Hot is the Earth?

Answer 2

Surface: Near 0°C
Under tectonic plates (~100 km depth): ~1300°C
Base of mantle (2900 km depth): ~3500°C
Core: 6000°C

Question 3

How do we know how hot the earth is?

Answer 3

1. Experiments (to find the temp. needed to melt iron in the core)
2. Measurements of heat flow (from Earth’s surface)
   - Use drill holes into rock, or probes into sediment
   - Measure temperature increase with depth (~2-3°C/100 m in crust)
   - Multiply by thermal conductivity of rocks -> heat flow

(Total global heat flow per year is equivalent to: 100 times energy released from earthquakes per year or ~ 3 times human energy consumption per year)

Question 4

What does Earth do with its internal energy?

Answer 4

temp. differences -> heat flows by conduction, convection
convection in liquid outer core -> earths magnetic field
convection in mantle -> plate tectonics -> creates topography

Question 5

what are plate tectonics driven by? what do they create?

Answer 5

earth’s internal heat engine

surface features on the earth

Question 6

what is the theory of plate tectonics?

Answer 6

Seafloor spreading
Rock magnetism
Types of plate boundaries

Question 7

Earth has:

Answer 7

Continents (solid rock) above water
Mountain chains on continents
Seafloor ridges below ocean water
A distribution of earthquakes and volcanoes that is not random, but lines up in patterns with some topographic feature

Question 8

Whose 1858 map noted that Africa and S.America ‘fit’?

Answer 8

Pellegrini’s

Question 9

Who proposed continental drift?

Answer 9

Alfred Wegener 1912

Question 10

what is the evidence for Continental Drift?

Answer 10

1. Fit of continents
2. Fossils (Identical fossils preserved in sedimentary rocks on continents separated by wide oceans
   - Reptiles, worms, insects: some could not have swum
   - Fern seeds: too large to have been wind blow)
3. Mountain Belts (Mountain belts of specific age and structure end at continent edges but continue at opposing edge on other continents (e.g. Cape Fold belt, Appalachians))
4. Glacial Evidence (Glacial striae on rock surfaces (pebble scratches) are evidence of ice flow direction, Glaciers (ice) move over surface and leave distinct deposits and striae, Continents with glacial deposits sit at equator today, If continents were once together, then a nice fit at South Pole)
5. ‘Paleoclimatic belts’ (Certain rock types form at specific latitudes, Coral Reefs (Limestones) form in tropical seas, Coal forms at warm swamps in the tropics, Glacial deposits occur at high latitudes).

Question 11

Before 1960’s there were multiple lines of evidence but Continental Drift was refuted. Why?

Answer 11

Wegener (& other believers) referred to as ‘drifters’, overly zealous
Failed to explain what forcesand mechanisms would move the continents
Little change in opinions until 1940-50’s - exploration of the sea floor