Climate paradox? Geological evidence indicates that Paleozoic glaciations had a wide distribution, ranging from southern South America to India.
Figure 1. Distribution of Paleozoic glaciations.
Introduction to solid Earth
Solid Earth is composed of:
Oceanic and continental crust differ in composition, age, and thickness. Oceanic crust is thinner (5-10 km) and younger than continental crust (30-70 km) and composed largely of basalt. Continental crust is composed mainly of granite.
Figure 2. The solid Earth.
Why do the continents rise above the ocean crust? Continental and oceanic crust are in isostatic equilibrium.
Figure 3. Evolution of a mountain and isostatic equilibrium (from .
Evolution of Plate Tectonic Theory
Direct evidence for plate tectonics:
Figure 4. Reconstruction of Pangaea. Is it just a coincidence that Africa and South America see to fit together like pieces of a puzzle?
Figure 5. World bathymetry (from National Geophysical Data Center). Why are there immense mountain chains and deep trenches on the ocean floor?
Click on the pictures below to see close-up bathymetric maps of trenches and ridges in the ocean (from Virtual Vacationland)
4. Paleomagnetic patterns on ocean floor and ocean crust age. The Earth has a magnetic field, caused by the circulation of liquid iron in Earth's core. Today, because of the magnetic field, compasses point to the north. However, in the past, the magnetic field has reversed so that a compass would have pointed to the south. Basalts act as paleo-compasses. Iron-rich components within the basalt align with the magnetic field.
Figure 6. Map of the ocean floor magnetism. Notice the symmetry of the magnetic pattern in the Atlantic Ocean. What does this mean?
Plate tectonic settings
Figure 7. Modern plate tectonic map.
Figure 8. Mantle convection.
Divergent plate boundaries
example: mid-Atlantic Ridge
Figure 9. Evolution of an ocean basin.
Convergent plate boundaries
1. Continent-ocean collision- example: Nazca and South
American Plates (Andes)
Figure 10. Sketch of a convergent plate boundary.
Transform plate boundaries
Example: Pacific and North
American plates. The
Pacific Plate is moving northward relative to the North American Plate.
The San Andreas Fault marks the junction between these plates. In 50 million
years, western California will encounter the Aleutian Trench!
Figure 11. Putting it all together. Sketch of the tectonic settings in an ocean basin (e.g., the Pacific Ocean).
Figure 12. The Earth's major mountain chains. What do these mountain chains indicate about the Earth's tectonic past?
Plate tectonics and climate
View a quicktime movie of continental drift through geological time.
How does plate tectonics influence climate?
BLAG hypothesis: Plate tectonics influence
global climate by moderating atmospheric CO2 concentrations
Uplift weathering hypothesis: Uplift accelerates chemical weathering, drawing down CO2, and cooling the global climate.