Plate Tectonics and Climate Change

Geologic Time Scale and the evolution of the Planet Earth

Climate Paradox

1.Today Large Glaciers are found only near the poles

2. Reef are found only near the equator

3. Large deserts are found at around 30o latitude

Ancient glacial deposits of similear age spread around the world (A).

How could glaciers exist in all these areas,particularly near the poles?

1. The places where glacial deposits are found must have been near the poles at the time the glacier existed.

2. Places where glacial deposits are found must have once been much closer together (B).

How do explain the more logical possibility that the continents must have been joined together and subsequently moved to their respective positions?

Plate Tectonic Theory

Begin by looking at where mountain belts are found

Mountain belts tend to be found along the margins of continents or where two continents meet such as India and Asia.

The continents can be thought of descete plates

The continents are also separated by plates. The plates that are between the continents are called Oceanic Plates.

There are, therefore, 1) Continental Plates and 2) Oceanic Plates covering the globe.

How do plates form?

Remember the characteristic layers of the Earth's interior

The semi-molten mantle is the layer on which the continents ride.

Convection of Mantle material

Divergence

caused by mantle convection brings material to the surface and

produces new ocean crust

Convergence

Oceanic crust (more dense) subsides beneath continental plate (less dense) and causes mountains to form on the continental crust along the contact between the two plates

Divergence and Convergence are going on constantly

The rate of sea floor spreading is on the order of millimeters to centimenters per year

It takes millions of years for plates to move far apart and for large oceans like the Atlantic to form

California-Washington Margin-MOVIE

The Evolution of the Continents over the past 280 million Years

The movement of the the continents has many effects including:

1. Providing or destroying land bridges used by organisms (including plants) to migrate from one continent to the other

2. Opening or closing ocean gateways which affects the oceanic currents--where they flow

3. Produces land barriers such as large mountain belts that affect weather patterns such as the Himalayas

4. Affects weathering of minerals which influences the chemistry of the oceans and the atmosphere and ultimately affects climate.

5. Changes the land to sea ratio which affects Earth's albedo

6. Can put continents at latitudes near the poles and thereby contribute to glaciations

Generally, these tectonic changes take a long time (millions of years). But the climate of any of the Geologic epochs was strongly dependent upon the configuration of the plates, just as our present plate configuration affects modern climate.