Plate Tectonics and Climate

GEOL 1130

The Chicken or the Egg

• Volcanic CO2 and chemical weathering function as Earth’s thermostat– Is there one leading the change and the other

reacting?– Is there some other factor that governs the

long-term swings in Earth’s climate?

• Let’s look at last 550 million years of Earth’s history to test several hypotheses

Effects of latitudinal position of continents? Polar Position

Hypothesis

Activity: Put Polar Position Hypothesis in words!

Modeling Pangea: Boundary Conditions?

Modeling Pangea: Output suggests interior aridity

Modeling Pangea: Model results vs. geologic data

Modeling Pangea: Output suggests extreme seasonality

Modeling Pangea: Output suggests monsoons important

Back to Chicken or Egg

• In thermostat, two possible factors that could be in drivers seat:– Plate tectonics– Weathering

• Two competing hypotheses– BLAG (named after authors) or Spreading Rate– Uplift-Weathering

• Activity: write out negative feedback loop that starts with spreading rate change and incorporates Earth’s thermostat as check

Spreading Rate Hypothesis in words?

Sources of CO2

Does the last 550

million

years of geologic

history contain the

record we need to test

this hypothesis?

Activity: Which time periods show the fastest and slowest rates ofspreading, respectively?

Uplift-Weathering Hypothesis

• Exposure of fresh rock due to uplift causes draw down of CO2 through chemical weathering– Climate cools

• Fresh rock surfaces diminish if uplift diminishes and CO2 builds up– Climate warms

Uplifted areas have greater chemical (and physical) weathering

Activity:

Write out a negative feedback involving the uplift weathering hypothesis