Earth in Motion

• Principle of Uniformitarianism:

• Processes observable and measurable today have created all the geological features, over long periods of time.

Why are continents high and oceans deep?

Why do continents across the Atlantic fit together like a jigsaw puzzle?

Why were fossils similar in the past on continents that are now separated?

How are mountains made and why do they occur where they do?

Alfred Wegener

Geographic Fit ofGeographic Fit ofthe Continentsthe Continents

One of the first piecesOne of the first piecesof evidence used toof evidence used to

argue forargue forcontinentalcontinental

driftdrift

Suggested that all continents Suggested that all continents were once together in a single were once together in a single supercontinent called Pangeasupercontinent called PangeaFig. 2.1

Geology and Paleontology Matches Geology and Paleontology Matches on Opposite Sides of the Atlanticon Opposite Sides of the Atlantic

Fig. 2.2

Wegener’s Pangaea

Wegener’s Dilemma

What is missing from this picture?

Challenger Expedition

Challenger Expedition

• What’s down there?– The dredge

Early Oceanographers

Challenger Expedition

• Determining Ocean Depth

Wyville-Thompson’s Frontspiece

Research Vessel Vema

Coring on the Vema, 1960’s

Vema Depth Record

Earth’s Magnetic Field

The Seafloor as a MagneticTape Recorder

• During and after WWII, it was noticed that the magnetic field near the ocean floor exhibited significant variation.

• Subsequent analysis shows that the changes in the rocks reflect changes in the Earth’s magnetic field over time.

Fig. 2.11

Magnetic Reversals in a Magnetic Reversals in a Single VolcanoSingle Volcano

Fig. 2.11

The Magnetic RecordThe Magnetic Record

Fig. 2.11

Magnetic Reversals at Mid-ocean RidgesMagnetic Reversals at Mid-ocean Ridges

Fig. 2.11

Figure 10-08

Plate Tectonics

Theory of Plate Tectonics

• Surface of the Earth is covered by a series of plates

• Creation of seafloor occurs at mid-ocean ridges, where volcanism creates the seafloor.

• Consumption of the seafloor occurs at convergent margins, where plates are subducted back into the mantle.

• Continents never subduct; they are passengers riding on the plates

Plates of the Earth’s crust

Howocean basinsformed

Plates

• Group of rocks all moving in the same direction

• Can have both oceanic and continental crust or just one kind.

Three Types of Plate BoundariesThree Types of Plate Boundaries

Fig. 2.5

Transform Divergent Convergent

Transform Boundaries

The San Andreas Fault

Transform Plate BoundaryTransform Plate Boundary

Fig. 2.10