Continental Drift

Plate tectonics

(video in the library notes on video in binder)

• A. HISTORY AND THEORY• Proposed by geologist Alfred Wegener

1912 initially incorrect explanation but the modified theory is widely accepted

• (seafloor stationary and the continents move WRONG)

see text diagram (pgs. 11-12)

• 10 major plates and many minor plates up to 100 km thick Continents ride (less dense material) on the moving crustal plates

• These are the possible events at the boundary between the plates

Seafloor Features: Deep Ocean• Plate Boundaries

– Ridges (Rises), Trenches, Transform Faults, Fracture Zones

These are the possible events at the boundary between the plates

1. slide 2. spread 3 subduction

These are the possible events at the boundary between the plates

4 subduction w/ continents

4a later subduction w/ continents

B. EVIDENCE OF DRIFT

• 1. OLD a. puzzle pieces• b. fossil distribution• c. sedimentary layers • "Gandwanan Sequence" similar geology

on 4 southern hemisphere continents• sand stone with coals• black shale• glacial till

2. NEW evidence (POST WW II)

a. earthquake • shallow quakes at ridges and boundaries• shallow and deep quakes at trenches• distribution "Ring of Fire“

b. movement can be measured from space

• c. magnetics- paleomagnetism• magnetic reversals of earth's magnetic

field show a chronology• draw an example of the Mid Atlantic Ridge•

C. BIOLOGICAL CONSEQUENCES of continental drift

• 1.Vent Communities• Fissures at plate boundaries, super

heated water spews minerals, gases onto the ocean floor. May exist for several hundred years (NO LIGHT) Energy rich chemical begin the food chain. ? How do animals in the community find the next vent that may be hundreds of miles away?

VI. SEA LEVEL CHANGES fig. 1-11

• A. EVIDENCE• The EVIDENCE terrestrial sediments

have been observed in marine environments

• Evidence of sea level drop 15,000 years ago down 120m (400 ft)

• Extends land to the continental shelf•

B. IMPACT ON THE BAHAMAS

• Paleoprovidence (handout)• Bahamas "baja mar" shallow sea 700

islands, cays, and rocks• 5,380 sq. miles • 50 miles from US mainland

• 1. sea level changes the growth pattern of coral

• islands are made of limestone deposited by coral arragonite)

• The sea may have been higher or the land uplifted

• 2. Biologically this is significant. decreases migration and dispersal distances between land masses. Unites separate islands.

• 3. Tongue of the Ocean 10,000 ft. valley