The not so rigid Earth

Continental Drift = Hypothesis that continents had once been one or more lager land masses that had separated and moved apart

1911 = Alfred Wergener (Meteorologist) believed that world climates were much different;

also stated that land bridges had once connected the major continents;

His proof of evidence;

* similar fossils

· rock structures

· ancient climates

Wergener named his "super continent" Pangaea which means "all earth"

Fossil Evidence

Many scientist ignored Wergener's proposal

Evidence in support of continental drift in the form of fossil evidence started to be found.

Lystosaurus remains have been found in South Africa, and Antarctica

· this was an animal that lived around swamps and rivers

Glossopteris was a fern that had been found in Africa, Australia, India, and Antarctica

· Skeptics proposed a land bridge, but now remnants below sea level remain

Deposit Evidence

Glacial deposits and effects of deposits and movement have been found across 5 continents

Salt beds were also deposited in what is now Texas and Germany

These deposits only occur in arid (dry/hot) regions which are usually equatorial

Magnetic Clues

Polar Wandering with evidence of paleomagnetism

Some rocks contain Iron bearing minerals that become magnetized when forming

These grains line up pointing toward the magnetism south and north

When looking at ancient rock, scientist noted that according to the line up of grains, the magnetic pole seemed to wander hence the term "polar wandering"

Since it is almost impossible for more than our present poles to exist, by piecing the continents together, grains would point to 1 pole, very close to our present day pole

Seafloor Information

After many years of research, scientist have been able to determine that the sea floor is made up of bands of rocks

the youngest rocks are at the mid ocean ridge

the oldest rock is on either side and as they spread out they become increasingly older

scientist have found no sea floor deposits older than 200 million years, but continental rock has been dated almost 4 billion years

Scientist have also found alternating bands of magnetism on the sea floor

Basaltic rock, a rock that fan hold a weak magnetic charge showed varied bands

These bands reflected geologic shifts in Earth's history

Volcanic activity associated with divergent boundaries may occur

as blocks of crust pull away, it sinks and on continental areas, Rift Valleys form

Transform faults are boundaries at which plates move past each other in opposite directions, but at different rates

San Andreas Fault is a Transform Fault

Convergent Boundaries are boundaries between two colliding plates (Earthquakes are common in these areas)

When 2 oceanic plates collide, the edge of one is bent downward

as it descends into the asthenosphere, it melts

the region where it bends downward is the Subduction Zone

A deep sea trench is formed on the ocean floor at the point of subduction

Eventually the plates that carry the continents collide and the continents will meet

Continental rocks have low density so they do not sink to the ashenosphere but buckle and rise

"Himalyas"

Earthquakes

Shallow focus Earthquakes are produced at the outer edges of trenches where plates are bent downward and scrape against the top plate

these develop when rocks are folded into mountains

they develop as plates move past each other in transform faults and Mid ocean ridges

Deep Focus Earthquakes occur as the plates is subducted deeper into the mantle

1. They only occur in the descending plate