Evidence of continental drift

- theory that explains continental drift – plate tectonics

- theory developed in the 60’s by geophysicists

- "When the plates move, the continents and ocean floor above them move as well.

   Continential Drift occurs when the continents change position in relation to each other."

- 1912 Alfred Wegener and Frank Taylor – proposed theory that roughly 100-300

  million yrs ago, Earth had only one giant continent which soon after began breaking up into

  today’s six continents – Africa, Eurasia, Australia, N & S America, and Antarctica –Pangaea

  (all lands)

- Fit of the continents

- Matching of floral/fauna fossils on distant continents – identical fossil species along coastal

  parts of Africa and S. America

- Matching of broad belts of sedimentary rock match on Africa and S. American coasts as well

  as New Zealand and California.

- Wegener was aware that a continental ice sheet covered parts of South America, southern

  Africa, India, and southern Australia about 300 million years ago. Glacial striations on rocks

  show that glaciers moved from Africa toward the Atlantic Ocean and from the Atlantic

  Ocean onto South America. Such glaciation is most likely if the Atlantic Ocean were missing

  and the continents joined at one point in time.

- The positions do not match: If the continents were cold enough so that ice covered the

  southern continents, why is no evidence found for age-old ice in the northern continents?

  The answer for this is that the present northern continents were at the equator at 300

  million years ago. The discovery of fossils of tropical plants (in the form of coal

  deposits) in Antarctica led to the conclusion that this continent previously must have

  been situated closer to the equator, in a more temperate climate where more tropical

  vegetation could grow.

- For visual evidence, today scientists use satellites, both visible and infrareds to view

  fault/plate activity by observing broad rock formations at faul-lines as this picture of the

  Zagros mountains in southern Iran where the Arabian plate is impacting the Iranian plate.

Evidence of the K-T Mass Extinction

- "Cretaceous-Tertiary" (KT)

- Since Luis Alvarez first proposed a layer of iridium as evidence of a giant asteroid crashing

  into the Earth, further studies have supported his ideas. Tiny crystals of quartz were found

  at the Cretaceous-Tertiary boundary with a pattern of cracks, a 'fracture pattern', of the

  type which would have been formed by the huge pressure wave resulting from an asteroid

  impact. Tiny beads of glass like quartz, which would only be formed under conditions of

  extreme heat and pressure consistent with an impact, were also found at the Cretaceous-

  Tertiary boundary.

-The most persuasive evidence for an asteroid impact would of course be the crater it

 produced, but for many years this could not be found - despite several suggested sites.

 Alvarez and his colleagues had calculated that the asteroid would have to be about

 10 km across, so it would have to be a big crater - more than 150 km across. then, in

 1981, a huge crater off the Yucatan peninsula of Mexico, which had originally been thought

 to have had a volcanic origin, was put forward as a possibility. Research on this crater,

 named after the nearby village of Chicxulub, has since shown that it is indeed the result of

 an extra-terrestrial impact which probably took place some 65 million years ago at the end

 of the Cretaceous.