Continental Drift Historical Theories 1596-Abraham Ortelius (April 14, 1527 – June 28, 1598) was a Flemish cartographer (map maker) and geographer. Ortelius is believed to be the first person to imagine that the continents were joined together before drifting to their present positions. Based on the similarities in the coast lines of Americal & Africa, Ortelius thought that the continents have moved
WEGENERS CONTINENTAL DRIFT During early 1900’s Alfred Wegener independently proposed the hypothesis that continents were once joined together in a single large land mass he called Pangaea (meaning “all land” in Greek).
He proposed that Pangaea had split apart and the continents had moved gradually to their present positions -
200 million years ago: Pangaea broke up. southern portion of Pangaea Gondwana, and the northern portion Laurasia.
About 70 million years ago: Atlantic Ocean opened. India’s collision with Eurasia would form the Himalayan Mountains.
The position of the continents today. The continents are still moving at very slow rate.
Evidence for Continental Drift
• Similarity in Coastline • Fossils • Orogenic belts • Glaciation
Continental Drift : Geographic Fit Continents seem to fit together like pieces of a puzzle
Continental Drift: Fossils
Similar distribution of fossils such as the Mesosaurus
Continental Drift: Mountains
Mountain ranges match across oceans Continental Drift: Glaciation
Glacial ages and climate evidence
Continental Drift Not Accepted!! • Why didn’t people believe in continental drift? • People couldn’t imagine the antiquity of the earth. • People couldn’t imagine the force to move the continents • Wind and currents could possibly move fossils • Theory was not accepted by scientists
Wegener's problem He could not find the force that was causing the continents to drift. Because of this, he could not convince anyone that continents could move. He died in Greenland on an expedition. At the time of his death, no one believed his hypothesis! But….Technology developed during the 1940’s changed all that!
Seafloor Spreading • 1960’s: Henry Hess discovered that Seafloor is spreading which supports Wegner. • Using new technology, radar, he discovered that the seafloor has both trenches and mid-ocean ridges.
Hess proposed that new crust is being generated at the mid-ocean ridges. * This newly generated crust , flows sideways, in both the directions, away from the ridge.
Picture from http://library.thinkquest.org/17457/platetectonics/4.php
. This explained how the crust could move—which the continental drift hypothesis could not explain. Evidence for Spreading * In 1968, scientists aboard the research ship Glomar Challenger began gathering information about the rocks on the seafloor. * Scientists found that the youngest rocks are located at the mid-ocean ridges.
Mechanism for Plate Tectonics • Seafloor Spreading provided insight to the mechanism for how the continents moved. • The magma which pushes up at the mid-ocean ridge provides the new land pushing the plates, and the subduction zones gobble up the land on the other side of the plates.
Plate Tectonic Theory
* The combinations of Hess’s Sea Floor Spreading and Wegener’s Continental Drift hypothesis is Theory of plate tectonics: • The Earth’s crust and part of the upper mantle are broken into sections, called plates which move on a plastic-like layer of the mantle
Tectonic plates move.
Three types of plate boundaries * Divergent
• Also known as seafloor spreading • Plates are separating from each other as a new land mass forms • This is seen at mid-ocean ridges and rifts • Plate separation is a slow process. For example, divergence along the Mid Atlantic ridge causes the Atlantic Ocean to widen at only about 2 centimeters per year.
* Convergent
* Two continental plates collide & crumple the edges of the plates & form mountains. * We can see the end result of the collision between the Indian & Eurasian plates which are the Himalayan Mountains.
* Transform