Warm-Up Write a paragraph using these sentence stems: The title of this graphic is... Its purpose is to... One critical observation that I made was... This is important because... I reached a number of conclusions through my analysis of this graphic. First,... Second,... Finally,...
The first step in the scientific method begins with making observations 102 years ago, in 1912, Alfred Wegener made observations about the similarities of different continents Based on his observations, and using the scientific method, he formulated a hypothesis
Alfred s hypothesis Continental Drift Continents once formed a single landmass called pangea The supercontinent, Pangea, began breaking up into smaller continents 250 ma ago The smaller continents drifted into their present locations
Observations and evidence to support his hypothesis Continental Drift 1 The shoreline of the east coast of South America and the shoreline of the west coast of Africa looked like they would fit together like a jigsaw puzzle
2 Fossil evidence The same fossils were found on both continents Mesosaurus 3 Evidence from rock formations The ages and types of rocks matched on both continents Mountain chains that ended on one continent continued on the other
4 Climatic Evidence Continental Drift Debris from glaciers matched across continents Tropical plant fossils were found in areas that are now much colder If continents were joined and in different locations it would explain the climatic differences
.that dude Wegener is Crazy! Tons of evidence supported his theory but.how did the continents move? Wegener said they plowed through the ocean rock check it out Wegener s mechanism for movement was disproved
What happened to crazy Alfred? Wegener died before he could ever prove his hypothesis bummer.
TO BE CONTINUED
Hess-1950
Harry Hess - 1950 Scientist studying a mid-ocean ridge called the Mid- Atlantic ridge What s a mid-ocean ridge? Undersea mountain range with a narrow valley at the center of the ridge called a rift (crack)
Hess proposed a new hypothesis to support Alfred s theory of continental drift Hess said that continents move because of sea-floor spreading that occurs at mid-ocean ridges
Sea-floor spreading Molten magma from Earth s interior rises and weakens the lithosphere creating a rift Magma begins to ooze out of the rift The intrusion of magma pushes the plates apart Magma solidifies to form new oceanic crust Mid-Atlantic Ridge
Hess came up with a great hypothesis. hey if the ocean floor is moving then maybe Alfred wasn t crazy; maybe the continents are moving too! Scientists thought Great now we have two crazy scientists! Hypothesis for sea-floor spreading wasn t accepted because of lack of evidence
Mid-1960 s evidence for Hess s hypothesis was found.paleomagnetism magnetic reversals and sea-floor spreading
Paleomagnetism Earth s outer core is a giant magnet As magma solidifies into rock the magnetic minerals (iron, nickle) align with the magnetic poles Magnetic reversals Magnetic poles change over time as the polarity in the outer core flips Magnetic reversals are recorded in the rock record check it out magnetic reversals
https://www.youtube.com/watch?v=t1- ces1ekto
Hess s hypothesis is supported by the following evidence: 1. Symmetry of magnetic patterns a. Polarity of rocks on either side of the ridge matched 2. Symmetry of ages of rocks Sediment thin by the ridge, thick by the continent Dead critters (fossils) in sediment used to date the rock Radiometric dating (read into your future learning) 3. Patterns were seen on land
Wegener and Hess weren t such crazy dudes after all!!! Mechanism for continental drift = sea floor spreading Mechanism for sea-floor spreading = convection in the asthenosphere