Presentation on theme: "Alfred Wegener 1912 Proposed idea (hypothesis) of “CONTINENTAL DRIFT”"— Presentation transcript:
Alfred Wegener 1912 Proposed idea (hypothesis) of “CONTINENTAL DRIFT”
Evidence for Wegener’s Idea Continents fit together like puzzle pieces
Fossils found on different continents were identical…separated by thousands of miles…how’dey do dat? Evidence for Wegener’s Idea
This is a freshwater reptile called a Mesosaurus. Look at the distribution of fossils….hmmmm Wegener compiled information about fossil discoveries from around the world. He felt this evidence was compelling.
Assorted Fossil Evidence
Continents fit together like puzzle pieces Fossils found on different continents were identical…separated by thousands of miles…how’dey do dat? Dey ustabe neighbors Evidence for Wegener’s Idea
Continents fit together like puzzle pieces Fossils found on different continents were identical…separated by thousands of miles Evidence from Glaciers: Marks in bedrock left behind by glaciers located on AFRICA, SOUTH AMERICA, INDIA, and AUSTRALIA indicate that portions of these continents must have been CONNECTED in polar regions far from their present positions. Evidence for Wegener’s Idea
Marks from ice movement striations
Evidence for Wegener’s Idea Rock types on the east coast of North America MATCH EXACTLY the rocks in the British Isles, Scandinavia, and Africa
Continental Drift Hypothesis Hypothesis The continents were all connected at one time Supercontinent was called Pangaea Pangaea broke apart Pangaea broke apart up into two continents call Laurasia and Gondwanaland Continents are still moving today
Few believed Wegener….. …because he could not explain what hidden mechanism might be responsible for the movement of an entire continent!!! …plus, he was “only” a climatologist
1930 Wegener leaves for Greenland to seek more evidence to test his hypothesis. He is never seen again. Some speculate that he ate his own dogs before he froze to death. The last photo him… His hypothesis is “hotly” debated for the next 30 years
Cut and Paste Playtime
Plate Tectonics “What Wegener Wished He Knew” (animations from USGS) A.K.A.
Evidence for Plate Tectonics 1. Location of earthquakes and volcanoes
Map of earthquake foci for the last 30 days
Evidence for plate tectonics So, how would you characterize the distribution of earthquakes and volcanoes around the world? Random?Patterned? Isolated?
Evidence for plate tectonics 1. Location of earthquakes and volcanoes The distribution of earthquakes and volcanoes is not random. Earthquakes and Volcanoes occur TOGETHER in narrow bands under the oceans and along the edges of some continents.
Evidence for plate tectonics …turns out…these locations are the edges of plates called “Plate Boundaries” where the plates rub against each other.
Volcanoes Volcanoes are evidence of HEAT escaping from inside the Earth This HEAT leaves the Earth as hot LAVA So…if heat from inside the Earth is making it all the way to the surface…MAYBE this movement of heat can move continents too
What Makes the Plates Move? A concept in Science that Wegener KNEW, but did not imagine it could move continents. 1. The plates move due to the transfer of HEAT energy from the Earth’s core 2. Heat leftover from Earth’s formation and produced by radioactive decay creates DENSITY differences in the mantle. 3. This causes the fluid mantle to flow. 4. The flow of mantle material pulls on the crust above it…like a leaf on a stream
Complete the Demo Analysis Sheet
The of Plate Tectonics Evidence: Convection currents in the mantle move the plates aroundConvection currents in the mantle move the plates around…and have been doing so for more than 4 billion years (1:10) Convection currents in the mantle move the plates around Convection cell movement causes plates to collide, rip apart, and plunge back into the mantle THEORY
We’re not sure which model is correct. This current model (A) predicts that convection cells are limited to the outermost plastic mantle. This current model (B) predicts that convection cells extend through the mantle toward the Lehmann discontinuity. Don’t you just LOVE the uncertainty of Science?
Which model has the New York State Ed Dept selected for you?
Current Scientific Theory “Plate Tectonics” 1. The Earth’s crust is composed of about 22 plates 2. The plates are rigid and may contain CONTINENTAL or OCEANIC crust, or BOTH 3. CONTINENTAL CRUST is mostly Granite 4. OCEANIC CRUST is mostly Basalt
The Plates…IN COLOR
Evidence cont’d 2. Age of seafloor Oceanic igneous rock is much younger than continental igneous rocks Oceanic rock gets younger as you approach the mid-ocean ridge (mountain range which runs through all world’s oceans)
Map showing Ages of oceanic crust
Reading Passage Please open your text book to page 337 and read the passage titled “Seafloor Spreading” to the end of 339
Magnetic pattern in rocks –Earth’s magnetic pole reverses Earth’s magnetic pole reversesEarth’s magnetic pole reverses –Magnetic crystals line up with earth’s poles when the magma hardens –Patterns in ocean rocks show parallel strips on either side of the ridge that match in width, age, distance from the ridge, and magnetic polarity
Hugo Benioff suggested that this Earthquake pattern shows a plate subducting (sinking) into the mantle (1940s discovery)Earthquake pattern
Continent-continent collision (Subduction has endedContinent-continent collision (Subduction has ended)
1963 Tuzo Wilson Developed the hypothesis of hot spots to explain islands like Hawaii & a third kind of plate boundary called a transform plate boundary
Transform Boundary Plates slide past one another –Ex. San Andreas fault Crust is neither created nor destroyed
Hot Spots Places where magma reaches earth’s surface Typically not associated with plate boundary As plate moves over hot spot, island chains form As plate moves over hot spot, island chains form Example: Hawaii Hawaii
So by the mid-60’s all the evidence came together to form the Theory of Plate tectonics This theory states that the Earth crust is broken into a series of plates which are constantly on the move.
Convection computer model. The most current understanding.