Presentation on theme: "Contracting Earth Theory"— Presentation transcript:
1 Contracting Earth Theory The molten Earth cools and contractsThe crust wrinkles and crumplesMountains formWhat are some problems with this hypothesis?What observations do you know of that may contradict this idea?
2 The Expanding Earth 20th century - radioactive decay Land masses are ripped apartExplains the continentsWhat are some problems with this hypothesis?What observations do you know of that may contradict this idea?
3 Discussion Questions1. How did Wegner’s Hypothesis challenge the “contracting Earth model”?2. How does the distribution of ages of the ocean floor support “Continental Drift” and challenge the “expanding Earth model”?
5 Continental Drift Proposed by Alfred Wegner in 1915 Continents are a giant jigsaw puzzlePut together get Pangea (“all land”) a supercontinent
6 Evidence for Continental Drift Jigsaw Pattern FitUsing the Continental Shelves continents fit nicelyContinents began breakup 200 million years ago
7 Evidence Cont. Fossils Mesosaurus Fresh water reptile Could swim, but not an oceanFound in South America and Africa
8 Evidence Cont. Fossils Lystrosaurus Cynognathus Land dwelling reptile Could not swimFound in Africa, India, and AntarcticaCynognathusFound in Africa, South America.
9 Evidence Cont. Fossils Glossopteris Fern Habitation area dictated by ability of plant to spread.Seeds to big to be transported by wind.Found in Africa, India, South America, Australia, and Antarctica.
10 Evidence Cont.RocksSimilar composition, age, and geologic structures on both sides of the AtlanticWhen continents are together have continuous pattern
11 Evidence Cont. Mountains See continuation of mountains on both sides of Atlantic OceanNorth America and Europe together have a continuous mountain chain, rock is similar composition and age
12 Evidence Cont. Paleoclimatic Data Evidence of Tropical Climates in non tropical areas.Evidence of Low-latitude deserts in non desert areas.Evidence of Glaciers in areas of tropical climates today.
15 Question for Wegner What is the mechanism of the movement? Wegner proposed that the tidal influence of the moon was strong enough to move continents.Continents plowed through ocean crust.
16 Refining a Hypothesis Paleomagnetism Earth has a magnetic field creating a north and south pole – similar to a small magnet.Magnetic Field has reversed over Earth’s history.
17 Magnetic SignatureIron-rich (ferromagnesium) minerals become weakly magnetized in the direction parallel to the existing magnetic field as they cool below 580 oC.The rock retains the signature unless heated up past 580 oC.If the rock moves or if the magnetic pole changes, the rock retains the original magnetic signature.
18 Polar WanderingStudy of lava flows showed that magnetic signature of lava flows of different ages varied widely.
19 Magnetic signatures indicate that the magnetic poles have moved. Taken separately with no continental movement, the data indicate different pathways for the pole movement.If continental movement is incorporated, the polar wandering for the different continents are identical.
20 Magnetic Reversals and Ocean Floor Data Earth’s Magnetic field has reversedIn addition to magnetic signature, polarity is recorded in rocks [either normal (present day) or reversed].At mid-ocean ridges, new oceanic crust (basalt – mafic composition) is generated and records the magnetic signature and polarity.