Presentation on theme: "Wegener’s Continental Drift Hypothesis States that the continents once formed a single landmass, broke up, and drifted to their present locations. His."— Presentation transcript:
Wegener’s Continental Drift Hypothesis States that the continents once formed a single landmass, broke up, and drifted to their present locations. His evidence includes: –Shape of the continents –Fossil evidence –Similar rocks
The shape of some of the continents look like they could fit together like …
Fossil Evidence Fossils of the same species are found on two different continents.
Rock type and structure correlation
Wegener had a lot of evidence…
He could not satisfactorily explain the forces moving the continents. Scientists could not explain how the continents were moving. Flaws in Wegener’s data had the continents moving much to far and too fast. …so why was his hypothesis almost universally rejected?
The large land mass was called Pangaea. Pangaea
Continental Drift - animation
Mid-Ocean Ridges and Sea-Floor Spreading Mid-ocean ridges are places where sea-floor spreading takes place.
Mid-Ocean Ridges and Sea-Floor Spreading As the tectonic plates move away from each other, the sea floor spreads apart and magma fills the gap.
As the new crust forms, the older crust gets pushed away from the mid-ocean ridge. This means that the older crust is farther away from the mid-ocean ridge than the younger crust is.
Evidence for Sea-Floor Spreading: Magnetic Reversals Throughout Earth’s history, the north and south magnetic poles have changed places many times.
Magnetic Reversal of Earth’s Poles
Magnetic Reversals and Sea-Floor Spreading The molten rock at the mid-ocean ridges contains tiny grains of magnetic minerals like iron. These minerals align with the magnetic field of the Earth while liquid, then when they cool and harden, they make a record of the magnetic poles. This record is then carried slowly away from the spreading center of the ridge as sea-floor spreading occurs.