Continental movement
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What is Alfred Wegner’s Theory
• Continents were all once together as a supercontinent: Pangea • the continents have separated since because of continental drift
how many years ago were continents joined together (Pangea) in the Paleozoic era
245 million years ago
What were some observations that Wegner made which supported his theory?
• the continents appear to fit togther like a jigsaw • Fossils of the same prehistoric species were found on different continents that were far apart from one another.
What layers are tectonic plates composed of
• crust & upper mantle
What does the lithosphere consist of? hint* (what layers of Earth)
• crust & upper mantle
The lithosphere floats on a semi-fluid middle mantle that lays below the lithosphere called the??
ASTHENOSPHERE
What are these mainly made up of: - Crust - Asthenosphere - Mantle - Outer core - Inner core
• solid rock and minerals • partially melted • mainly solid • liquid • solid
Forces that can move tectonic plates include:
• convection currents • slab pull • ridge push
What are the types of crust
Oceanic crust and Continental crust
Ocean crust:
• the solid layer of rock on the ocean floor • Thin (approx. 5km) dense due to presence of iron and magnesium
Continental crust:
• Above sea level (continents) • Thickness (approx. 30km) • less dense due to the presence of aluminium and silicon
What is rifting
• convection currents move tectonic plates away from each other (diverge) • the movement creates a rift(gap) in the earths crust • Rifting results in the crust thinning/ cracking/ fracturing
what place has experienced rifting?
Lake Thingvallavatn- Iceland
Hess’s theory fo sea floor spreading
• when rifting occurs underwater the seafloor spreads Rifts are filled with new molten rock which cools, creating oceanic ridges (mountains)
when rifting occurs and the basin is filled with water what may happen?
Water may leak into other water bodies or slowly fill with rain.
what are the three pieces of evidence that support Hess’s theory of seafloor spreading?
• magnetic striping • age of sefloor • sediment thickness
What is magnetic striping?
The patterns of magnetism trapped in rocks on either side of ocean rifts
many rocks contain magnetic iron oixide mineral called?
Magnetite
Does magnetite have a seeking pole?
yes South seeking and north seeking (like a compass)
When molten rock solidifies, all the magnetite lines up with…
Earth’s magnetic field.
The pattern of magnetism is symmetrical:
• the rocks at equal distances on each side of the ridge were formed at the same time • magnetic fields pointing in the same direction
Geomagnetic reversals:
• the magnetic poles have been swapping over long periods of time (thousands to millions of years)