Download 1-2 Notes: Continental Drift Continents Join Together and Split Apart

1-2 Notes: Continental Drift
Continents Join Together and Split Apart
 In the ___________’s, mapmakers noticed that the coasts of Africa and South America looked like fit together like
puzzle pieces.
 In ___________, Alfred Wegener proposed a hypothesis called continental drift.
 His hypothesis stated that Earth’s landmasses were once joined together in a single continent and have gradually
drifted _________________.
 This idea was not accepted until the mid-1900’s.
Evidence for Continental Drift
 Extraordinary claims require extraordinary evidence!
 What evidence is there for continental drift?
 There are ____ main kinds of evidence for continental drift: fossils,
climate, and geology.
Fossils
 Mesosaurus is an ancient reptile whose fossils are found ONLY in
South America and Western _____________________.
 There are many other fossils found around the world that support
the theory of continental drift.
Climate
 Greenland is an island near the Arctic circle that is covered in ice.
 BUT…Fossils of ____________________ plants can be found on the shores of Greenland.
 How???
 Greenland was probably closer to the _______________________ in the past.
 South Africa has a warm climate, but its rocks have deep scratches clearly made by _____________________.
 South Africa once existed much closer to the _________________________________.
Geology
 The types of rock found in Brazil perfectly match rock found in western Africa.
 Limestone layers in the eastern U.S. match limestone layers found in Scotland.
Pangaea and Continental Drift
 The continents were once joined in a huge supercontinent called Pangaea.
 The word Pangaea comes from the Greek for “_________ lands.”
 When Wegener developed his hypothesis, he could not explain __________ the
continents moved.
 Because of this, people disregarded his idea at first.
 The theory of plate ___________________ built on Wegener’s ideas but also
explained HOW plates and their continents move.
Evidence from the Sea Floor
 When ______________________ technology was invented, scientists began mapping the dips and bumps in the
ocean floor in the 1950’s.
 They expected it to be mostly smooth and level, like a flat underwater ____________________.
 What scientists found instead were huge underwater mountain ranges called mid-ocean ridges.
Sea-Floor Spreading
 Mid-ocean ridges form along _______________________ in the crust.
 _____________________ rises through these cracks, cools, and forms new crust.
Age of the Sea Floor
 We can verify that sea floor spreading is occurring and creating new crust by testing the _____________ of rocks
on the ocean floor.
 The youngest rocks are close to spreading centers, while older rocks are found _____________________ away.
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 The oldest rocks on the sea floor are ____________________ million years old.
 ___________________________ crust can be upwards of 4 billion years old!
 Why do you think continental crust is so much older than oceanic crust?
 The ocean floor is constantly being created AND ______________________________.
Ocean Trenches
 If the sea floor is always spreading and creating new crust, why is Earth not constantly getting bigger?
 Crust is being destroyed at the same _________________ it is being created.
Causes of Plate Movement
 Remember-tectonic plates float on the _____________________________-a layer of hot, soft rock.
 ____________________________: the transfer of energy (heat) by the movement of a material.
 Convection is what happens when you boil a pot of water.
 The water at the bottom of the bottom heats up, becomes less dense and _____________________.
 At the surface, it cools, becomes more _______________________, and sinks.
 Rock in the asthenosphere acts the same way as a boiling pot of water-it moves by ________________________.
 When this rising and sinking pattern repeats, it forms a circular motion called a convection current.
 The movement of the mantle is much slower than a pot of boiling water-only a few __________________ per year!
 The movement in the asthenosphere is like heavy boxes on rollers-but moving very, very slowly.
Slab Pull and Ridge Push
 Two other possible causes of plate movement are slab pull and ridge push.
 Slab Pull: when ______________________________ pulls the edge of a cool plate into the asthenosphere.
 Ridge Push: when material from a mid-ocean ridge slides ____________________________ from the ridge.
Putting it All Together
 The theory of plate tectonics puts together scientists’ knowledge of Earth’s plates, the ocean floor, and the
asthenosphere.
 There are ____ major tectonic plates on Earth.
 One plate cannot shift without affecting the others nearby.
Review
____1. The existence of fossilized tropical plants in Antarctica indicates that millions of years ago the continent had _____.
A. a warm, rainy climate.
C. a cold, dry climate
B. been part of Africa.
D. been farther from the equator
____2. The driving forces of tectonic plates are related to convection currents in Earth’s
A. crust
C. inner core
B. mantle
D. outer core
____3. Which of these did Wegener use to support his theory of continental drift?
A. Similar rocks and similar fossils on different continents
B. Sea-floor spreading and similar rocks on different continents
C. Convection currents in the asthenosphere and sea-floor spreading
D. Fossils from ancient organisms and convection currents in the asthenosphere.
____4. Studies of the ocean floor support plate tectonics because oceanic crust
A. is younger at a ridge and older near a trench
C. is younger at a trench and older near a ridge
B. is much older than continental crust
D. is about the same age as Pangaea
_____5. Scientists think that the main driving force of plate tectonics is
A. ridge push
C. slab pull
B. convection in the lithosphere
D. convection in the asthenosphere