Download File - Science 10 Enriched

Science 10 E 12.1 EVIDENCE FOR CONTINENTAL DRIFT
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Date:
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(Reference: pp. 506 - 517 of BC Science 10)
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Early maps of the world caused Wegener, in the early 20th century, to propose
the continental drift theory.
 the theory that ____________________________________________
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THE MAIN EVIDENCE SUPPORTING THE CONTINENTAL DRIFT
THEORY
Wegener based his conclusions on three main pieces of evidence:
1. THE JIGSAW PUZZLE FIT
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https://www.youtube.com/watch?v=uGcDed4xVD4
The original supercontinent was named _______ by Wegener.
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pan means all and gaea means Earth
2. MATCHING GEOLOGICAL STRUCTURES AND ROCKS
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3. FOSSIL EVIDENCE
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Examples:
 ________________fossils, a small fresh water
reptile, are found only in southeastern South
America and southwestern Africa.
 Land dwelling ________________ and
_______________fossils have been found on the
different continents in the southern hemisphere.
 _______________ fossils, a fern, are found from
South America and Africa to Australia, India and
Antarctica.
CLIMATE EVIDENCE FOR CONTINENTAL DRIFT

Work by many scientists added support to the evidence for continental drift
that Wegener had collected.

Evidence of ___________ in parts of the world that are now
tropical, such as parts of India and Africa.

Paleoglaciation: ____________________
_________________________________
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______ ___________, which form from the decomposition of
living things (usually tropical swamp material), in Antarctica .
HOW CAN CONTINENTS MOVE?
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Wegener’s evidence for continental drift did not explain how entire
continents could change locations.
•
In Wegener’s time, scientists did not know that the surface of Earth
is broken into large, movable slabs of rock called __________
__________.

New scientific equipment allowed scientists to measure the slow but
steady drift of Earth’s tectonic plates.
Observations related to the movement of the tectonic plates
 It was noted that earthquakes and volcanoes appear in certain
patterns along the edges of tectonic plates.
 ______________ are openings in Earth’s surface, that,
when active, spew out gases, chunks of rock, and melted
rock.
 An ________________ is a sudden, ground-shaking release
of built-up energy at or under Earth’s surface.
 Mapping of the ocean floor revealed the _____-__________
________, a long mountain range running down the middle of the
Atlantic Ocean.
Evidence from ocean rock and sediments
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The rocks closest to the Mid-Atlantic Ridge were
_______________ than other ocean rocks.

Sediments along the ridge became _____________ farther away
from the ridge.
Evidence from paleomagnetism

Like a bar magnet, Earth has north and south magnetic ______
and a ____________ ________.
 Iron and other magnetic metals in rocks also usually align
with these field lines.

Earth’s magnetic field is not unchanging, however.
 It not only changes in strength from time to time but, over
thousands of years, its direction can completely reverse, a
process known as _____________ __________________.

scientists think that Earth’s magnetic field is
produced by the motion of _______ _____ in the
planet’s interior.
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normal polarity: when Earth’s magnetic poles are
___________ to its geographic poles, as they are
now.
 A compass needle would point in the
general direction of the geographic _______
Pole.
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reverse polarity: when Earth’s magnetic poles
reverse so that they are ____________ to Earth’s
geographic poles.
 A compass needle would point in the
general direction of the geographic
________ Pole.
 Paleomagnetism: _________________________
_________________________________________
 rocks along the ridges show a pattern of stripes in
the direction that iron-based minerals are pointing
on the sea floor.

The pattern, called ___________ ___________,
occurs on both sides of the ridge and corresponds
with reversing magnetic fields
SEA FLOOR SPREADING: AN EXPLANATION
•
Hess suggested that magma rose to form new rock at certain places.
 Magma: ____________________________________
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Like other fluids, it rises and falls due to ____________
differences (convection).
 The convection currents of magma formed a ______________
___________where they broke through Earth’s crust.
 sea floor spreading: ___________________________
___________________________________________
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Like a “new crust” conveyer belt
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Magnetic striping of basalt rock shows long stripes of new
rock moving away from ocean ridges and also reveals the
direction of Earth’s magnetic field at that time.
•
Wilson combined the concepts of sea floor spreading and paleomagnetism
to explain continental drift.
 He suggested that chains of volcanic islands, such as the
______________ ____________, were formed when a tectonic
plate passed over a stationary _____ ______.
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hot spot: ______________________________
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 He thought that continents must break up at certain areas, move
across Earth’s surface, and then rejoin.
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This explained the formation of ____________ and
_______ _______ and the cause of _______________ and
___________ eruptions.
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This also gave a reason for the movement of ___________
________ and helped explain the transformation of rocks
from one type to another in the rock cycle.
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Later named the ________ _________ _________,
the unifying theory of geology.