Transcript Wegener`s Hypothesis

Bell Questions 9/14/11
1. What do scientists believe the Earth was
formed from?
2. How old have scientists calculated the
earth to be?
3. List three things the earth and the moon
have in common.
Wegener’s Hypothesis
• Continental drift the continents once
formed a single landmass, broke up, and
drifted to their present location
• Proposed by Alfred Wegener in 1912
Wegener’s Evidence
• Fossil Evidence: fossils of the same plants and
animals could be found in areas of continents
that had once been connected.
• Evidence from Rock Formations: ages and types
of rocks on different coasts matched.
• Climatic Evidence: changes in climatic patterns.
Places that are now tropical show evidence of
glaciers.
Bell Questions 9/15/11
1. How are most mountain chains like the
Alps formed?
2. What freed life forms from the ocean?
3. What kind of rock made up the first
landmass?
Wegener’s Missing Mechanisms
• Wegener proposed that the continents
moved by plowing through the rock of the
ocean floor.
• Disproved by geologic evidence.
Mid-ocean ridge
Mid-ocean ridge - a long, undersea
mountain chain that has a steep, narrow
valley at its center.
Mid-ocean ridge
Discoveries about the
Mid-ocean ridge
1. The sediment that covers the sea floor is
thinner closer to a ridge than it is farther from
the ridge
2. The ocean floor is very young. 175 million
years old compared to rocks on land 3.8 billion
years old.
3. Rocks closer to a mid-ocean ridge are younger
than rocks farther from the ridge.
Mid-ocean ridge
Sea-Floor Spreading
• Sea-floor spreading the process by
which new oceanic lithosphere (sea floor)
forms as magma rises to Earth’s surface
Sea-Floor Spreading
As the ocean floor spreads apart, magma rises to
fill the rift and then cools to form new rock.
Sea-Floor Spreading
Sea-Floor Spreading
Paleomagnetism
• Paleomagnetism the study of the
magnetic properties in rock, specifically
the alignment of magnetic minerals as it
relates to the reversal of Earth’s magnetic
poles.
Magnetic Reversals
• Earth’s magnetic poles don’t stay in the
same place.
• Rocks with magnetic fields that point north
(normal polarity)
• Rocks with magnetic fields that point south
(reversed polarity)
Paleomagnetism
Magnetic Symmetry
The pattern of magnetic
symmetry indicates
that new rock forms at
the center of a ridge
and then moves away
from the center in
opposite directions.
Wegener Redeemed
• Sea-floor spreading was the mechanism
that verified Wegener’s hypothesis of
continental drift.