Download Evidence for Continental Drift

Evidence for Continental Drift
Science 10
• Alfred Wegener proposed the Theory of
Continental Drift in the early 20th century.
• His theory is based on several observations
Jigsaw Puzzle fit of the Continents
• Wegener proposed that millions of years ago,
all the continents were joined together as a
supercontinent he called Pangea.
Matching Geological Structures and
Rocks
• Mountain ranges that begin on one continent,
end at the coast line and then appear to
continue on a continent across an ocean.
• are also similarities between rock structures
and ages of rocks on continents that are
separated by thousands of kilometers of
ocean.
Matching fossils
• Similar fossils occur in various locations.
• The fossil of a freshwater reptile called Mesosaurus have only
been found in two places; South America and Southwestern
Africa.
• Two other land dwelling fossils, Cynognathus and Lystrosaurus
have been found throughout the continents in the southern
hemispheres, separated by vast oceans.
Paleoglaciation
• Glaciers are masses of ice
• When glaciers retreat they leave evidence of their
existence (U-shaped valleys, erratic and deeply
scratched rocks)
• Scientists have found evidence of glaciers in now
tropical areas
How do the Continents Move?
• Earth is broken into large, movable slabs of
rock called tectonic plates.
• The tectonic plates are outlined by the pattern
of volcanoes and earthquakes around the
planet.
• Volcanoes are openings in Earth’s surface that
when active spew out gases, chunks of rocks,
and molten rock.
• Earthquakes are sudden, ground-shaking
release of built-up energy at or under the
Earth’s surface.
Evidence for Continents moving
• The Mid-Atlantic Ridge is a long mountain
range running north to south down the length
of the Atlantic ocean.
• The youngest part of the Atlantic ocean floor
is closest to the Mid-Atlantic Ridge.
• The layer of ocean sediment becomes thicker
the farther is away from the Mid-Atlantic
Ridge.
• Earth’s magnetic field changes in strength
from time to time and over thousands of years
it can completely reverse in a process known
as magnetic reversal.
• In the past 10 million years, Earth’s magnetic
poles have reversed an average of four times
per million years.
• Paleomagnetism is the study of magnetic
properties of ancient rocks.
• There is a pattern of stripes in the direction
that iron containing minerals pointed on the
sea floor
• The pattern is called magnetic striping. The
pattern was repeated on both sides of the
Mid-Atlantic Ridge.
Sea floor spreading
• Magma (molten rock) from beneath the
Earth’s surface rises because it is less dense
than the material that surrounds it.
• The magma cools and hardens when it breaks
through Earth’s surface at a spreading ridge
forming new sea floor.
• As convection currents cause more magma to
rise, the new magma forces apart the
hardened material and like a conveyer belt
continuously pushes older rock aside.
• A geologic hot spot is an area where molten
rock rises to Earth’s surface in the middle of a
tectonic plate.
• Hot spots show that tectonic plates move.
• A Canadian named J. Tuzo Wilson proposed
that the continental plates must break up at
certain areas, move across Earth’s surface,
then rejoin. His theory was later named the
Plate Tectonic Theory.