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Bellwork 1/29
The earliest land plants did not have flowers. However, around
70 million years ago, flowering plants became the dominant
plant type in many habitats.
Which type of organism would benefit directly from the increase
in flowering plants?
A. Aquatic mammals, which are able to use the plants for shelter
B. Anaerobic bacteria, which can thrive in low oxygen environments
C. Pollinating insects, which consume nectar and pollen as food
sources
D. Carnivorous reptiles, which are able to hunt for food among the
plants
PLATE TECTONICS
The movement of Earth
Continental Drift
A.
The continental drift hypothesis – continents have
moved slowly to their current locations
All continents were once connected as one large landmass
now called Pangaea
The land mass broke apart, and the continents drifted to
their present positions
Evidence for continental drift
1.
2.
3.
a)
b)
c)
d)
Puzzle-like fit of the continents
Similar fossils have been found on different continents
Remains of warm weather plants in Arctic areas and glacial
deposits in tropical areas suggest that continents have been
moved
Similar rock structures are found on different continents
Continental Drift
B.
At first, continental drift was not accepted because
no one could explain how or why continents had
moved.
Discussion Question

Why is the fact that similar fossils have been found
on different continents considered evidence for
continental drift?
 If
fossils of similar plants and animals are found on
widely separated continents, it is more likely that the
continents had once been joined than that the plants
and animals migrated.
Seafloor Spreading
A.
B.
Using sound waves, scientists discovered a system
of underwater mountain ranges called the midocean ridges in many oceans.
In the 1960s, Harry Hess suggested the theory of
seafloor spreading to explain the ridges
1.
2.
3.
Hot, less dense material below Earth’s crust rises upward
to the surface at the mid-ocean ridges.
Then, it flows sideways, carrying the seafloor away from
the ridge
As the seafloor spreads apart, magma moves up and
flows from the cracks, cools, and forms new seafloor
Seafloor Spreading
C.
Evidence for seafloor spreading
1.
2.
Youngest rocks are located at the mid-ocean ridges
Reversals of Earth’s magnetic field are recorded by rocks
in strops parallel to ridges
Discussion Question

How could seafloor spreading be related to
continental drift?
 If
the seafloor is constantly spreading apart and
moving, it will affect and move the continents as well.
Theory of Plate Tectonics
A.
Plate movements
1.
2.
3.
4.
Earth’s crust and upper mantle are broken into sections
The sections, called plates, move on a plastic-like layer of
the mantle
The plates and upper mantle form the lithosphere
The plastic-like layer below the lithosphere is called the
asthenosphere
Theory of Plate Tectonics
B.
Plate boundaries
1.
2.
Plates moving apart – divergent boundaries
Plates moving together – convergent boundaries
a.
b.
Denser plates sink under less dense plates
Newly formed hot magma forced upward forms volcanic
mountains
Theory of Plate Tectonics
3.
Plates collide
a.
b.
Plates crumple up to form mountain ranges
Earthquakes are common
Theory of Plate Tectonics
4.
Plates slide past – called transform boundaries; sudden
movement can cause earthquakes
Theory of Plate Tectonics
C.
D.
Convection inside Earth – the cycle of heating,
rising, cooling, and sinking of material inside Earth
is thought to be the force behind plate tectonics
Features caused by plate tectonics
1.
2.
3.
E.
Faults and rift valleys
Mountains and volcanoes
Strike-slip faults – cause of earthquakes
Testing for plate tectonics – scientists can measure
movements as little as I cm per year
Theory of Plate Tectonics
Theory of Plate Tectonics
Discussion Question
What will happen if a continental plate collides with
an oceanic plate?
A continental plate with a continental plate?
Why?




The denser plate will always subduct, or bend under, the
less dense plate. Oceanic plates are denser than
continental plates, so the oceanic plate will sink under it.
When two continental plates collide, neither will subduct
because they are both less dense than the asthenosphere
beneath them. Instead, they will crumple up and form
mountain ranges
Bellwork 2/3
The following chemical equation shows the incomplete
formula for burning methanol. The question mark
represents the unknown number of oxygen (O2)
molecules.
2CH3OH + ?O2  2CO2 + 4H2O
How many molecules of O2 are needed to balance this
chemical equation?
F. 1
G. 3
H. 5
J. 6