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Convection and the
mantel
Section 2
Vocabulary for week 5
Convection currents
 Continental drift
 Fossil
 Alfred Wegener
 Mesosaurus

Review

Types of heat transfer
– Radiation
– Conduction
– Convection
define all of these.
Convection

The one the most important to us is
convection.
– Convection currents: the movement of a fluid
caused by the differences in temperature that
transfers heat from one part of the fluid to
another.
 Why is this important?
– these convection currents are part of what cause the
earths magnetic field and are a part of the driving force
in plate tectonics.
Continental drift

The world hasn't always looked the same.
– Once only Europe existed
– and the world was flat
– The Americas were not connected
– Only the east cost was discover
– Then in the 1700 geologist were sure that the
contents never moved
Continental drift continued

In 1910 a young German scientist
suggested something amazing, he figured
out that the continents all fit together like
a jigsaw puzzle.
– Alfred Wegener was the first to hypothesize
that earth continents moved.
 He was also the first to suggest that all of the
continents drifted together to form Pangaea.
– Pangaea: single landmass that broke apart 200 million
years ago, and gave rise to today's continents
Evidence

Evidence from land features
– Mountains
 Wegener found that when he pieced north and
south America together that the mountain ranges
lined up.
– Coal deposits
 He also noticed that the coal deposits in Europe
matched up with the coal fields in North America
More evidence

Evidence from fossils
– He found a fossilized fern (Glossopteris) that
grew in a very specific time, on 5 different
continents Africa, South America, Australia,
India, and Antarctica. This is very strong
evidence that all of the land where the ferns
grew was at a different place than now. The
ferns need a warm moist climate to grow and
Antarctica isn't either of those.
And even more Evidence

Evidence from climate
– in South Africa there are places where
glaciers have been proven to have existed in
the past. But the climate now in South Africa
the climate is much to warm and mild.
And even more evidence than
before

The geological community believed that
mountains were formed because the earth
was cooling, and the crust acted like an
apple skin and it would wrinkle. Wegener
said that if that’s the case we should
mountains all over the place, but they are
only found at the edges of continents. He
suggested that the continents collided
causing a lifting or crunching
Rejected

Not so fast
– Even with all of his other evidence Wegener
couldn't prove HOW the continent moved he
didn’t have the technologies to prove it. So
the geological community wouldn’t accept his
theory.
Today

With today's info we know how they move
and that Wegener’s explanation and
hypotheses were correct.
Convection Currents Quiz

1. how do convection currents work?

2. refer to the drawing on the board
correctly name what it is asking for.

3. who was the first person to come up
with the idea that the continnets moved?
Convection Current Quiz cont.

4.What year did he come up with the
idea?
5. what was fossilized and how many
different continents was it found on,
 Bonus:
 6.list all of the continents the fossil was
found on.

Sea floor spreading

What is sea floor spreading?
– The process by which molten material adds
new oceanic crust to the sea floor.
– What effect does it have on us?
 It moves the plates and spreads out the
continents.
 Where does this happen?
– At the mid-oceanic ridges
 Mid-oceanic ridge: an undersea mountain chain
where new ocean floor is produced; a divergent
plate boundary
Sea floor spreading

In sea floor spreading the sea floor
spreads apart along both sides of the midoceanic ridge as new crust is added. As a
result, the ocean floor moves like
conveyor belts, carrying the continents
along with them.
– Who came up with the idea of sea floor
spreading?
 Harry Hess. In 1960
Evidence for seafloor spreading

There are three main types of evidence for
Hess theory.
– Molten material
– Magnetic stripes
– Drilling samples
Evidence from molten material

In the 1960’s scientist were able to dive to
the ocean floor in Alvin a small submarine
designed to take the enormous amount of
pressures at the bottom of the ocean.
– When they got down there they saw pillow
shaped or they look like they just got
squeezed from a tube of tooth past shaped
rock formations.
 These can only be formed when molten material
come in contact with seawater immediately after
reaching the surface.
Evidence from magnetic stripes

Magnetic stripes are when patterns in the
seafloor made when the Earth Magnetic
poles switch.
– When the poles switch the magnetic metals in
the molten material will line up to the north,
then when it switches they line up to the new
north or current south.
 This leaves a time line for two things 1st we know
how old the sea floor is at different places 2nd we
know when the last time the poles switched was
– 780,000 years ago.
Evidence from drilling.
Drilling
 A ship called the Glomar Challenger was
designed to drill into the ocean floor,
through 6 km of water. These samples
were examined by scientist and dated
every time the youngest rocks came from
the ridges and the oldest rocks were the
farthest away. Proving that seafloor
spreading was taking place.

Subduction

What is subduction?
– Subduction: is the process by which the ocean
floor sinks beneath a deep-ocean trench and
back into the mantle .
 Think of a conveyer belt, new crust is made at the
mid-oceanic crust and as it gets farther away from
the ridge it gets cooler and denser. This causes it
to sink at the trench where is goes down into the
mantle.
How it works.
What effect does this have?

When old crust is taken faster then new
crust can be made the ocean start to get
smaller and when new crust is made
faster then the old crust is taken the
ocean is getting bigger.
– Is this happening today?
 Yes the Pacific ocean is getting smaller and the
Atlantic ocean is getting bigger.
The end