evidence for continental drift and the theory of plate ...€¦ · continental drift ! and the...
TRANSCRIPT
Evidence for Continental Drift ���
and The Theory of ���Plate Tectonics
Did you know that the coal that is mined in Pennsylvania was actually formed from tropical plant life near
the Equator? How did it travel northward to Pennsylvania? Scientists
believe that 200 million years ago, when the dinosaurs dined upon
tropical ferns and tall tropical vegetation, what is now Pennsylvania was at a different location, namely the
equatorial region. !
1. Alfred Wegener was the first scientist to suggest that the fit of the continents of South America and Africa may not be a
coincidence. He thought that the continents may have been together at some point in the past. He called this
“supercontinent” Pangaea ���(this means “all land”).
2. In 1912, he proposed the theory of continental drift, which
means that the continents have moved to their current locations.
3. Besides the “puzzle-like” fit of some of the continents, there is
substantial rock & fossil evidence to support Wegener’s theory:
a. Like animal fossils have been found oceans apart.
b. Fossils of the same green plants have been found on almost all continents, suggesting that they
all once had a similar climates.
c. Additionally, fossils of tropical plants have been found on islands in the Arctic Ocean, suggesting that area may have been much
warmer in the past.
d. Glacial deposits and weathered rock (scientists think
the is from moving ice) have been found on South America, Africa, India, and Australia. This could mean that these lands were once cold enough for glaciers to form and eventually move around on
the land.
e. Similar rock structures are found on different continents. For example, mountains in the United States are similar to ones found on Greenland and in Europe. Also,
rocks in South America and Africa are very similar.
4. The discovery of sea-floor spreading on the ocean’s floors has given Wegener’s theory of continental drift more support.
a. In the 1950’s, it was found that the ocean floors have
mountains, valleys, and ridges, just like the land on earth.
b. It was suggested (and later agreed upon) that these
formations have been caused by magma from the mantle being pushed up through the crust. Then, it flows to each
side as the process repeats. ���http://www.wwnorton.com/earth/egeo/animations/ch2.htm ���
c. This idea was supported by the dating of rock found along the ocean’s ridges. The youngest rocks are found right along the ocean’s ridges. The ages of the
rocks becomes increasingly older as you move away from
the ridges.���http://www.wwnorton.com/college/geo/earth2/home.asp#animations ���
This map shows ���the ages of the rocks that make up the floor of the
Atlantic Ocean. Red represents the youngest
rocks; the deepest red marks the Mid-Oceanic
Ridge, where continental plates are pulling apart and new crust is being
formed. Older rocks are yellow, green, and blue.
5. Also supporting the idea of seafloor spreading are clues from the earth’s magnetic
poles.
a. Think of the earth having a giant magnet in its core.
b. This creates a north and a south poles on earth. We evidence of
these poles when we use a compass.
c. Anyhow, scientists theorize that these poles have reversed several
times over the lifespan of the earth. This is supported by the discovery
of patterns in iron containing minerals and rocks (remember, iron is magnetic). Magnetic rocks are “attracted” to the north pole, so
they are pulled towards it, and away from the south pole.
Interesting…Our planet's magnetic field reverses about once every
200,000 years on average. However, the time between
reversals is highly variable. The last time Earth's magnetic field flipped was 780,000 years ago,
according to the geologic record of Earth's polarity.���
d. When the iron-containing material on earth is studied, it
shows that this pattern has changed over time. This is especially apparent on the
oceans’ floor.
e. Did you know that the magnetic north on earth is still
wandering? The magnetic pole is currently 966 km (600 miles)
from the geographic one.
6. All of this scientific work has led scientists to the theory of plate tectonics, which states that the
earth’s crust is broken in to sections which move around (or float) on the mantle below. It is this theory that helps to explain
how the earth’s surface has changed and will continue to
change over time.
So what will the earth look like in the future? We can only guess…
So what will the earth look like in the future? We can only guess…