Geological History
What has caused the Earth’s surface to change in the last
4.6 billion years?
`
Theories and findings
Isostasy - This states that the crust floats on the mantle
since the crust is less dense and the mantle is like a flexible
plastic.
This explains why less dense continents (granite) are
higher than denser sea floor (basalt).
Continental Drift - A theory that states that all the
continents were once a single land mass which split apart.
This is Wegener’s theory about Pangaea
This explains why
1) colder climates have remnants of warmer climates.
EX. plant fossils in cold regions
2) Fossil of the same organisms found on different
continents
3) How continents seem to fit together How similar rocks
are found on different continents
Sea Floor Spreading - This states that magma pushes up in
a ridge on the ocean floor pushing the floor apart. In the
ocean trenches the crust moves down and melts. (see
drawing)
This explains the ocean floor features (ridges and
trenches). Shows how crust moves`
Paleomagnetism- The earth’s magnetic field has reversed
throughout its history. This is shown by the orientation of
magnetic rock in the crust.
Patterns of magnetism on the sea floor on both side of a
ridge support the idea of sea floor spreading