Draining the oceans reveals that
the Earth's solid surface -- its crust -- is divided into highlands and lowlands. The
highlands are the landmasses that form the continents and the lowlands form the ocean
basins.
Things to notice:
The ocean floor has mountain chains, isolated peaks, and deep valleys.
The pronounced ridge in the middle of the Atlantic ocean marks the location
of the Mid-Atlantic Ridge where new seafloor is being created by
magma rising from the mantle. Thus, the Atlantic is getting bigger
with time. The Mid-Atlantic Ridge, is also visible in the Tectonic
Plates dataset.
The Earth's crust is not a fixed, continuous shell. It is
broken into a mosaic of moving plates. As these plates move and
shift against one another they release enormous amounts of energy in the form of
earthquakes.
Things to notice:
The boundary between the Pacific plate and the North American plate is located along the
coast of California.
The movement or slip of the two plates past one another has created the San Andreas
fault, the source of many earthquakes.
This sequence shows the locations of strong earthquakes worldwide.
Things to notice:
Earthquakes tend to be concentrated at the boundaries of Earth's plates.
Volcanoes are also more frequent along the plate boundaries.
As oceanic plates are driven under continental plates,
forcing them into the mantle, they begin to melt. This produces molten rock, which rises
to the surface forming volcanoes. The locations of volcanoes
which erupted between 1960 and 1995 are shown.
Things to notice:
Like earthquakes, volcanoes are concentrated along boundaries between
Earth's plates.
