The face of the Earth is always changing and throughout
geologic history oceans have been created and destroyed.
Modern geologic evidence indicates that the ocean bottom is
moving at a rate from about one-half to six inches a year
through a process called plate tectonics.
Roughly 200 million years ago the Earth's surface was very
different from the familiar pattern of land we know today.
All of the land masses were grouped together into one vast
supercontinent called Pangaea. The rest of the globe was
covered by a single great ocean known as Panthalassa.
Pangaea broke up with part of the continent
drifting north and part south. 1) The northern part
split to form the North Atlantic Ocean 208-146
million years ago (mya). 2) The South Atlantic and
Indian oceans began to form 146-65 mya. 3) The
continents continue to drift. Today the oceans are
still changing shape; the Atlantic Ocean gets wider
by a few inches each year.
Slowly, over millions of years, the great land mass split
apart. The pieces began to move over the Earth's surface
driven by slowly churning currents in the molten rocks
beneath the Earth's hard outer layers. The gigantic plates
on the Earth's crust move like a conveyor belt. As new areas
of ocean floor form at mid-ocean ridges, old areas are
dragged down, or subducted, into the Earth's mantle, which
explains why the older rocks cannot be found.
By about 35 million years ago the pattern of land and sea
was very much like it is today. But the continents are still
moving and as the Atlantic and Indian oceans continue to get
wider by a few inches every year, the Pacific is slowly
shrinking. At the northeast corner of Africa we can see the
start of a new ocean. For the last 25 million years, the Red
Sea has been widening. If it continues at the same rate, in
200 million years it will be as wide as the Atlantic is
THE CHANGING OCEANS
Some related sites of interest
- The Pangaea theory was treated with much skepticism
when it was first raised. But since then, there has been
much evidence to support this theory.
- Tour a hydrothermal vent system as scientists might
encounter along the Juan de Fuca Ridge in the Pacific
- The most productive volcanic systems on Earth are
hidden under the ocean. The magma and lava of submarine
volcanoes create the edges of new oceanic plates.
- Volcanoes, mid-oceanic ridges, and deep-sea vents are
all associated with sea floor spreading and plate
tectonics. They are also the newest places on Earth.
Locate the Earth's "hot spots" in this activity.
If the oceans are always changing where
does the water come from to fill ocean basins?