Geography Reference
In-Depth Information
Puzzle solved!
Imagine a mountain range about 10,000 miles long and nobody knew it existed until the latter half of
the twentieth century. Sound bizarre? Well, it really happened, and of course, there's a catch of sorts.
The range in question is the Mid-Atlantic Ridge. As the name implies, it pretty much runs down the
middle of the Atlantic Ocean. It was virtually unknown until ocean-floor mapping (a very deep sub-
ject!) revealed its presence.
Through use of remotely controlled submersibles that carried cameras and other instruments, it was
learned that this mountain range is basically a 10,000-mile long active volcano. The Mid-Atlantic
Ridge is the product of
magma
, molten material from beneath the asthenosphere. A series of deep
cracks, or
fissures
, in the lithosphere run the full length of the Ridge. Over the years, magma has
oozed upwards through the fissures in response to tectonic force
piled up on the ocean floor
hardened to form the Mid-Atlantic Ridge
But this oozing is ongoing. Slowly, but inevitably, other magma is rising up through the fissures,
to cool and harden, and in doing so, elbowing to either side of the fissure the previously hardened
magma. The result is a
spreading sea floor
. The Atlantic Ocean is getting wider. The New World and
the Old World are moving apart.
Subsequent deep-ocean mapping revealed other spreading sea floors in other oceans. Here was the
explanation of how continents had split apart and moved! Here was the solution to the great puzzle
that had been driving people nuts for years
Getting Down to Theory: Earth Benedict?!
In a manner of speaking, Earth's lithosphere is like an eggshell — a thin, hard, brittle outer covering
that encases a big mass of goo. Due to tectonic force, that earthly eggshell has broken into many
pieces. Now, I want to be careful with this eggshell analogy. Just about everybody has dropped an egg
and dealt with the mess that resulted. That won't happen to Earth. You have no cause for a nightmare
in which your home planet becomes scrambled Earth, or Earth Benedict. Just remember that, like an
eggshell, Earth's lithosphere is a brittle veneer that bears no resemblance to what is inside, and is eas-
ily cracked.
