Geography Reference
In-Depth Information
earth age of seventy-five thousand years. Don't laugh. The Comte de Buffon was no buffoon. If wide of
the mark in his calculations, he was at least making an attempt to bring scientific methods to the question.
He was simply short on good information. Long after de Buffon, other scientists tried similar experiments
with different materials.
But with the discovery of radiation early in this century, science got one of its periodic major shake-ups.
The previously unknown high heat produced by radioactivity made attempts at measuring cooling metals
by simple thermometer readings obsolete. Radioactivity produces temperatures that are off the charts. In
time, radioactive dating was discovered, giving science a much clearer notion of the earth's age.
The oldest rocks dated by science so far are about 4 billion years old. Well, that's actually 3.96 billion,
if you want to be picky about it.
Found among younger rocks in Canada, these ancient stones—which appear to have gathered no
moss—are actually grains of zircon. A brown to colorless mineral, zircon can be heated, cut, and polished
to form a brilliant blue-white gem. In Greenland, rock formations have been dated at 3.8 billion years.
*
Obviously, the earth has to be older than that, and the best estimate is 4.6 billion years old. That number,
by the way, looks like this:
4,600,000,000.
(This is the American usage of billion, meaning a thousand mil-
lion; in British usage, billion means the much larger number of one million million, or 1,000,000,000,000.)
Billion, trillion, zillion—it all seems pretty much the same. In these days of trillion-dollar budgets
being casually discussed in Washington, DC, people often forget how enormous these numbers actually
are. When you see the words
million
or
ten million
or
ten billion
, they blur into a simplistic mind picture
called Big Number. We have difficulty comprehending the difference between such mind-boggling num-
bers.
Given that 4.6-billion-year date, modern science assumes the earth was formed at about the same time
as the sun. The best guess, theoretically speaking, is that when the sun condensed out of a cloud of inter-
stellar gas, a small amount of material was left spinning outside its main body, like clothes in a washing
machine. The pull of gravity brought together materials in what are called
planetesimals
—chunks of rock
and frozen liquids ranging in size from a few feet to a few miles across. As these whirling bodies collided,
some of them merged in a process called
accretion.
Like the specks of dust that collect into dust balls under
your bed, these planetesimals began to come together to form the earth and other planets. As they gradu-
ally grew larger through accretion, these emerging planets exerted a stronger gravitational pull, gathering
in other smaller planetesimals. But some planetesimals went spinning off on their own, colliding with each
other and creating a galactic mess of cookie crumbs that are now called meteorites.
Rocks brought back from the moon by the Apollo astronauts in 1970 proved to be three to four billion
years old, younger than the earth and consequently crimping the notion that the earth and the moon were
formed at the same time. A new theory of the moon's birth that has caught on among the science guys was
originated by William Hartmann and Donald R. Davis and explained by Hartmann in his topic
The History
of the Earth.
Nicknamed the “Big Splash,” Hartmann's idea holds that the moon formed out of a collision
between the twenty-million-year-old earth and another large planetesimal that struck the earth a glancing
blow. The debris from this cosmic fender-bender was ejected into an orbit around the earth and came to-
gether to form the moon, which is made of materials similar to those of the earth's.
Were the Continents Actually Attached at One Time?
What
was
that? Did you hear a bump in the night? Perhaps it was California rubbing shoulders with the
Pacific Ocean.
