Birth - The Story of Earth - page 15

tonic plates that have shifted continents and opened oceans operate in cycles of hundreds
of millions of years as well.
Physics and astronomy provide evidence for deep time that is no less persuasive. The
predictable decay rates of radioactive isotopes of carbon, uranium, potassium, rubidium,
and other elements are exceptionally accurate clocks for dating rock-forming events that
extend back billions of years to the formation of the Solar System. If you have a collection
of one million atoms of a radioactive isotope, half of them will decay over a span of time
called the half-life. Leave behind a million atoms of uranium-238, for example, and come
back when its half-life of 4.468 billion years has passed, and you'll find only about a half-
million atoms of uranium-238 remaining. The rest of the uranium will have decayed to a
half-million atoms of other elements, ultimately to stable atoms of lead-206. Wait another
4.468billionyearsandonlyaboutaquarter-millionatomsofuraniumwillremain.Theage
determinations of the oldest primitive chondrites—4.566 billion years old—are obtained
by this radiometric dating method.
But what of the many billions of years before the Solar System? Astrophysicists' meas-
urements of distant galaxies in motion point to a universe that is much older than 4.5 bil-
lion years. All galaxies are speeding away from us. Doppler shift data—the so-called red-
shift—reveal that the more distant galaxies are retreating even faster. Play that cosmic tape
backward, and everything converges down to a point about 13.7 billion years ago. That's
theBigBang.Thelightfromsomeofthesemostdistant objects hasbeentraveling through
space for more than 13 billion years.
The data on this point are unassailable. Any claim that Earth's age is ten thousand
yearsorlessdefiestheoverwhelmingandunambiguousobservationalevidencefromevery
branch of science. The only alternative is that the cosmos was created ten thousand years
agotolookvastlyolder—aconclusionfirstexpoundedbyAmericannaturalistPhilipGosse
in 1857, in his convoluted treatise Omphalos (named after the Greek word for “navel,”
because motherless Adam was created with a navel, so as to look as if he were born by
woman). Gosse cataloged hundreds of pages of evidence for an extremely ancient Earth
and then proceeded to describe how God created everything ten thousand years ago to look
much older .
Some may find comfort in this Creationist loophole of created antiquity, known as pre-
chronism. To astrophysicists' observations of stars and galaxies that are billions of light-
yearsaway,prechronistsretortthattheuniversewascreatedwithlightfromthosestarsand
galaxies that was already on its way to Earth. Rocks with ancient ratios of radioactive and
daughter isotopes, they argue, were created with just the right mixtures of uranium, lead,
potassium, and argon to make them appear much older than they really are. If you are of
this prechronist persuasion, I suggest you skip ahead to chapter 11 , “The Future.” Other-