The Age of the Earth

Rounding the Four Corners – November 2010

by Larry Larason

Sir Ernest Rutherford, chemist and Nobel Prize Laureate.

One of mankind’s oldest questions is “How old is the Earth?”  In 1650 Archbishop James Ussher published a chronology of the world from creation to “modern” time.  Rather than studying nature, he attempted to date all the events in the Bible.  The Archbishop studied it all, including the long list of begats in Genesis, to come up with the birth of our world on 26 October, 4004 B.C.  In his time line the Noachian Flood occurred at 2348 B.C., and David defeated Goliath in 1063 B.C.  He also accepted all those improbable lifetimes mentioned in Genesis, such as Adam living 930 years and Methuselah for 969!   Correcting for the changes in calendars over the ages he decided that Jesus was born in 4 B.C.

I first learned about Ussher’s chronology while I was an undergraduate.  At that time I couldn’t see how someone could disregard the evidence of great antiquity displayed in the world around us.  Look at mountains, at big canyons, the thick layers of sedimentary rocks.  They could not have been created in such a short time.  Consider the evolution of all the plants and animals.  That semester I was also taking a course in creative writing, so I wrote a snotty little poem about him.

Archbishop Ussher was born on a yesterday,

Wrapped up the cosmos in brown butcher paper,

And dribbled out stars all the way up to Coventry.

Four thousand four B.C?  Indeed!

Note: About 1648, during the English Civil War, Cromwell sent some royalist prisoners to be incarcerated at Coventry.  The jailors fed the prisoners but would not speak to them.  Since then the phrase “send to Coventry” has meant to ostracize someone.  This was often used during labor disputes when strikers would ignore strike-breakers, not even acknowledging their presence.  Sorry, but I felt I had to explain why Ussher would take the cosmos to Coventry.  Actually, he was Irish, so he probably wouldn’t have gone there anyway.  Coventry was also where Lady Godiva rode naked through town to protest taxes.  [I hope the Tea Partiers don’t decide to emulate her!]

Ussher’s chronology was not the only one of its kind produced in the seventeenth century.  Each had slightly different dates.  Ussher’s was the most meticulous, and his dates were adopted to be printed in the margins of the King James translation of the Bible.  Although Ussher’s chronology is still adhered to today by “Young Earth” creationists, the Archbishop himself would probably disown it because he believed in science.  Also, he knew that the Bible was not inerrant: he found conflicting information in the Christian versions available in his time, so he used a Jewish version of the Old Testament as the most reliable.

Even while Ussher was working on his chronology, others, including Nicolas Steno in Denmark, were seeing evidence of great antiquity in the rocks and succession of fossils.  When geology began challenging the Bible-based chronologies in the eighteenth century, some clung to the older view and said the geology of the present day was the result of a catastrophe – Noah’s flood.  You find a thick layer of sandstone?  Noah’s Flood made it.  You find sea shell fossils on top of mountains?  Noah’s Flood put them there.  The flood was seen as the answer to nearly everything.

Instead, geologists formulated the doctrine of uniformity: the processes operating today are the same that shaped the landscape in the past, and, therefore, change was gradual rather than sudden and catastrophic.  But geologists had no way of dating past events.  They knew that this rock was older than that one but couldn’t say by how much.

Lord Kelvin [aka William Thompson, 1804-1907] was a distinguished scientist, whose achievements are too numerous to list here.  But in 1866 he attacked the fledgling science of geology.  He claimed that the Earth could not be more than 100 to 500 million years old, and he preferred the smaller number.  He later lowered it even more.   He based this conclusion on his work with thermodynamics.  He assumed that the planet began as a molten ball of uniform composition and had been losing heat ever since.

Kelvin’s reputation was such that anything he wrote had to be taken seriously.  Many geologists didn’t like his idea, but lacked data to refute it.  Charles Darwin also objected to Kelvin’s pronouncement, because he knew that humans had not evolved from single-celled creatures in such a short time.  Although many scientists at the time accepted Kelvin’s figures, they were soon proven wrong.  As Stephen Jay Gould pointed out, Kelvin built his estimate on too many [wrong] assumptions and too few data.*

Lord Kelvin did allow himself an “out.”  In one of his papers he asserted that his figures were correct “unless someone discovered extra sources of heat” in the Earth.  The extra source – radioactivity – was discovered in Kelvin’s lifetime, but he never revised his estimate of the age of our planet.

Radioactivity was discovered and investigated by scientists such as Antoine Becquerel, Pierre and Marie Curie, and Ernest Rutherford in the 1890s and early 20^th century.  Not only does radioactivity release heat – radium produces enough heat to melt an equal amount of ice in less than an hour– but it also provides the clock that geology needs.  Radioactive elements are unstable and decay at a fixed rate called the half-life.  This is the period of time required for half of the radioactive element to decay into another element or isotope.  By measuring the ratio of an unstable element to the amount of decay product in a given mineral [a crystal is best] you can determine when the rock formed.

Rutherford performed one of the early experiments to try to date the Earth.  As uranium decays it emits alpha particles.  These particles, two neutrons plus two protons, are the same as the nucleus of helium.  The alpha particle picks up two electrons and then is helium.  Rutherford found helium in “bubbles” in rocks containing uranium.  He figured from the ratio, given the half-life of 4.47 billion years for uranium, that the Earth was at least 500 million years old.  Some of the helium must have escaped from the bubbles, because his estimate was still off by quite a bit.

A better radiometric measure is the ratio between the uranium and other decay products, especially the end one: lead.  There are also other means of age measurement employed by geologists now, depending on the situation.

Some actions such as earthquakes, floods, volcanic eruptions, or landslides can alter a landscape quickly.  But otherwise, within a human lifetime geological change is nearly imperceptible.  Radiometric dating provides a longer view of changes in the Earth.  Careful analysis of radioactive rocks since Rutherford’s time has shown the Earth to be 4.5 billion years old.  It seems ironic that the half-life of uranium is nearly the same as the life of the Earth to date.

*The essay “False premise, good science” is included in his collection The Flamingo’s Smile [1985].

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In September I wrote about Billy the Kid.  I asked readers to tell me their opinions of the outlaw.  I received only two responses.  One agreed with my assessment; the writer said, “If I never hear about him again that would be fine with me!”  The other was a thoughtful email by someone who believes, but cannot prove, that Billy was involved in a secret organization, similar to Las Gorras Blancas, working to preserve Hispanic ownership of land after the U.S. took over New Mexico.  If that were proven, it would certainly make Billy a more interesting historical figure than does his present criminal image.