How old is the Earth?  Why should we care?

Marli Bryant Miller
Text originally appeared as the Op-ed piece: Creationists Ignore Geologic Evidence
Eugene Register-Guard, Monday, November 8, 1999

The earth is old.   It is much older than the "Creation Scientists" would have us believe.  And it doesn't take an advanced degree to see that it's old.  All it takes is an open mind, a few observations, and some common sense.

Think of the Grand Canyon.  Millions of people visit the Grand Canyon every year and gaze a mile into the earth.  They look past more than three thousand feet of colorful, horizontally layered rock, and into the dark, steep Inner Gorge where the Colorado River flows.  The layered rock is called "sedimentary" rock.  It consists of sediment: particles of pre-existing rock such as sand or silt, or mineral precipitates from marine organisms, that, through time, become cemented into rock.  Sandstone, shale, and limestone are sedimentary rocks found in the Grand Canyon.  Because sedimentary rock accumulates in layers, the oldest rock lies on the bottom and the youngest lies on top.

By looking at places today where these same rock types form, we can estimate how long it takes for them to accumulate.  Using the fastest reasonable rates, the 3500 feet of layered rock in the Grand Canyon would take millions of years to form.

But that's not all.  Go in any direction and you will see more.  Travelling westward, the same rock units of the Grand Canyon become thicker, reaching about 30,000 feet.  We can measure that thickness because those rocks are tilted.  By walking along the ground, we can walk across and measure the layers.  If you travel northwards to Zion National Park, you will see layers of rock younger than in the Grand Canyon.  In Zion, there are 4000 feet of these younger rocks.  Beyond Zion, at Bryce Canyon, you encounter still younger rock.

Creation Scientists like to say all this material was deposited by Noah's flood, rapidly.  But what types of material would you expect to see left by such a flood?  Boulders and gravel -- not the fine-grained sand, shale, or limestone in the Grand Canyon, Zion, and Bryce.

Instead of travelling north or west, try hiking down to the bottom of the Grand Canyon.  At the top of the Inner Gorge, the horizontal layers of sedimentary rock rest on top of tilted and faulted layers of other sedimentary rock.  These sediments were deposited, cemented into rock, faulted, tilted, and then eroded flat before the horizontal layers above could accumulate.

And below the tilted and faulted layers?  An entirely different type of rock: metamorphic rock.   Look at a metamorphic rock and you'll see that it consists of small crystals which have grown together to make a crude, irregular banding.  These types of rocks can only form under conditions of high temperatures and pressures.  These rocks formed perhaps 10 miles beneath the earth's surface.

Somehow, that metamorphic rock moved from great depths below the surface up to the earth's surface where we see it today.  And because sedimentary rock was deposited on top of it, it must have come up before the sedimentary rock formed.  How long did that take?  Our fastest long-term uplift rates are on the order of 2 miles per million years.  So at minimum, uplift of the metamorphic rock took 5 million years.

This description is, of course, a simplification.  Every added detail adds more time.  What about the multiple periods of erosion through earth history that removed, rather than deposited material?  What about the several periods of mountain building that are recorded by buried fault zones and coarse-grained erosional debris?  The whole picture, which does get very complicated, is one of an earth whose surface changes over an immense amount of time.  To deny that is to miss out on much of the beauty and mystery of our planet.

Why is the age of the earth important?  From a practical standpoint, an appreciation of the earth's age is the first step in understanding nonrenewable resources and environmental degradation.  Resources form on a geologic time scale while we consume them on a human time scale.  Similarly, the earth can heal its scars, but at a rate far slower than we create them.

Symbolically, the great age of the earth drives home humanity's relative youthfulness.  For most scientists, many of whom are practicing Christians, this idea adds to the mystery and wonder of our existence.  It enhances, rather than conflicts, with their spirituality.  In fact, up until the 1960s, nearly all Christians accepted an ancient age for the earth and integrated it with their world view.  Even today, mainstream Catholics and Protestants accept an ancient age for the earth.

Today, the age of the earth is under attack by the Creation "Scientists", the same people who helped remove evolution and cosmology from the required science curriculum in Kansas.  They argued that we can't "see" evolution or cosmology.  Similarly, we can't "see" geologic time.  However, we can see the evidence for geologic time--just as with evolution and cosmology.  And to appreciate its meaning?  All it takes is an open mind and some common sense.

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