Thursday, June 30, 2005


A Journey Through Time: Rocks of Ages

A granitic intrusion in the Vishnu Schist along Hermit Creek near the Colorado River in the Grand Canyon. The presence of rock from volcanic origins allows precise radiometric dating.

Third in a series on the age, formation and geology of the Grand Canyon.

We have dealt with the assertion by creationist John Turney in a commentary in the Cincinnati Enquirer that "evolutionists" assume that "the Grand Canyon's rock always had its current concrete-like consistency." (Scroll down to read our earlier posts.)

Today, RSR will take a look at Mr. Turney's second assertion: "[Evolutionists] were not present during the Grand Canyon's formation. Therefore they turn their assumptions into "fact." What they conveniently fail to mention is that geologically younger rocks are near the bottom of the Grand Canyon, while geologically older rocks are near the top. This is the reverse of what should be found if evolutionary theory were true."

True, no "evolutionist" or geologist was there during the Grand Canyon's formation, but, that doesn't mean we can't learn how it happened by studying the canyon as we now find it. One of the ways that geologists study the history of the earth or a geological feature such as the Grand Canyon is to observe the geological processes that are occurring today -- volcanism, deposition of sediments, erosion, plate tectonics -- to understand how geological features were created in the past.

This is something human beings do all the time. As the popular CBS television show "CSI" demonstrates -- in a somewhat over-dramatic fashion, the methods of science can be used to reconstruct events that happened in the past -- such as a murder -- that no outside observer has witnessed. That evidence is so convincing, it can be used in a court of law to convince a jury of the guilt of a murderer.

The evidence about the formation of the Grand Canyon is as convincing as any forensics testimony introduced into a court of law -- real or dramatized.

Now, let's get back to the canyon...

Below the Tonto Plateau as our group hiked down the last few miles to the Colorado River along Hermit Creek, the canyon narrowed. We were entering the inner gorge. The rock strata turned black. We were now hiking through the Vishnu Schist, an early Pre-Cambrian metamorphic rock first laid down as sediments of shale, sandstone, and limestone beginning about 2 billion years ago.

These sediments were metamorphosed by the enormous heat and pressure of volcanic action -- the result of plate tectonics.

As the sediments of the Vishnu Schist were being metamorphosed, molten magma intruded into seams in the rock forming the Zoroaster Granite. This is important to geologists, because rock from volcanic action, such as the Zoroaster Granite, can be quite accurately dated using radiometric methods.

All volcanic rocks and minerals contain minute amounts of radioactive material. These radioactive elements are unstable, over time they spontaneously decay into more stable atoms.

This decay occurs at a constant rate specific to each isotope -- isotopes are different forms of a single element that have the same number of protons but different numbers of neutrons in their nuclei. The rate of decay is usually described in terms of a half-life. Uranium 238 is an example of chain decay. It has a half life of 4.5 billion years. It decays into a stable daughter product, lead 206. Uranium 235, with a half life of 708 million years, decays into lead 207.

By looking at the ratio of parent to daughter isotope, geologist can determine the age of the rock. By looking at the ratio between both Uranium 238 and Uranium 235 and their respective daughter isotopes, geologists get a check on the date of the rock they are testing.

Geologists can also observe simple decay, an example of which is the decay of the isotope Rubidium 87 into the stable daughter atom Strontium 87, or they can use branching decay, as when the isotope Potassium 40 decays into Argon 40 and Calcium 40. In the latter case, 12 percent of the resulting daughter atoms will be Argon 40 and 88 percent will be Calcium 40.

Thus, the most accurate time piece known to humankind -- the atomic clock -- can be used to date the rock of the Grand Canyon -- and to refine and confirm the other data we've looked at over the past few days that, taken together, make an irrefutable case for the ancient age of the Grand Canyon.

Tomorrow, we'll look at human habitation of the Grand Canyon and another dating technique: Carbon 14 that allows us to date objects of biological origin.

Part 1: Journey Through Time
Part 2: Dynamic Forces
Part 4: Human Habitation of the Canyon


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