Two Reliable Tools Provide Evidence for an Old Earth
Radiometric Dating History
People who studied creation in the nineteenth century were known as “natural philosophers.” Many were Christians who contributed to the development of the science of geology by examining rocks and fossils. They observed that the great diversity of fossils was not random, but highly organized in the sedimentary layers. Wherever they looked, specific groups of fossils that were deposited more recently were always found above others. These natural philosophers developed the principle of superposition: older rocks are below and younger rocks above (hence relative age). They then named the major divisions “eras”: Paleozoic for old animal life, Mesozoic for middle animal life, and Cenozoic for recent animal life. This classification became the geologic time scale (see figure 1), and between 1820 and 1880, scientists named eleven periods after locations in Europe where the fossil groups were found. The relative age of sedimentary rocks was found to be the same in the USA and, ultimately, around the world.
Up to that time, geologists had no method of finding an absolute age (number of years old) for each of the eleven fossil systems. Then radioactivity was discovered in 1896, and when scientists understood the physics of radioactive decay, geologists realized they could determine when an igneous rock had formed in the past (as liquid lava that cooled and formed solid minerals).
The rate of radioactive decay follows the “half” rule. In each interval of time, called a half-life, half of the remaining “parent” atoms, on average, decay to become “daughter” atoms that are stable. One significant “parent-daughter” pair for radiometric dating is uranium-238 that becomes lead-206 after a long decay chain. By the end of the 1930s, geologists had developed these techniques to determine how long ago igneous rocks had formed.
Figure 1: Geologic Time Scale developed in the nineteenth century by natural philosophers. Image credit: Ken Wolgemuth
Dating Volcanic Rocks in Hawaii
The Hawaiian Islands, made of igneous rock, provide a powerful example for demonstrating that radiometric dating works. During the spring of 2018, continuous eruptions of the Kilauea volcano created rivers of lava that flowed to the coast and into the ocean—destroying forests and buildings along the way. Kilauea is one of the most active volcanoes in the world, having added 570 acres to the Big Island since 1983.
That lava comes from what geologists call a “hot spot” in the mantle (see figure 2), where lava oozes up through a plume in the oceanic crust and builds the islands. The Pacific Plate has been moving to the northwest for over 80 million years, forming submarine mountains and the Hawaiian Island chain over the last 5 million years. Kauai to the northwest is the oldest, and the Big Island with Kilauea and its current eruptions is the youngest. The Pacific Plate moves across that mantle plume at the blistering pace (geologically speaking) of a few inches per year. This process is much like moving a sheet of paper over a stationary lit candle: the movement of the paper is recorded as a trail of burn marks from the heat of the candle beneath. The Big Island presently lies over the candle, which allows for radiometric dating of the rocks.
Figure 2: The Pacific Plate moves to the northwest over the “hot spot” in the mantle, forming successive islands over geological time scales. Image credit: Gregg Davidson and Ken Wolgemuth
Hawaii’s igneous rocks all contain potassium atoms that are radioactive—potassium-40 (parent) decaying to argon-40 (daughter). Scientists have thus determined radiometric ages for many of the islands and the submarine mountains northwest of Hawaii from rocks collected by research ships. As shown in figure 3, the ages determined by radiometric dating range from 2 million years at Hawaii to 80 million years at the north end, close to the Aleutian Islands.
The total distance of these formations is 3,700 miles, which divided by 80 million years works out to an average movement of 2.9 inches per year. In addition, geologists have measured the movement between the many islands and seamounts, and it ranges from 2.6 to 3.6 inches per year (based on potassium-argon dating). The fact that we find a very regular increase in radiometric ages from the present eruptions on Hawaii’s Big Island northwest toward the Aleutian Islands (spanning 3,700 miles) demonstrates the reliability and internal consistency of the method. But this “game of inches” gets even better with additional evidence.
Figure 3: Pacific Ocean basin showing Hawaiian Islands and Emperor Seamounts with radiometric dating ages. Image credit: Gregg Davidson and Ken Wolgemuth
Measuring Plate Movcment via Satellite
Satellites allow scientists to measure the movement of the Big Island to see if the current speed of the Pacific Plate is within the range of 2.6 to 3.6 inches per year. If the radiometric dating is incorrect, then the measured speed should be nowhere close to that range. Results show the speed of the island of Hawaii today over the “hot spot” averages 3.1 inches per year!1
What this means is that we now have two independent and mutually confirming lines of evidence: (1) radiometric dating, and (2) satellite measurements of tectonic plate movement.
Some young-earth advocates suggest that radioactive decay and/or tectonic plate movement was much faster in the past. But squeezing 4.6 billion years of radioactive decay (releasing heat) into 10,000 years or less would melt the earth’s crust and boil off our oceans! And speeding up tectonic plates would also create too much heat (friction).
Radiometric dating, which continues to be refined, is a valid and powerful tool for dating rock sequences and, along with confirming satellite measurements, for establishing the age of the earth itself. God has given us amazing tools to test and verify our understanding of the earth’s history!
*I want to thank Mark McEwan and Arnold Sikkema for assistance in clarifying the text. Thanks also to the Canadian Scientific & Christian Affiliation, which first published this article as a pamphlet at https://www.csca.ca/pamphlets.
- Carol Hill, Gregg Davidson, Tim Helble, and Wayne Ranney, eds., The Grand Canyon, Monument to an Ancient Earth: Can Noah’s Flood Explain the Grand Canyon? (Kregel Publications, 2016).
- Cherry Lewis, The Dating Game: One Man’s Search for the Age of the Earth (Cambridge University Press, 2000).
- Roger C. Wiens, “Radiometric Dating: A Christian Perspective,” American Scientific Affiliation (2002), asa3.org/ASA/resources/Wiens.html.
- Gregg Davidson and Ken Wolgemuth, “How Old Are the Hawaiian Islands?” YouTube, October 4, 2018: https://www.youtube.com/watch?v=oRKEvB00cYI&feature=youtu.be.