Deep Core Dating and Circular Reasoning

Many Christians are reluctant to accept the Bible’s clear teaching of a recent creation because they believe secular dating methods prove that the earth is extremely old. The apparent agreement between seemingly independent dating methods is seen as a powerful argument for millions of years. But closer inspection reveals that these methods are not truly independent, and the agreement between them is the result of circular reasoning.

Dating Rocks and Fossils: Circular Reasoning

Because secular scientists believe Earth’s sedimentary rocks were deposited over millions of years, they assume a given rock layer represents a “snapshot” of the history of life at a certain time in the “prehistoric” past. Since they also think some organisms lived only during certain periods of Earth history, they conclude that these fossils can be used to date different rock layers. For instance, suppose one particular organism has so far been found only in rocks thought to be between 200 and 180 million years old. If such an “index fossil” is found in a different rock of unknown age, secular scientists tend to assume that particular rock to also be between 200 and 180 million years old. In other words, the fossils found in rocks are used to date other rocks.

But how does one determine an age for the initial set of rocks? One might assume those ages are obtained either directly or indirectly from radioactive dating techniques. In theory, yes, but secular scientists have been known to reject such ages if they contradict the evolutionary story the scientists think the fossils are telling—even if the dates from multiple methods agree with one another.1

So in the final analysis, the fossils (i.e., the assumed evolutionary story) are used to date the rocks, and the rocks are used to date the fossils (Figure 1). This kind of circular reasoning is also present in the dating of ice cores and seafloor sediments.

Deep Ice and Sediment Cores

To study past climates, scientists drill and extract cylindrical rods of ice, known as ice cores, from the Greenland and Antarctic ice sheets. These cores can be thousands of meters long, and secular scientists routinely assign ages of hundreds of thousands of years to the deepest ice within these cores. However, creation scientists can plausibly account for the excessive ages assigned to these cores, as past articles have demonstrated.2-4

Likewise, scientists also extract long cores from the ocean floor. These cores are composed of sediments that have settled on the ocean floor over time. Because deep-ocean sediments are so thick, secular scientists assume they were deposited over millions of years. This might seem reasonable since sediments accumulate very slowly today. But there is good reason to suspect that the bulk of these ocean sediments were deposited in the last half of and very shortly after the global Flood of Noah’s day.5 Because of their belief that “the present is the key to the past,” however, secular scientists ignore these clues and assume that seafloor sediments have always been deposited very slowly.

The Milankovitch Ice Age Hypothesis

Secular scientists use the Milankovitch (or astronomical) ice age hypothesis to assign ages to seafloor sediments. Supposedly, ice ages are triggered by decreases in the amount of summer sunlight falling on the high northern latitudes. These decreases in sunlight are thought to be caused by slow, gradual changes in the tilt of Earth’s axis and the shape of its orbit around the sun (see the inset in Figure 2). They think this reduction in sunlight causes the high-latitude ice sheets to increase in size, resulting in an ice age. Later, when the high-latitude summer sunlight increases, the ice sheets supposedly retreat, resulting in a warmer “interglacial” period. Because secular scientists believe the solar system is billions of years old, they feel free to extrapolate these motions back millions of years into the supposed past. They then run the numbers and calculate the approximate times the ice ages supposedly occurred.

Chemical Clues in the Sediments

Many of these researchers believe chemical clues within both the seafloor sediments and ice cores tell a story of past climate change. In particular, they make measurements of a heavy variety, or isotope, of the oxygen atom, as well as measurements of a lighter oxygen isotope. They then calculate a quantity called the oxygen isotope ratio, denoted by the symbol δ18O. This quantity has been tied to presumed past climate values. If one plots these values on a graph, many “wiggles” are apparent at different depths within a sediment core (Figure 3). Within the seafloor sediments, very high δ18O values are thought to indicate the times at which Earth had the greatest amount of ice. Sediments containing these values are thus thought to have been deposited at times of maximum ice coverage. Likewise, sediments containing very low δ18O values are thought to have been deposited when Earth’s global ice cover was at a minimum.

Secular scientists use the Milankovitch hypothesis to calculate the times of past ice ages. They then either assign these calculated ages directly to a sediment core or indirectly by matching chemical wiggles in one sediment core with those in another core (Figure 3). Similar wiggles in one core are often assumed to indicate the same age as those within another core, even if the cores are located thousands of miles apart.

Example: New Zealand Sediment Core MD97-2120

This process of tying wiggles in one core to those in other cores can be demonstrated by considering a 36-meter-long core designated as MD97-2120 that was retrieved off the eastern coast of New Zealand.6 This core’s location is indicated by the A in Figure 2. The core was divided into four sections, and a summary of the methods used to date the sections is posted online.7 Below is a description of the way scientists dated these four core sections.8

Dating of the Top Two Core Sections

Secular scientists used the carbon-14, or radiocarbon, dating method to assign ages to the first section of the New Zealand core since the method is thought to be capable of dating carbon-containing specimens believed to be tens of thousands of years old. However, most people don’t realize these radiocarbon ages must first be calibrated. Even secular scientists often do not trust a raw radiocarbon age to give the true calendar age of a specimen. In this case, the scientists used a “marine calibration data set” to convert these radiocarbon ages into calendar ages. But this calibration data set was tied to tree rings, corals dated by another radioisotope dating method, and banding patterns called varves found within marine sediments.9 Moreover, this process involved many additional assumptions.

Likewise, radiocarbon dating was used to obtain ages for the second section of the core. But the radiocarbon calibration used for the first core section did not go beyond 24,000 years. Since secular scientists believe this part of the core is older than 24,000 years, they needed some other way to calibrate these radiocarbon dates. So they used another method.10 But this calibration was obtained from chemical wiggles in a sediment core near Iceland (point B in Figure 2). And those chemical wiggles were in turn tied to chemical wiggles within the GISP2 ice core of central Greenland (point C).

Dating of the Third Section

To obtain dates for the third section, researchers tuned chemical wiggles in the New Zealand core to wiggles in a sediment core extracted off the coast of Portugal (point D).11 But preliminary ages for the top of this Portuguese core came from another nearby sediment core, and more refined ages came from Greenland’s GRIP ice core, located near the GISP2 core (point C). But the ages for the deepest part of the GRIP ice core were tied to an ice core age model that assumed millions of years and that had been tweaked to agree with Milankovitch expectations (point E).

Likewise, the Milankovitch hypothesis was used to obtain the ages for the bottom section of this Portuguese core.

Dating of the Fourth Section

In order to date the fourth core section, chemical wiggles within the New Zealand core thought to indicate past sea-surface temperatures were tuned to chemical wiggles in the Vostok ice core from Antarctica (point G).12 But the ages for the Vostok chemical wiggles came from an age scale constructed from two deep sediment cores off the coast of western South America (point F). And that age scale in turn was tied to the Milankovitch hypothesis (E) and layer counts within the upper section of the GISP2 ice core (C).

Clever Reasoning...or Self-Deception?

So, the general agreement between the ages assigned to different ice and sediment cores is not really surprising since the dating methods are linked to one another. Even so, the different methods still sometimes conflict.13

If the Milankovitch hypothesis were actually true, then one might argue that there is nothing wrong with tying chemical wiggles from one core to another. But there are good reasons to doubt this hypothesis. It is not apparent that subtle decreases in sunlight are sufficient in and of themselves to cause ice ages, and secular scientists do not have a clear explanation of how these subtle changes could be amplified to produce significant climate change. Furthermore, the hypothesis suffers from multiple other problems. And if the Milankovitch hypothesis isn’t true, then “wiggle matching” is really just a giant exercise in circular reasoning.

Wiggle matching is also problematic because seafloor sediment chemical wiggles are often obtained from the shells of free-floating organisms called planktonic foraminifera (forams). When these creatures die, their shells become part of the sediments accumulating on the ocean floor. The oxygen isotope values from these shells depend upon both the temperature and chemistry of the surrounding water at the time the shell was formed. Of course, there is no way to know these quantities, and secular scientists must make assumptions about the past in order to fill in the details. Likewise, ocean temperatures can vary dramatically due to differences in depth—remember, these particular forams float freely in the oceans—and local temperature changes may be totally unrelated to changes in worldwide climate. Therefore, it is very risky to tie chemical wiggles from one core to another core thousands of miles away, especially if the wiggles were obtained from the shells of planktonic forams.

Therefore, no Bible-believing Christian should be intimidated by the long ages assigned to the deep seafloor sediment and ice cores or by the apparent agreement between those assigned ages. Secular scientists simply assume evolution and an old earth and use those assumptions to ensure results that agree with their worldview. Despite constant claims to the contrary, deep core dating does not disprove the Bible’s history of a recent creation.


  1. Lubenow, M. L. 1995. The pigs took it all. Creation. 17 (3): 36-38.
  2. Hebert, J. 2014. Ice Cores, Seafloor Sediments, and the Age of the Earth, Part 1. Acts & Facts. 43 (6): 12-14.
  3. Hebert, J. 2014. Ice Cores, Seafloor Sediments, and the Age of the Earth, Part 2. Acts & Facts. 43 (7): 12-14.
  4. Hebert, J. 2015. Thick Ice Sheets: How Old Are They Really? Acts & Facts 44 (6): 15.
  5. Hebert, J. and T. Clarey. 2015. Ice Cores, Seafloor Sediments, and the Age of the Earth, Part 3. Acts & Facts. 44 (1): 10-13.
  6. Pahnke, K. et al. 2003. 340,000-Year Centennial-Scale Marine Record of Southern Hemisphere Climatic Oscillation. Science. 301 (5635): 948-952.
  7. Pahnke, K. et al. 2003. 340 Kyr SW Pacific δ18O Data and Mg/Ca-based SST Reconstruction, IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series 2003-057. NOAA/NGDC Paleoclimatology Program. Posted on, accessed December 15, 2015.
  8. Space does not permit me to cite every reference since this is a very convoluted process. However, I have tried to list the most important reference papers, and, for the interested reader, more documentation is provided in my technical article. See Hebert, J. 2015. The Dating “Pedigree” of Seafloor Sediment Core MD97-2120: A Case Study. Creation Research Society Quarterly. 51 (3): 152-164.
  9. Stuiver, M. et al. 1998. INTCAL98 Radiocarbon Age Calibration, 24,000-0 cal BP. Radiocarbon. 40 (3): 1041-1083.
  10. Voelker, A. H. L. et al. 2000. Radiocarbon levels in the Iceland Sea from 25-53 kyr and their link to the Earth’s magnetic field intensity. Radiocarbon. 42 (3): 437-452.
  11. Shackleton, N. J., M. A. Hall, and E. Vincent. 2000. Phase relationships between millennial-scale events 64,000–24,000 years ago. Paleoceanography. 15 (6): 565-569.
  12. Shackleton, N. 2000. The 100,000-Year Ice-Age Cycle Identified and Found to Lag Temperature, Carbon Dioxide, and Orbital Eccentricity. Science. 289 (5486): 1897-1902.
  13. Hebert, J. 2014. Circular Reasoning in the Dating of Deep Seafloor Sediments and Ice Cores: The Orbital Tuning Method. Answers Research Journal. 7: 297-309.

* Dr. Hebert is Research Associate at the Institute for Creation Research and received his Ph.D. in physics from the University of Texas at Dallas.

Cite this article: Jake Hebert, Ph.D. 2016. Deep Core Dating and Circular Reasoning. Acts & Facts. 45 (3).