A varve is a pair of sedimentary layers, a couplet, that are believed to form in an annual cycle as the result of seasonal weather changes. Typically formed in glacial lakes a varve couplet consists of a coarser grained summer layer formed during open-water conditions, and a finer grained winter layer formed from deposition from suspension during a period of winter ice cover. Many varve deposits contain hundreds of couplets.
This dating method involves measuring the number of layers to determine the age for calibrating dating methods like Carbon-14 dating. It is much like counting tree rings and can be used as evidence that young earth creationism is incorrect, since some notable examples, if actually annual, indicate an age of the earth greater than 10,000 years.
Some cases of varve dating that indicates an older earth when accepted as varves include:
- Lake Suigetsu - varve layers under this lake seem to date back to at least 45 ka BP, perhaps even as old as 100 ka BP, according to research done by H. Kitagawa and J. van per Plicht in a 1995-1197 report . Varve deposits from the lake were calibrated using Carbon-14 dating.
- Green River Formation - this formation in Wyoming, USA, is claimed to have millions of layers and therefore represent a timeline extending further back than the young earth view permits.
Such views as represented by evolution actually rely on assumptions that these varves are laid down consistently year after year. In fact when Mount St. Helens erupted in Washington State it produced 25 feet of finely layered sediment in a single afternoon! Other such catastrophic events such as the Flood of Noah could also imply the action of laying down many layers quite rapidly within a year time-frame. Thus even millions of layers could be formed in just a few years.
Furthermore experiments show that the thickness of the layers in a continuous heterogranular deposition is independent of the rate of deposition, but is related to the difference in grain size. So varves are not really a problem for a young earth, they just show that deposition rates were higher during and immediately following the Biblical flood than they are today.
Some secular geologists believe that varves may actually be diurnal, reflecting tides instead of seasonal causes. If this is so, formations like the Elatina Formation in South Australia (which is about 250 meters thick) could be accounted for in a mere 60 years.(Williams & Schmidt p. 21-25)(Horgan p. 11)
- Glossary of Glacial Terminology by the U.S. Geological Survey
- Varves: Problems for Standard Geochronology Creation in the Crossfire
- Don't varves prove that world is older than the Bible says? Q&A by Tas Walker
- Williams, G. & Schmidt, P., 2000. Proterozoic equatorial glaciation: Has ‘snowball Earth’ a snowball’s chance? The Australian Geologist 117, 21-25.
- Horgan , 1989. Blame it on the Moon. Scientific American of Feb p. 11.