Can radioactivity be used as a clock?

All radioactive elements spontaneously decay into daughter elements. Decay rates vary among the different radioactive elements at what appears to be a constant rate for each radioactive element as measured by extensive testing over the last 125 years. Scientists have tried to change the decay rates by various means with limited minor success. These apparent constant rates led to the idea that radioactivity could be used as a clock.

Theoretically for this “clock” to date a sample, all that is needed is the present ratio of daughter atoms derived from the original parent atoms in the sample to the original parent atoms in sample and the constant decay rate for the radioactive element. Modern equipment such as AMS in laboratories under the direction of PhD scientists can measure very accurately the present amounts of the parent and daughter atoms in a sample.

To use radioactivity as a clock, all three of the following requirements must be met:

Constant Rate – The rate of decay must be constant over the whole period under investigation.

Initial Conditions - Initial ratio of daughter to its parent must be known.

Closed System – There must be no migration in or out of parent or daughter isotopes.

Major problems with radioactive dating are the uncertainties surrounding meeting the above clock requirements. Long half-life radioactive dating is only theoretical because no human observer was there to record the initial conditions, or whether decay rates were constant, or whether the system was continuously closed. The void from the lack of data has been filled in by questionable assumptions.

As mentioned previously, constant decay rates for the various radioisotopes have only been measured for the last 125 years. Extrapolating present decay rates back for even thousands of years is far beyond the small extrapolations normally considered reasonable in science. Evidence from an eight-year long research project under the acronym RATE (e.g., helium diffusion in zircons, Carbon-14 in diamonds, Carbon-14 in coal, radiohaloes in granite, etc.) apparently indicates that rates of decay for radioactive isotopes have been greatly accelerated in the past. [1] (a) Without a constant rate of decay, no radioactive clock is possible.

Initial daughter elements in the sample will result in ages that can be many orders of magnitude older than actual. To correct this, the isochron plot concept was proposed to theoretically remove the excess daughter elements. Details of the Isochron method are discussed in many sources widely available so they will not be discussed here. Although Isochron plots may correct for initial daughter elements, they also reveal another major problem. The isochrons in many cases are hundreds of millions to billions of years off when compared to known dates for the samples. For example, the andesite lava from the 1949, 1954, and 1955 eruptions of Mt. Ngauruhoe in New Zealand dated around 133, 197, and 3,908 million years old for the Rb-Sr, Sm-Nd and Pb-Pb isochrons, respectively. [2] [3] (b)    

Finding rock samples that were in a closed system for long-life radioactive isotopes is problematic. For instance, uranium and lead are easily moved in and out of samples with water.

Using Carbon-14 (14C) with a half-life of about 5,730 years as a clock also has its problems. Carbon-14 is created in the upper atmosphere when cosmic rays impact Nitrogen-14. The small amount of Carbon-14 thus created then combines with oxygen in the atmosphere to form 14CO2 and is mixed with the large amount of 12CO2 in atmosphere. This mixture of 14CO2and 12CO2 is then taken into plants by photosynthesis and into animals by eating plants. When living organisms die carbon ceases to be added to the remains. So, the 14C/12C ratio in the atmosphere at death is the initial condition. This initial 14C/12C ratio works well for recently dead organisms where the atmospheric 14C/12C ratio has been measured. It is a different story for very ancient organisms where the atmospheric 14C/12C ratio can only be assumed.

Because 14C’s half-life is so short, it decays beyond detection in samples older than around 90,000 to 100,000 years. Samples of dinosaur bones that are conventionally dated at 65 million years or older have been dated by the radiocarbon clock at less than 40,000 radiocarbon years. [4] Samples obtained for the RATE project from Eocene, Cretaceous, and Pennsylvania coal deposits conventionally dated between 56 to 318 million years old are all dated by the radiocarbon “clock” at around 50,000 radiocarbon years. [5] [6] (c) (d)



    1.       Long-life radioisotopes can be used as a clock only for recent events providing the initial conditions are known and it is a closed system.

    2.        Carbon-14 can be used as a clock to date recent organic remains, but its accuracy is uncertain for older organic remains because of uncertainty in the initial conditions and the possibility of accelerated decay.

    3.        All organic remains where Carbon-14 is detected cannot be older than 90,000 to 100,000 years.


(a)  RATE is an acronym for Radioisotopes and the Age of the Earth. This project was sponsored by the Institute for Creation Research. The RATE scientists included two geologists, a geophysicist, three physicists, and a meteorologist, all with earned doctorates. [7]

(b)  Nine other examples may be found in references [2] and [3]

(c) RATE had ten coal samples tested: three Cenozoic, three Mesozoic, and four Paleozoic [8] [9]

(d) These radiocarbon years are based on a conventional calibration curve. The actual age may be much younger.


{a} Triceratops mounted skeleton at Los Angeles Museum of Natural History, Los Angeles, United States of America. Source: Allie Caulfield Derivative: User:MakerKnight, CC BY-SA 3.0, via Wikimedia Commons.


[1] DeYoung, D., Thousands...Not Billions, (Green Forest, AR: Master Books, 2005)

[2] Morris, J., The Young Earth, (Green Forest, AR: Master Books, 1994, 2007), 57

[3] DeYoung, D., 126-127

[4] Carbon-14-dated dinosaur bones are less than 40,000 years old, New Geology US, viewed on the internet May 5, 2021

[5] Baumgardner, John, Carbon Dating Undercuts Evolution's Long Ages, Acts & Facts. 32 (10), 2003, 

[6] Snelling, A., Earth’s Catastrophic Past, Volume 2, (Dallas, TX: The Institute for Creation Research, 2009), 860-861    

[7] DeYoung, D., 18

[8] DeYoung, D., 54

[9] Snelling, A., 860