Investigations into ancient history, particularly its chronology, are increasingly relying on scientific data. Although that trend is a positive development, caution is warranted. This post considers one of four types of scientific data that can be inaccurate: radiocarbon dates.
Many factors can cause radiocarbon dates to be inaccurate. The “International” Calibration Curve works best under certain circumstances that are common across much of the Northern Hemisphere: low-elevation forested areas that are relatively distant from large water bodies, tectonic plate boundaries, and volcanic outgassing. Many locations lack these characteristics. For example, radiocarbon-dated materials from near-shore areas typically appear older than they are because of outgassed carbon dioxide from oceans and seas. Some conditions can worsen that offset, including 1) upwelling currents nearby and 2) a tectonic plate boundary offshore.
Laboratory reports often provide the age of the sample as a figure in uncalibrated years (years BP, i.e., before 1950) with an associated error range. For example, a 2σ measurement of 3352±20 means 3352 BP with plus or minus 20 years within two standard deviations (or a supposed 95% probability of accuracy). If an uncalibrated date has more than one intersection on the calibration curve, the picture is complicated with multiple ranges of calibrated dates (in years BCE). But even if that is not the case, far more radiocarbon measurement ranges do not include the actual sample ages than implied by the claimed 95% probability of accuracy. In fact, in many areas of the Middle East, inaccurate radiocarbon dates are more prevalent than accurate ones. The reason is that neither the archaeologists collecting the samples nor the technicians performing the measurements have considered regional offsets. What causes these variations?
Carbon dioxide is only about 0.04% of the total atmospheric gases, and the number of CO2 molecules containing carbon-14 is fewer than one out of a trillion! Consequently, the introduction of extraneous carbon dioxide with enriched or deficient carbon-14 levels can cause significant variations of that isotope in organic materials. Higher regional levels of carbon-14 are a rare circumstance, but subnormal quantities are quite common.
As we have seen regarding Nile Valley measured radiocarbon dates, they can range from over a century too young to over a century too old. The circumstances there are unique, i.e., the deposition of organic material from the tropics in southern Egypt and the accumulation of centuries-old Nile silt in the north. This unusual situation influences Levantine carbon dates:
Ordinarily, the lower quantities of CO2 containing carbon-14 in seawater can impact the amount of the isotope incorporated into organic matter in nearby land areas. The average apparent difference in radiocarbon ages between contemporaneous land and sea samples is approximately 400 years. Thus, the wind passing over a water body picks up CO2 that is deficient in carbon-14. Consequently, downwind from the sea will typically have organic matter that appears to be older than it is. However, the opposite is true in the southern Levant. Why?
Before the damming of the Nile River, its annual flooding brought organic matter from the tropics. The river deposited much of that silt in Upper Egypt, but the Nile carried some of it all the way to the Mediterranean Sea. The sea’s counter-clockwise circulating water then carried that silt toward the east and northward. When microorganisms fed on the organic material, carbon-14-enriched CO2 bubbled up, and winds blew it into the southern Levant. This circumstance causes an average positive offset of around half a century (making radiocarbon dates younger than the actual ages).
Nevertheless, in most cases of regional variations, the offset is in the opposite direction. The Jordon Rift Valley constantly outgasses “dead carbon dioxide” that is utterly devoid of carbon-14. Thus, radiocarbon-dated materials, especially from near the Dead Sea, appear to be much older than their actual ages. The same is true of other locations across the Middle East that are near tectonic plate boundaries. Many of the so-called ‘most ancient sites’ are in such places or near volcanic outgassing.
Finally, radiocarbon-dated bones found in carbonaceous caves often have fantastically ancient radiocarbon ages. Since those bones have spent many millennia surrounded by limestone, are they not contaminated by microorganisms that incorporate old carbon into the bones? Technicians attempt to remove it during pretreatment, but this process is imperfect, often rendering such radiocarbon dates entirely unreliable.
See this author’s forthcoming free e-book, Scientific Explanations for Radiocarbon Offsets at Astronomically Dated Sites.
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