The Fossil Record 83well-understood anomaly. Normal radiocarbon dating works when nitrogen-14 from the
atmosphere is transformed by cosmic radiation into carbon-14, which is then incorporated
into living tissues. When the organism dies, the carbon-14 begins to decay, making the bone,
shell, or wood (or anything bearing carbon) datable, as long as it is less than 80,000 years
old (since the radiocarbon decay rate is relatively fast). These peculiar clams live in water
covering ancient limestone that releases radioactively dead carbon into the water. That
ancient carbon (instead of the normal carbon derived from the atmosphere) then becomes
part of the mollusk shells, where it throws the ratio off. Radiocarbon specialists have long
been aware of this minor problem and never rely on dates where this kind of contamination
could be an issue.
Nearly every time you read a creationist account of radiometric dating, they find
some way to misuse or misinterpret the system, then accuse the system of being unreli-
able when they have only demonstrated that they are incompetent and have no idea how
it works. Take, for example, the familiar creationist trope about a volcanic lava in Australia
dated at 45 million years old which flowed around trees which were radiocarbon dated at
40,000 years old. They point to this example and say, “Aha, this proves that all radiometric
methods are unreliable.”
So why did the Australian anomaly occur? The thing to remember is that each radioac-
tive “clock” ticks at a different rate, but all of them keep good time (if they are used prop-
erly). Radiocarbon has a very short half-life of 5,370 years, so it decays extremely rapidly. By
40,000 years (some labs can push it to 80,000 years now), it is radiocarbon dead—no more
decay is occurring, and you cannot use it to measure anything anymore. Thus, radiocar-
bon is primarily used by scientists who work on really young events of the last ice age and
Holocene: archeologists and those who work on the last glacial cycle. A real scientist would
never even consider using it for anything older, and any fools who do so show that they have
no clue what they are doing. Other isotopic systems are useful in different age ranges. U-Pb
(both isotopic pairs) and Rb-Sr decays over billions of years, so it is only used on the oldest
earth rocks, plus moon rocks and meteorites. K-Ar is the system used by most geologists,
since it can date rocks as young as 1 million years, and as old as the oldest rocks we have, so
its useful age range covers the vast majority of common geologic settings. To go back to our
clock analogy, radiocarbon is like a clock that ticks really fast and runs down quickly. U-Pb
and Rb-Sr are like a big grandfather clock that ticks very slowly but doesn’t run down except
over a very long time. The Australian trees-in-lava scenario only demonstrates the complete
incompetence of creationists. They cited the K-Ar analysis to date the lava at 45 million years
old, which means that no real geologist would waste their time dating the radiocarbon-dead
trees. But the creationist ran the radiocarbon on them anyway, and sure enough, he got dates
around 40,000—which only means the sample is radiocarbon dead and older than 40,000, not that
the age of the sample is 40,000 years. It’s like looking at the time on a fast-running clock
that has stopped and comparing it with the slow grandfather clock. The creationist says that
since they are different, no clocks can be trusted, when in fact he was foolishly looking at
a clock that has run down and stopped.
Creationists don’t give scientists any credit for being skeptical and self-critical about
their own data. But anyone who deals with geochronology knows that the dates are subject
to constant scrutiny by multiple labs, and anything that is fishy is quickly challenged and
rejected. The result is an extremely robust set of data, where multiple independent radioac-
tive atomic systems (for example, potassium-argon, uranium-lead, and rubidium-strontium)