Radioactive dating technology
Methods fall into one of two categories: relative or absolute.
The probability of a parent atom decaying in a fixed period of time is always the same for all atoms of that type regardless of temperature, pressure, or chemical conditions. The time required for one-half of any original number of parent atoms to decay is the half-life, which is related to the decay constant by a simple mathematical formula.The good dates are confirmed using at least two different methods, ideally involving multiple independent labs for each method to cross-check results.Sometimes only one method is possible, reducing the confidence researchers have in the results. “They’re based on ‘it’s that old because I say so,’ a popular approach by some of my older colleagues,” says Shea, laughing, “though I find I like it myself as I get more gray hair.” Kidding aside, dating a find is crucial for understanding its significance and relation to other fossils or artifacts. Its crust is continually being created, modified, and destroyed.As a result, rocks that record its earliest history have not been found and probably no longer exist.A submethod within biostratigraphy is faunal association: Sometimes researchers can determine a rough age for a fossil based on established ages of other fauna from the same layer — especially microfauna, which evolve faster, creating shorter spans in the fossil record for each species.
Paleomagnetism: Earth’s magnetic polarity flip-flops about every 100,000 to 600,000 years.
Radioactivity was discovered in 1896 by French physicist Henri Becquerel.
By 1907 study of the decay products of uranium (lead and intermediate radioactive elements that decay to lead) demonstrated to B. Boltwood that the lead/uranium ratio in uranium minerals increased with geologic age and might provide a geological dating tool.
They then use that absolute date to establish a relative age for fossils and artifacts in relation to that layer. Anything below the Taupo tephra is earlier than 232; anything above it is later.
For example, New Zealand’s massive Taupo volcano erupted in A. Relative chronology: Researchers have often constructed timelines of a culture or civilization based on the stylistic evolution of its decorative or dramatic arts — that’s why the method is also sometimes called stylistic seriation.
All rocks and minerals contain long-lived radioactive elements that were incorporated into Earth when the Solar System formed.