Because instruments can fail, controllers can make mistakes, pilots can miss steps on checklists.
In short, because we can all make mistakes or fall victim to our own biases.
Iowa State University physicists, left to right, Pieter Maris and James Vary have used supercomputing power to solve the puzzle of the long, slow decay of carbon-14.
That long half-life makes carbon-14 a useful tool to determine the ages of skeletons and other artifacts.
A cotton T-shirt manufactured and tested in 2050 may appear to be the same age as an artifact from the 11th century when dated using the radiocarbon method.
A new shirt made in 2100, if emissions continue unabated, could appear to come from the year 100, alongside something worn by a Roman soldier.
Radiocarbon dating has been helping put the planet's history in the right order since it was first invented in the 1940s, giving scientists a key way to determine the age of artifacts like the Dead Sea Scrolls and the Shroud of Turin.
The burning of fossil fuels is altering the ratio of carbon in the atmosphere, which may cause objects tested in the coming decades to seem hundreds or thousands of years older than they actually are, according a study published in the Proceedings of the National Academy of Sciences.
Radiocarbon is a radioactive form of carbon that's created when nitrogen reacts with cosmic rays in the upper atmosphere.He said that his team and the laboratories they employed took special care to avoid contamination.That included protecting the samples, avoiding cracked areas in the bones, and meticulous pre-cleaning of the samples with chemicals to remove possible contaminants.Members of the Paleochronology group presented their findings at the 2012 Western Pacific Geophysics Meeting in Singapore, August 13-17, a conference of the American Geophysical Union (AGU) and the Asia Oceania Geosciences Society (AOGS).Since dinosaurs are thought to be over 65 million years old, the news is stunning - and more than some can tolerate.