Dating fingerprint cases
In October 2000, a pair of duck hunters in Utah stumbled into a murder mystery.
As they walked along the south shore of the Great Salt Lake—just 100 feet from Interstate 80—they found buried in a shallow grave a plastic bag containing a white sock, an oversized t-shirt, a woven blue choker necklace, 12 bones, and a human skull. Police gathered what clues they could from the remains of "Saltair Sally," named after a resort near where her remains were found, though there wasn't much to go on.
"It was our first case, where we really got started," says Chesson, an analytical chemist. " Such clues would give investigators valuable information as they continued to search for the victim's identity.
"They contacted us to see if we would analyze the hair—a long length of the hair—looking at hydrogen and oxygen to see, Was she local? To see how that's possible, let's follow a raindrop from a cloud over the Pacific Ocean to Saltair Sally's strand of hair.
When those clouds rain, the heavier, oxygen-18 containing water molecules will fall out first. As the rain cloud moves inland, it's constantly losing molecules with oxygen-18, and its raindrops become isotopically lighter and lighter.
Since our drinking water comes from rainwater, people near the coasts drink water with more oxygen-18 atoms in it than people living inland.
Those atoms eventually become a part of our tissues, like hair.