Sometimes referred to as "carbon dating" or "carbon-14 dating." Carbon 14 is a weak radioactive isotope of the element carbon formed by the interaction of cosmic rays and atmospheric nitrogen. Plants absorb small doses of it during photosynthesis, and animals acquire it by eating plants or plant-eating animals. When the organism containing carbon 14 dies the isotope begins to decay at a regular rate, and scientists can use this to determine the age of the plant or animal in question. Because of carbon 14's relatively short half-life, its dating accuracy is good to only about 50,000 years.
A periodic reversal of the normal flow of currents in the Pacific, greatly altering weather patterns.
A refuse pile; archaeologists treasure such piles because a great deal can be learned about the material culture of a society by what the people threw out over long periods of time.
A continuous spine of mountain ranges near or along the entire western coast of the Americas.
Cold period with near Ice Age temperatures; name derived from a white blooming plant flourishing during the period, itself named for a Greek mythological nymph.
Spanish for Quechua khipu; the knots in the strings and the varying distances from each other have supposedly numerical or symbolical meanings.
A wild grass native to Mesoamerica, believed to be ancestral to maize (corn).