How do scientists know how old an object or human remains are?
Additional complications come from the burning of fossil fuels such as coal and oil, and from the above-ground nuclear tests done in the 1950s and 1960s.
Along with hydrogen, nitrogen, oxygen, phosphorus, and sulfur, carbon is a building block of biochemical molecules ranging from fats, proteins, and carbohydrates to active substances such as hormones.
All carbon atoms have a nucleus containing six protons.
At an archaeological dig, a piece of wooden tool is unearthed and the archaeologist finds it to be 5,000 years old.
A child mummy is found high in the Andes and the archaeologist says the child lived more than 2,000 years ago.