Throughout our lives, we repurpose atoms that previously belonged to other animals, plants, soil, or bacteria, atoms that were created in the Big Bang or by stellar fusion. A carbon-dating study in 2005 found that the average cell in the adult human body is only seven years old. Though some cells stay with us pretty much our whole life, skin cells are on average replaced every two weeks, and others (like red blood cells) are replaced every couple of months.
