The most common isotopes of carbon are carbon-12 and carbon-14. Carbon-12 is the most abundant isotope, making up about 98.9% of naturally occurring carbon, and is stable. Carbon-14, on the other hand, is radioactive and is used in radiocarbon dating to determine the age of archaeological and geological samples. Both isotopes are crucial in various scientific fields, including biology, geology, and archaeology, providing insights into life processes and environmental changes over time.