TOEFL: Read an Academic Passage
TOEFL: Read an Academic Passage Instructions: Read the following academic passage. Then answer the questions that follow. Choose the best answer to each question based on the information in the passage. Radiocarbon Dating Radiocarbon dating, developed in the late 1940s by physicist Willard Libby, revolutionized archaeology by providing a reliable method for determining the age of organic materials. The technique relies on the fact that all living organisms absorb carbon from their environment, including a small amount of radioactive carbon-14, alongside the far more abundant stable carbon-12. While an organism is alive, the ratio of carbon-14 to carbon-12 in its tissues remains roughly constant, because it continuously exchanges carbon with its surroundings. Upon death, however, this exchange stops, and the carbon-14 begins to decay at a known rate - its half-life is approximately 5,730 years. By measuring the remaining carbon-14 in a sample and comparing it to the expected initial level, scientists can estimate how long ago the organism died. The method is most effective for materials up to about 50,000 years old; beyond that, too little carbon-14 remains to produce accurate results. One limitation is that radiocarbon dating applies only to organic materials - wood, bone, charcoal, leather - and cannot directly date stone tools or metal artifacts. Furthermore, fluctuations in atmospheric carbon-14 levels over millennia mean that raw radiocarbon dates require calibration against records from tree rings and other sources to yield accurate calendar ages.