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Found in rocks throughout Earth's crust, zircons are some of the oldest bits of mineral on Earth. These tiny crystals are so durable—and some are so ancient, dating to just 150 million years or so after our world formed—that geologists have long viewed the tiny bits of minerals embedded within them as a kind of time capsule, offering a peek at conditions on the early Earth. But a new study suggests that these so-called inclusions are not as pristine as scientists thought, raising doubts about conclusions that researchers have drawn from them, from the rise of early oceans to the movements of the ancient continents.