Eighteenth-century French naturalist Benoit de Maillet attempted to estimate Earth’s age based on its physical properties. Noting that seashells could be found in sediments on land in many places around the world de Maillet reasoned that Earth’s surface must have once been entirely covered by water and, that sea levels have been falling steadily ever since. By observing sea levels and estimating how fast they fellde Maillet thought he could calculate how long Earth had existed Although de Maillet’s main idea was flawed-sea levels have remained roughly constant for billions of years-he correctly realized that long-term natural processes could provide a way to measure Earth’s age and his suggestion that Earth could be as old as 2 billion years was daring and prescient.