Some living things are very, very old. In the mountains of California, there is a pine tree that is about 4,800 years old. It started growing before the Great Pyramid in Egypt was built.

Its location is a secret to protect it. In the cold sea, Greenland sharks may live for almost 400 years. A clam from the sea near Iceland was 507 years old.

Some living things have survived for an astonishing length of time. A bristlecone pine called Methuselah, in California's White Mountains, was found in 1957 to be about 4,790 years old, so it is now over 4,800.

Scientists count tree rings by taking a thin sample from the trunk, so the tree does not have to be cut down. In 2016, Danish researchers estimated the age of Greenland sharks by studying the center of their eye lenses. The largest female was about 390 years old, although the margin of error was 120 years. A clam collected near Iceland was found to be 507 years old by counting growth lines on its shell.

Earth's oldest organisms put human history in perspective. In California's White Mountains, a bristlecone pine known as Methuselah was dated in 1957 at roughly 4,790 years by counting rings in a thin core, making it older than the Great Pyramid. Its exact location is kept secret to protect it. These trees grow extremely slowly in cold, dry conditions, producing dense, decay-resistant wood, and can survive even when most of the trunk has died.

Some animals also reach great ages. In 2016, Nielsen and colleagues used radiocarbon in the center of the eye lens, which forms before birth and is never replaced, to estimate the ages of Greenland sharks; the largest of 28 animals was about 390 years old. The uncertainty, however, was 120 years either way, so the true figure could be as low as 272.

By contrast, the 507-year age of an Icelandic clam came from counting shell growth lines, a more precise method. Age is even harder to define for clonal organisms, such as a seagrass in Australia's Shark Bay that may have spread for up to 4,500 years, because the age refers to the genetic individual rather than any single shoot.