When did humans start wearing shoes?

Scientists have discovered many ancient shoes around the world, including 5,500-year-old leather shoes in Armenia, 6,200-year-old grass sandals in Spain, and footwear as old as 8,300 years old in Missouri.

But when did humans actually invent shoes? That's tricky to answer because the animal skins, plant fibers and other materials used to make shoes tend to break down over time. The oldest known shoes are more than 10,000 years old, but our ancestors may have worn them much earlier than that, fossilized footprints suggest.

The oldest shoes that researchers have directly dated are a pair of 10,400-year-old sandals recovered from Fort Rock Cave in central Oregon, according to Thomas Connolly, archaeological research director at the University of Oregon's Museum of Natural and Cultural History.

Archaeologists who began excavating at Fort Rock Cave in 1938 discovered dozens of sandals woven from sagebrush bark and other fibers. Similar footwear has been found at nearly a dozen sites in the northern and western Great Basin, the arid U.S. region between the Sierra Nevada and the Rocky Mountains, Connolly explained. "Generally, these are finely made, with a flat sole and foot cover," he told Live Science.

Related: 12 old shoes found in archaeological excavations from around the world

Scientists who interviewed Native groups in the Oregon area, such as the Klamath and Northern Paiute peoples, found that "in historic times, woven footwear was for winter use, especially for work around cold marshes and lakes where one might retrieve fishing or fowling nets, or harvest bulrushes for mats and baskets," Connolly said.

Although these sandals are porous, their fibers would have retained body heat to keep feet warm, even when they were soaked in water. "Ethnographer Samuel Barrett was told by his Klamath informants that woven shoes were worn so that 'one might in the dead of winter walk with comparative comfort through marshes where the water is extremely cold,'" Connolly said.