Round balls of rock, known as concretions, have washed up on Canada’s Arctic shoreline.
The strange concretion phenomenon is common, but take millions of years to form.
Concretions are found across areas of Kodiak Island on Alaska’s southern coast and Qeqertarsuaq in Greenland.
According to Geologist Survey of Canada researcher Marc St-Onge, the strange rock formations are formed when a pile of sediment made from mud, silt or sand is located near a flowing body of water.
Other harder materials found in bodies of water, such as shells, leaves and fossils, are then pushed into the sediment pile through the flowing water.
The spheres are formed when a “cementing mineral” dissolves in the sediment pile, such as calcite which forms limestone.
For millennia, layers of concrete-like rock form on top of the pile – with the outer layers being softer and easier to erode.
But to form a perfect sphere, Onge estimated it takes millions of years from the impacts of waves and ice.