A cenote is a natural phenomenon, a sinkhole in the Earth’s surface. The Yucatan Peninsula in Mexico has an estimated 7,000 cenotes because it is primarily made up of porous limestone. For millions of years, rainfall slowly ate away at the limestone and a huge system of underground caves and caverns was formed. Many filled with water from rain or from the underground water table. When the roof of a water filled cave collapses, a cenote is born. The water found in a cenote may be fresh water, salt water, or both. Structurally it may be completely open, like a lake, almost completely closed with just a small opening at the top, or somewhere in between.

A fisherman caught a record-breaking 805lb Mako shark – and then barbecued and ate it with his friends. Joey Polk, 29, and his two cousins Earnie Polk, 43, and Kenny Peterson, 21, battled the 11ft predator for more than an hour before finally hauling it onto the beach. They normally tag and release their catches for conservation but were unable to resuscitate this one and instead made it the main course at a jumbo-sized family barbecue. (Photo by Joey Polk/Barcroft Media)

The Greenland ice sheet is a vast body of ice covering 660,235 sq miles, roughly 80% of the surface of Greenland. It is the second largest ice body in the world, after the Antarctic Ice Sheet. Some scientists predict that climate change may be near a "tipping point" where the entire ice sheet will melt in about 2000 years. If the entire 2,850,000 cubic kilometres (683,751 cu mi) of ice were to melt, it would lead to a global sea level rise of 7.2 m (23.6 ft).

Alex Sun, left, Peter Simplicio and Matt Connelly jump through a hole in the ice into Lake Andrews on the Bates College campus, Friday, February 9, 2024, in Lewiston, Maine. The annual Bates College Puddle jump started 50 years ago as a Winter Carnival tradition. (Photo by Andree Kehn/AP Photo)

Cast member Dan Stevens points at Kathryn Newton's heels as they attend a premiere for the film “Abigail” in Los Angeles, California on April 18, 2024. (Photo by Mario Anzuoni/Reuters)

American model Kaia Gerber (L) and American actress Kate Hudson attend the “Shell” After Party during the Toronto International Film Festival at Elevation Pictures on September 13, 2024. In this dark comedy and body horror about society's obsession with youth and good looks, an actress (Elisabeth Moss) challenges a beauty firm CEO (Kate Hudson) over her company's questionable science. (Photo by ZUMAPRESS.com/The Mega Agency)

Loreen from Sweden performs after winning the 2023 Eurovision Song Contest in Liverpool, Britain on May 14, 2023. (Photo by Phil Noble/Reuters)

A woman jumps over a puddle of rainwater in north London on August 2, 2023. Met Office has issued a yellow severe weather weather for heavy downpours, strong winds and thunderstorms throughout today in London, and in many other parts of England and Wales. (Photo by Dinendra Haria/London News Pictures)