The fourth annual BigPicture Natural World Photography Competition aims to celebrate the diversity of life on Earth, and encourages people to protect and conserve it. Here: “The Salmon Catchers”. Terrestrial Wildlife. To capture this view of a mother grizzly bear and her cub, photographer Peter Mather set up a camera trap on a log that he knew the bears tended to traverse while fishing for salmon, in the Yukon River watershed in Canada. (Photo by Peter Mather/BigPicture Natural World Photography Competition 2017)

In this March 3, 2015 photo, a group of California sea lions rest on a large bouy in the San Ignacio lagoon, in the Pacific Ocean, near Guerrero Negro, in Mexico's Baja California peninsula. (Photo by Dario Lopez-Mills/AP Photo)

A hot air balloon competition called “Grudziadzkie Zawody Balonowe” is held in Lisie Katy, central-northern Poland, 14 May 2021. The compe​tition is held for the eighteenth time. (Photo by Tytus Zmijewski/EPA/EFE)

The sun rises through the thick fog that covers the city of Frankfurt, Germany, Friday, November 12, 2021. (Photo by Michael Probst/AP Photo)

Players in action during the Swamp Soccer Championships 2019 in Hyrynsalmi, Finland, 19 July 2019. The World Championship in swamp football is played annually on Vuorisuo bog in Hyrynsalmi. (Photo by Tomi Hanninen/EPA/EFE)

These beautiful shots may look like works of modern art – but they are actually close-ups of chemical reactions. The works were snapped with the help of a group of scientists from the University of Science and Technology of China (USTC) in Anhui, China. Here: Zinc reacting with lead nitrate in a soft gel to form lead crystals. (Photo by Yan Liang/Caters News)

A sanitation worker fumigates using sodium hypochlorite in an archive room to fight the spread of the coronavirus disease (COVID-19) in the Milimani commercial courts in Nairobi, Kenya, July 17, 2020. (Photo by Baz Ratner/Reuters)

Bollywood actress Chitrashi Rawat lies in a plastic drum as she is briefed by a crew member during the shoot for the film “Black Home” at a beach on the outskirts of Mumbai April 26, 2013. (Photo by Danish Siddiqui/Reuters)