A thunderstorm rolls across Theodore Roosevelt National Park in North Dakota (© Judith Zimmerman/Danita Delimont)

Reflections on Crummock Water in the Lake District, Cumbria, England (© Damian Harrison/Alamy)

Reflections on Crummock Water in the Lake District, Cumbria, England (© Damian Harrison/Alamy)

Swift fox pups in Grasslands National Park near Val Marie in Saskatchewan, Canada (© John E Marriott/age fotostock)

Swift fox pups in Grasslands National Park near Val Marie in Saskatchewan, Canada (© John E Marriott/age fotostock)

Kayaker exploring sandstone sea caves in Apostle Islands National Lakeshore near Bayfield, Wisconsin (© Chuck Haney/Danita Delimont)

White storks at Los Barruecos Natural Monument, Cáceres, Spain (© Wild Wonders of Europe/Widstrand/Minden Pictures)

Male leopard in Linyanti Wildlife Reserve, Botswana (© Karine Aigner/Tandem Stills + Motion)

Male leopard in Linyanti Wildlife Reserve, Botswana (© Karine Aigner/Tandem Stills + Motion)

Aspen trees in Kluane National Park and Reserve, Yukon, Canada (© Don Paulson/Jaynes Gallery/Danita Delimont)

Triana Bridge over Guadalquivir River, Seville, Spain (© Zu Sanchez Photography/Getty Images)

Elephants in Amboseli National Park, Kenya (© Adam Bannister/Offset)

Mars Express image of the icy cap at Mars’ south pole (© ESA/DLR/FU Berlin/Bill Dunford)

Male and female Ecuadorian horned anoles in Mindo, Ecuador (© James Christensen/Minden Pictures)

Smögen, Sweden (© Martin Wahlborg/Getty Images Plus)

Yukon River viewed from the Midnight Dome, Dawson City, Yukon, Canada (© Robert Postma/Getty Images)

Honey bees drinking nectar from flowers (© Angela Parker/Offset)

Cave interior at Magdalen Islands, Quebec, Canada (© Virginie Fréchette/Getty Images)

Lake Schliersee, Bavaria, Germany (© Rüdiger Hess/geo-select FotoArt)

Wildebeest herd crossing the Mara River between Kenya and Tanzania (© zhengvision/Getty Images)

Wildebeest herd crossing the Mara River between Kenya and Tanzania (© zhengvision/Getty Images)

Dubai Fountain in the Burj Lake, taken from the Burj Khalifa, Dubai, UAE (© Eli Asenova/Getty Images)

Farmland in Washington state's Palouse region (© Art Wolfe/Getty Images)

Brown bears in Katmai National Park and Preserve, Alaska (© imageBROKER/SuperStock)

Winnats Pass in the Peak District of Derbyshire, England (© Christopher Drabble/Alamy)

Anak Krakatoa volcano erupting off the coast of Sumatra, Indonesia (© Martin Rietze/Alamy)

Jeep trail in Ranthambore National Park, India (© Lewis Kemper/Alamy Stock Photo)

The Gardens of the Palazzo Corsini al Prato in Florence, Italy (© Will Perrett/Alamy)

Hardee County Fair in Wauchula, Florida (© Oscar G. Davila/Getty Images)

Neuwerk Island seen from Cuxhaven, Lower Saxony, Germany (© Michael Dittel/EyeEm/Getty Images)

Slacklining between giant boulders in Bishop, California (© Evgeny Vasenev/Aurora Photos)