Mural of Frida Kahlo on an apartment building near the Biblioteca Vasconcelos in Mexico City, Mexico (© Jessica Sample/Gallery Stock)

A blue tit among daffodils on St David's Day in Blaenpennal, Aberystwyth (© Philip Jones/Alamy Stock Photo)

Volcano Llaima with Araucarias trees in the foreground, Conguillio National Park, Chile (© Fotografías Jorge León Cabello/Getty Images)

Two female lions in the forest surrounding Lake Nakuru, Kenya (© Scott Davis/Tandem Stills + Motion)

Old world swallowtail caterpillar for World Book Day (© ardea.com/Mary Evans/Tonci/Pantheon/SuperStock)

Mineral-laden water in the Rio Tinto in Minas de Rio Tinto mining area, Huelva province, Andalusia, Spain (© David Santiago Garcia/Getty Images)

Komodo National Park, Labuan Bajo, Flores, Indonesia (© Thrithot/Adobe Stock)

Great blue herons in the Wakodahatchee Wetlands, Delray Beach, Florida, USA (© Marie Hickman/Getty Images)

Foothills of the Diablo Range near San Jose, California, USA (© Jeff Lewis/Tandem Stills + Motion)

Onkaparinga River, Port Noarlunga, South Australia (© plainpicture/AWL/Marco Bottigelli)

Thor's Well at Cape Perpetua on the coast of Oregon, USA (© Cavan Images/Offset by Shutterstock)

A balloon flies over the Pyramid of the Sun at sunrise in Teotihuacan, Mexico (© Marco Ugarte/AP Photo)

Common rhododendrons in Semper Forest Park, Ruegen, Germany (© Sandra Bartocha/Minden Pictures)

Mallard, Anas platyrhynchos, mother leading ducklings across road, Arundel, Sussex (© David Tipling/Universal Images Group via Getty Images)

Almond blossoms in Central Valley, California, USA (© Jeffrey Lewis/Tandem Stills + Motion)

Giant panda cub in Bifengxia Panda Base, Sichuan, China (© Suzi Eszterhas/Minden Pictures)

Inisheer, the smallest of the three Aran Islands in Galway Bay, Ireland (© Chris Hill/Minden Pictures)

Mount Etna erupting in 2013, Sicily, Italy (© Wead/Alamy Live News)

Aerial view of the City of Adelaide shipwreck, Magnetic Island, Queensland, Australia (© Amazing Aerial Agency/Offset by Shutterstock)

Sundial on Parnidis Dune, Curonian Spit, in Lithuania (© amoklv/Getty Images)

Bluebell flowers carpet the Hallerbos forest floor, Flanders, Belgium (© Jason Langley/plainpicture)

Lake Hintersee surrounded by mountains, Berchtesgaden, Bavaria, Germany (© Offset by Shutterstock)

Satellite image of the Mania River in Madagascar (© Nasa Earth Observatory image by Joshua Stevens, using Landsat data from the US Geological Survey)

Humpback whale mother pushes her sleeping calf to surface, Maui, Hawaii, USA (© Ralph Pace/Minden Pictures)

The Lagangarbh hut nestles in the valley beneath Buachaille Etive Mòr, Glencoe (© Sophia Spurgin Photography/iStock/Getty Images Plus)

Cradle Mountain-Lake St Clair National Park, Tasmania, Australia (© Paparwin Tanupatarachai/Getty Images)

Mountain hare running across snow-covered upland, Scottish Highlands (© SCOTLAND: The Big Picture/Minden Pictures)

Lyon astronomical clock, Lyon, France (© kyolshin/Alamy)

Detail of an ostrich fern in spring, Washington, USA (© Stephen Matera/Tandem Stills + Motion)

Wayag Island at Raja Ampat, Indonesia (© Amazing Aerial Agency/Offset by Shutterstock)

Elephant (Loxodonta laprofolis) in stealth stance, Marakele National Park, Limpopo, South Africa (© Staffan Widstrand/Minden Pictures)