Freshmen in Zhengzhou Institute of Aeronautical Industry Management head bottles of mineral water for upright stand during military training on September 17, 2015 in Zhengzhou, Henan Province of China. More than 6,800 freshmen in the school are required to take part in the military training. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)

The six-months-old female koala cub holds on to the back of zoo keeper Lena at the zoo in Duisburg, Germany, 23 October 2015. The yet unnamed baby weighs 580 grams. (Photo by Roland Weihrauch/EPA)

In 1949, LIFE magazine sent famed photographer Nina Leen to document the daily life of a sassy troupe of young women who had run off and joined the famous Barnum & Bailey Circus in Sarasota, Fla. What developed was a portrait of a sisterhood formed over acrobatics that mixed high-flying wire acts with fashionable high-waisted shorts. Sarasota was once considered “the home of the American circus”. Here: an aerialist smoking while rehearsing for the Ringling Bros. and Barnum & Bailey Circus in Sarasota, FL in 1949. (Photo By Nina Leen/Time Life Pictures/Getty Images)

A man jumps over a puddle outside Victoria Station, as heavy rain falls, in London, Monday June 20, 2016. Monday marks the Summer Solstice – the longest day of the year and the astronomical change of seasons when days are longest and nights are shortest in the Northern Hemisphere. (Photo by Lauren Hurley/PA Wire via AP Photo)

A French farmer leads her cow through the livestock area as preparations continue on the eve of the opening of the International Agricultural Show in Paris, France, February 26, 2016. The Paris Farm Show runs from February 27 to March 6, 2016. (Photo by Benoit Tessier/Reuters)

A students with her face smeared in coloured powder, celebrates Holi at a university campus in Chandigarh, India March 23, 2016. (Photo by Ajay Verma/Reuters)

In this January 27, 2015 photo, penguins walk on the shore of Bahia Almirantazgo in Antarctica. Antarctica “is big and it's changing and it affects the rest of the planet and we can't afford to ignore what's going on down there”, said David Vaughan, science director of the British Antarctic Survey. (Photo by Natacha Pisarenko/AP Photo)

Fireworks explode over a floating Christmas tree in Lagoa Lake in Rio de Janeiro. (Photo by Victor R. Caivano/Associated Press)