In this May 4, 2014 photo, a miner holds an amalgam of mercury and gold he mined after working a 28-hour shift at an illegal gold mining process, in La Pampa, in Peru's Madre de Dios region. Thousands of artisanal gold miners sweat through the long shifts and endure, for a few grams of gold, the perils of collapsing earth, limb-crushing machinery and the toxic mercury used to bind gold flecks. (Photo by Rodrigo Abd/AP Photo)

A pro-democracy demonstrator fights with a Soviet soldier on top of a tank parked in front of the Russian Federation building on August 19, 1991, after a coup toppled Soviet President Mikhail Gorbachev. The same day, thousands in Moscow, Leningrad, and other cities answered Russian Republic President Boris Yeltsin's call to raise barricades against tanks and troops. (Dima Tanin/AFP/Getty Images)

A white whale wears a wreath at the Hakkeijima Sea Paradise aquarium-amusement park complex in Yokohama, Japan, on October 3, 2012. (Photo by Associated Press)

A poster for the IMAX presentation of “The Hunger Games: Catching Fire” (left), and a teaser poster for “The Hunger Games: Mockingjay, Part I”, both created by the Los Angeles-based design firm IGNITION. Both are nominated for the 2014 Key Art Awards in the category of Theatrical Domestic One-Sheet. The Hollywood Reporter's annual competition for the best in film and TV advertising honors some of the most creative imagery used in movie posters. Here is a selection of some of this year's nominees. (Photo by Key Art Awards 2014)

“Hippo Chase”. As we approached the camp the Selinda Reserve of northern Botswana our boat passed by a hippo resting in the water. I turned around to look back at the boat's wake and saw the hippo charging after us! The hippo must've been tired from an all-nighter because he was angry. He rose way up out of the water three times trying to chase our boat! He was coming at us with such force that he created a wake of his own. Photo location: Selinda Reserve of northern Botswana. (Photo and caption by Curtis Simmons/National Geographic Photo Contest)

A man exercises in the early morning on a hilltop overlooking Kabul, Afghanistan March 3, 2016. (Photo by Mohammad Ismail/Reuters)

A member of the Edo Firemanship Preservation Association displays his balancing skills atop bamboo ladder during a New Year presentation by the fire brigade in Tokyo January 6, 2015. (Photo by Thomas Peter/Reuters)

In this Friday, February 6, 2015 photo, sandhill cranes begin to stir after resting for the night at a roosting location along their winter migration route in Cecilia, Ky. According to counts made by biologists with the Kentucky Fish and Wildlife Resources, about 12,000 of the birds have stopped in Cecilia this week during their winter northward migration on their way to their nesting grounds in the Great Lakes region. (Photo by David Stephenson/AP Photo)