Tourists take a “selfie” as demonstrators burn a trash container during a May Day rally in Barcelona, Spain, on May 1, 2014. Tens of thousands of workers marked May Day in European cities with a mix of anger and gloom over austerity measures imposed by leaders trying to contain the eurozone's intractable debt crisis. (Photo by Manu Fernandez/Associated Press)

Children are engulfed by foam during the Bubble Show event in Beijing, China, Sunday, June 26, 2016. Thousands of residents enjoy colored foam churned out by machines along a running track at the event designed for children and parents' interaction. (Photo by Ng Han Guan/AP Photo)

Rescue workers try to pull out a piece of an exploded Grad missile outside an apartment building in Vostochniy district of Mariupol, Eastern Ukraine, Sunday, January 25, 2015. Indiscriminate rocket fire slammed into a market, schools, homes and shops Saturday in Ukraine's southeastern city of Mariupol, killing at least 30 people, authorities said. The Ukrainian president called the blitz a terrorist attack and NATO and the U.S. demanded that Russia stop supporting the rebels. (Photo by Evgeniy Maloletka/AP Photo)

NASA astronaut Reid Wiseman and European Space Agency astronaut Alexander Gerst (not shown) works outside the space station's Quest airlock in the first of three spacewalks for the Expedition 41 crew aboard the International Space Station in this NASA image released October 8, 2014. (Photo by Reuters/NASA)

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

A worker inspects the Christ the Redeemer statue which was damaged during lightning storms in Rio de Janeiro January 21, 2014. (Photo by Severino Silva/Reuters/Agência o Dia)

A file photograph dated 07 January 2006 and released by Greenpeace, showing the Yushin Maru, a factory ship in a Japanese whaling fleet, injuring a whale with it's first harpoon attempt. A UN court in The Hague on 31 March 2014 halted Japan's much-criticized whaling programme, ruling that it contravenes a 1986 moratorium on whale hunting. Japan must end its 'research whaling' programme, the International Court of Justice (ICJ) said. Japan said the programme was for scientific research and permitted under international conventions. Australia had brought the case to the ICJ in 2010, charging that Japan was breaching international law by killing hundreds of whales every year for commercial purposes. Japan was “deeply disappointed” by the ruling, an unnamed government official was quoted by the Kyodo News agency as saying. But the official said Japan would stand by the ruling. (Photo by Kate Davison/EPA)

Merit Prize Winner: “A Well Earned Rest in the Sahara”. This photo of Moussa Macher, our Tuareg guide, was taken at the summit of Tin-Merzouga, the largest dune (or erg) in the Tadrat region of the Sahara desert in southern Algeria. Moussa rested while waiting for us to finish our 45-minute struggle to the top. It only took ten minutes of rolling, running, and jumping to get back down. The Tadrat is part of the Tassili N'Ajjer National Park World Heritage area, famous for its red sand and engravings and rock paintings of cattle, elephants, giraffes, and rhinos that lived there when the climate was milder. Photo location: Summit of Tin-Merzouga, Tadrat, Tassili N'Ajjer National Park, Algeria. (Photo and caption by Evan Cole/National Geographic Photo Contest)