Giant Olympic rings are towed on The River Thames past The Tower of London on February 28, 2012 in London, England. (Photo by Peter Macdiarmid/Getty Images)

Artists watch burning an effigy of Lady Maslenitsa as they celebrate Maslenitsa, or Pancake Week, in Baikonur, Kazakhstan, March 13, 2016. Maslenitsa is widely viewed as a pagan holiday marking the end of winter and is celebrated with pancake eating and shows of strength, while the Orthodox Church considers it as the week of feasting before Lent. (Photo by Shamil Zhumatov/Reuters)

A tourist watches as the moon passing in front of the sun as it approaches a full solar eclipse in the northern Australian city of Cairns November 14, 2012. (Photo by Tim Wimborne/Reuters)

Muslim women light candles during the “EarthHour” in Jakarta, Indonesia, on March 23, 2013. Hundreds of people observed the global event that encourages people to turn off their lights for 60 minutes. (Photo by Dita Alangkara/Associated Press)

The MSC Napoli cargo ship lies in a dry dock at Harland and Wolff ship builders as it is dismantled for recycling on April 11, 2008 in Belfast, Northern Ireland. (Photo by Peter Macdiarmid/Getty Images)

Keith Haubrich of Seattle, Wash., reacts to the crowd while competing in the Dali Moustache division during the fourth annual Just For Men National Beard and Moustache Championships Saturday, September 7, 2013 in New Orleans. Haubrich went on to win the gold medal for the Dali division.Contestants competed in 18 different categories including Dali, full beard natural and sideburns.(Photo by Susan Poag/AP Photo)

Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)