Tourists kissing front of Malaysia's landmark Petronas Twin Towers with lights on before turned off to mark Earth Hour 2016 in Kuala Lumpur, Malaysia, 19 March 2016. Earth Hour takes place worldwide at 8.30 p.m. local time and is a global call to turn off lights for 60 minutes to raise awareness of the danger of global climatic change (Photo by Fazry Ismail/EPA)

A Pakistani Hindu woman lights candles during Diwali celebrations at a local temple in Lahore, Pakistan, Wednesday, November 11, 2015. Diwali, the festival of lights, is one of Hinduism's most important festivals dedicated to the worship of Lakshmi, the Hindu goddess of wealth. (Photo by K. M. Chaudary/AP Photo)

A small section of the expanding remains of the Veil Nebula, a massive star that exploded about 8,000 years ago. The entire nebula is 110 light-years across, covering six full moons on the sky as seen from Earth, and resides about 2,100 light-years away in the constellation Cygnus, the Swan. Image taken by NASA's Hubble Space Telescope. Released September 24, 2015. (Photo by Reuters/NASA/ESA/Hubble Heritage Team)

Contestants for the Miss World grand final perform in colourful costumes during a dress rehearsal in Sanya, Hainan province, China, 18 December 2015. (Photo by How Hwee Young/EPA)

“DC3 Wreck”. A capture of a US military DC3 plane wreck at the southern black beach in Iceland. Photo location: Iceland. (Photo and caption by Naian Feng/National Geographic Photo Contest)

Children play football in front of an abandoned train compartment next to a railway track in Dhaka, in this May 29, 2014 file photo. (Photo by Andrew Biraj/Reuters)

China's Shang Chunsong prepares to compete in the uneven bars event of the women's individual all-around final artistic gymnastics competition at the Namdong Gymnasium Club during the 17th Asian Games in Incheon, in this September 23, 2014 file photo. (Photo by Kim Hong-Ji/Reuters)

Mikhail Kalashnikov, the father of the world's most popular assault rifle, is handed an AK-74 November 23, 2002 in Izhevsk,1000 East km. from Moscow. November 23 marked the 55th anniversary of the release of the first Kalashnikov gun. According to the Moscow-based Center for Analysis of Strategic and Technologies some 70 million to 100 million Kalashnikovs have been built worldwide since 1947, compared about 7 million to Kalashnikov's Western rival the M-16 assault rifles. (Photo by Oleg Nikishin/Getty Images)