In this March 22, 1975 file photo, a refugee clutches a baby as a government helicopter gunship carries them away near Tuy Hoa, Vietnam, 235 miles northeast of Saigon. They were among thousands fleeing from Communist advances. AP Photographer Nick Ut will be retiring from the AP in March 2017 after 51 years of taking photographs from the front lines of the Vietnam War to the red carpets of Hollywood. (Photo by Nick Ut/AP Photo)

Vietnam’s Son Doong cave, the largest in the world, could hold a 40-story skyscraper inside. The pristine ecosystem has its own river and jungle. Despite its size, Son Doong wasn’t discovered until 1991. It was lost again for nearly two decades and was fully explored for the first time in 2009. (Photo by Jason Speth/HuffPost)

Models pose in designs from May Quant's collection on a street in London, England, on October 16, 1969. Grania, left, wears the "Shimmy Shimmy," a white rayon dress over matching pants with a shawl. Baba, center, wears "Razzamatazz," a jumpsuit featuring plastic sequins in blue, silver and red on nylon. Linda wears "Muffit," a pink minidress with an old English style floppy mobcap. (Photo by AP Photo)

“These Rajasthani sisters were sitting on the staircase inside their house relaxing and enjoy a cup of masala chai”. (Photo by Firdaus Hadzri/National Geographic Travel Photographer of the Year Contest)

A Rohingya refugee girl named Rufia Begum, aged 9, poses for a photograph as she wears thanaka paste at Balukhali camp in Cox's Bazaar, Bangladesh, March 31, 2018. (Photo by Clodagh Kilcoyne/Reuters)

An anti-coup protester holds a Burkinabe flag in Ouagadougou, Burkina Faso, September 18, 2015. Security forces in the capital of Burkina Faso fired in the air on Friday to disperse demonstrators who burned tyres and blocked neighborhood streets to protest at a military coup this week that derailed a democratic transition. The head of a military junta in Burkina Faso which took power on Thursday has freed interim President Michel Kafando and two of his ministers, state television said on Friday. (Photo by Joe Penney/Reuters)

This stirring collection of photos which offer a glimpse behind the scenes of army life have all been selected as winners in an annual competition. The remarkable pictures in the Army Photographic Competition show Britain's soldiers at work and play. They have been taken by amateur and professional soldier cameramen and include images from operations in Afghanistan, air shows and sporting events. The winners were announced at a ceremony held at the Army Headquarters in Andover in Hampshire. (Photo by Jamie Peters/MoD/Geoff Robinson Photography/REX Features)

Imagine living in the sea where it is permanently dark, cold, and food is hard to find. For many animals at depth, it may be weeks to months between meals. If you find something to eat, you have to hang on to it. This is why so many deep-sea fishes have lots of big teeth. This dragonfish, spotted off the coast of Australia, even has teeth on its tongue. They would be terrifying animals ... if they weren’t the size of a banana. (Photo by Julian Finn/Museum Victoria)