Gers, traditional Mongolian tents, are seen on a hill in an area known as a ger district in Ulan Bator June 26, 2013. Approximately 60 percent of the population of Ulan Bator live in settlements known as ger districts and in many cases residents have limited access to basic services such as water and sanitation. According to a 2010 National Population Center census, every year between thirty and forty thousand people migrate from the countryside to the capital Ulan Bator. Ger districts in the city have been expanding rapidly in recent years. Mongolia is the world's least densely populated country, with 2.8 million people spread across an area around three times the size of France. (Photo by Carlos Barria/Reuters)

NASA says it could be another 20 years before humans touch down on Mars, but in a sense, the Mars Society has been exploring the red planet for more than a decade – in Utah. Photo: Csilla Orgel, a geologist of Crew 125 EuroMoonMars B mission, makes her way back to the Mars Desert Research Station (MDRS) in the Utah desert March 3, 2013. The MDRS aims to investigate the feasibility of a human exploration of Mars and uses the Utah desert's Mars-like terrain to simulate working conditions on the red planet. Scientists, students and enthusiasts work together developing field tactics and studying the terrain. All outdoor exploration is done wearing simulated spacesuits and carrying air supply packs and crews live together in a small communication base with limited amounts of electricity, food, oxygen and water. Everything needed to survive must be produced, fixed and replaced on site. (Photo by Jim Urquhart/Reuters)

When Dutch photographer Marcel Heijnen moved to Hong Kong, the territory’s shop cats instantly caught his eye. While the “feline emperors” are the stars, his shots also offer insights into Hong Kong’s wares, from dried fish to paper. Here: Hong Kong Shop Cats #17. (Photo by Marcel Heijnen/Blue Lotus)

Lisandra Perez, 7, practices in his house before his flute lesson at the Integral System of Artistic Education for Social Inclusion (SIFAIS) center in the poor neighborhood of La Carpio, Costa Rica October 8, 2015. SIFAIS center is developing a social program with the help of 156 volunteers who teach art, music, sports and education, for children and youth living in La Carpio, known for being the home to gangs, violence, drugs and social vulnerability, according to the centre. (Photo by Juan Carlos Ulate/Reuters)

An internally displaced woman collects water from a pond to construct a mud-house at the Aboushok camp in El Fasher, North Darfur, Sudan, November 17, 2015. The conflict in Sudan's Darfur region that erupted 12 years ago shows no sign of ending. But it hasn't stopped displaced youngsters, some of whom have spent their entire lives in refugee camps, from dreaming big. Twelve children aged 12 explain their hopes and dreams for the future; ambitions include becoming a doctor, an engineer and a teacher. (Photo by Mohamed Nureldin Abdallah/Reuters)

Biologists Jenna Cormany (L) and Lauryn Wright of the South Carolina Department of Natural Resources help to release a leatherback turtle in Isle of Palms, South Carolina March 12, 2015. The 475-pound turtle was the first living leatherback turtle to be recovered in South Carolina and one of only a handful ever treated at rehabilitation facilities in the United States. It was found March 7 on the beach on Yawkey-South Island Reserve, a 3.5-mile-long (5.6-km-long) barrier island and wildlife preserve near Georgetown, South Carolina. (Photo by Randall Hill/Reuters)

“The giant clam, Tridacna gigas (known as pā’ua in Cook Islands Māori), is the largest living bivalve mollusc. T. gigas is one of the most endangered clam species. It was mentioned as early as 1825 in scientific reports. One of a number of large clam species native to the shallow coral reefs of the South Pacific and Indian oceans, they can weigh more than 200 kilograms (440 lb) measure as much as 120 cm (47 in) across, and have an average lifespan in the wild of 100 years or more”. – Wikipedia

Photo: Tridacna Gigas, or Giant Clams spew water as a traditional fisherman passes by a small sanctuary on January 23, 2004 near Bolinao in the Northern Philippines. The clams, prime builders for coral reefs and providing shelter for spawning fish and other marine life, are exposed by low tides in the sanctuary. Overfishing and pollution throughout the country are not only threatening food security, but are also starting to choke one of the few working clam sanctuaries in the world. (Photo by David Greedy/Getty Images)