The NASA Extreme Environment Mission Operations (NEEMO) 21 mission began on July 21 as an international crew of aquanauts splashed down to the undersea Aquarius Reef Base, located 62 feet below the surface of the Atlantic Ocean in the Florida Keys National Marine Sanctuary. The NEEMO 21 crew will perform research both inside and outside the habitat during a 16-day simulated space mission. During simulated spacewalks carried out underwater, they will evaluate tools and mission operation techniques that could be used in future space missions, including journeys to Mars. (Photo by Karl Shreeves/NASA)

Lance Cpl. Blas Trevino of the 1st Battalion, 5th Marines, shouts out as he is rescued on a medevac helicopter from the U.S. Army's Task Force Lift “Dust Off”, Charlie Company 1-214 Aviation Regiment after he got shot in the stomach outside Sangin, in the Helmand Province of southern Afghanistan on June 11, 2011. The Army's 'Dust Off' crew needed two attempts to get him out, as they were fired upon and took five rounds of bullets into the tail of their aircraft. (Photo by Anja Niedringhaus/AP Photo/File)

Situated in the Pacific Ocean some 620 miles (1,000 km) from the South American continent, these 19 islands and the surrounding marine reserve have been called a unique “living museum and showcase of evolution”. Photo: “Close-up. We had a juvenile Red-Footed Booby come visit us on the sun deck. I got some closeups with my ultrawide 11-16mm Tokina”. (Photo by Carl Fredrickson)

A member of the United States Naval Academy freshman class wears body armor, helmet and carries a rifle through a mud-filled ditch as part of the “Wet and Sandy” challenge during the rigorous Sea Trials May 17, 2011 in Annapolis, MD. Under strict safety supervision, about 900 freshmen, or “Plebes”, faced 14 hours of 32 rigorous physical and mental challenges during the trials, a daylong, action-oriented event modeled after the Marine Corps 54-hour Crucible and the Navy's Battle Stations. (Photo by Chip Somodevilla/Getty Images)

Singer-songwriter Sheryl Crow meets Clyde the Sea Lion, the star of SeaWorld San Diego's “Sea Lion Tonite”, at the marine-life park's Sea Lion and Otter Stadium on August 3, 2011 in San Diego, California. Crow and her sons spent the day a SeaWorld meeting, feeding and learning about sea turtles, penguins and sea lions, other park animal ambassadors. Crow was performing in San Diego on her summer concert tour with Kid Rock. (Photo by Mike Aguilera/SeaWorld San Diego via Getty Images)

In this handout image provided by the National Oceanic and Atmospheric Administration (NOAA), model runs from the Center for Tsunami Research at the NOAA Pacific Marine Environmental Laboratory show the expected wave heights of the tsunami as it travels across the Pacific basin March 11, 2011. The largest wave heights are expected near the earthquake epicenter, off Japan. The wave will decrease in height as it travels across the deep Pacific but grow taller as it nears coastal areas. In general, as the energy of the wave decreases with distance, the near shore heights will also decrease (e.g., coastal Hawaii will not expect heights of that encountered in coastal Japan). (Photo by NOAA via Getty Images)

Romanian soldiers take part in a joint military exercise with NATO members, called “Agile Spirit 2015” at the Vaziani military base outside Tbilisi, Georgia, July 21, 2015. Georgian soldiers along with U.S. marines and platoon-size units from Bulgaria, Latvia, Lithuania and Romania are taking part in the exercises at the Vaziani military base outside Tbilisi. (Photo by David Mdzinarishvili/Reuters)