This is the amazing moment a heroic hippo saved a gnu from certain death. After being bitten by a crocodile, the large antelope is seen being dragged slowly under the water. But in a miraculous turn of events, a nearby hippo is seen making its way across the water to help the animal in its hour of need. Photo: One of the biggest hippos protects the gnu as it makes its way back to the shoreline, guarding it from any further attacks. (Photo by Vadim Onishchenko/Caters News)

“This is the terrifying moment a diver came head to head with a shark as it swims inches away snatching a bite for dinner. The close encounter, captured off Bimini Island in the Bahamas, shows the hammerhead approaching diver Eli Martinez who bravely stands his ground as the giant beast approaches. Eli, free diving outside of a protective cage, carefully handled the sea creature despite its menacing razor-sharp teeth – but admitted they are extremely shy and need a lot of work to allow divers close to them. After multiple trips and hours of diving nearby they finally got used to Eli in January this year – hammerheads regularly visit these waters during the winter season”. – Caters News. Photo: Eli Martinez with hammerhead shark. (Photo by J. P. Zegarra/Caters News)

Beautiful, strange and occasionally alarming pictures from the shortlist for this year’s Wellcome image awards – which celebrate the very best in science photography and imaging – from an x-ray of a bat to a micrograph of a kidney stone. The exhibition opens on 12 March at three science centres and the Museum of Science and Industry in Manchester. Photo: Scanning electron micrograph (SEM) of an Arabidopsis thaliana flower, also commonly known as thale cress. Some of the anthers are open, revealing pollen grains ready for dispersal. Arabidopsis was the first plant to have its entire genome sequenced and is widely used as a model organism in molecular and plant biology. Horizontal width of image is 1200 microns. Magnification 100x. (Photo by Stefan Eberhard/Wellcome Images)

A partially frozen Niagara Falls is seen on the American side lit by lights during sub freezing temperatures in Niagara Falls, Ontario March 3, 2014. (Photo by Mark Blinch/Reuters)

“These are the astonishing images of the very aptly named door to hell, a fiery crater thats baffled scientist and has been flaming away for more than 40 years. The crater is 230-feet wide and situated near Derweze village in Turkmenistan”. – Caters News. (Photo by William Keeping/Caters News)

Two male African mantis Pseudempusa pinnapavonis (Peacock Mantis) show their colours in Igor's home studio in Munich, Germany. (Photo by Igor Siwanowicz/Barcroft Media)

A large storm cloud covers the Sydney CBD on March 5, 2014 in Sydney, Australia. A severe thunderstorm warning was issued for the Sydney metropolitan area late this afternoon with heavy rainfall due to cause flash flooding in areas. (Photo by Cassie Trotter/Getty Images)