Jack Dykinga / South rim of Moran Point at sunrise, with the Colorado River below, Grand Canyon National Park, Arizona, USA

Juan Carlos Munoz / Close up of foot of a hiker on the caldera rim of Los Gemelos, Santa Cruz Island, Galapagos, January 2009. Model released.

Fabio Liverani / Tree frog {Hyla sp} on rim of tropical fungus, Tambopata National Reserve, Amazonia, Peru

Jack Dykinga / Snow on Pinyon Pines (Pinus edulis) at sunrise, East Rim Drive, South Rim, Grand Canyon NP, Arizona, USA

Jack Dykinga / Ponderosa Pine (Pinus ponderosa) pine cone and needles in the snow, South Rim, Grand Canyon NP, Arizona, USA

Jack Dykinga / Sunset at Yaki Point on the South Rim with stratified rim rocks and minute storm clouds inside the canyon below, Grand Canyon National Park, Arizona, USA.

Pete Oxford / Sulphur fulmerole in crater of active volcano, Sierra Negra, Isabela Is, Galapagos

Yva Momatiuk & John Eastcott / Coyote (Canis latrans) looking for handouts from tourists, Mather Point parking lot on South Rim, Grand Canyon National Park, Arizona

Tim Fitzharris / South Rim of Grand Canyon with a dusting of snow seen from Yaki Point, Grand Canyon National Park, Arizona

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large male on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) group wallowing in seasonal pool on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) group wallowing in seasonal pond on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) old male in dry season on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Gavin Hellier / View from the rim into the crater of Ranu Kau, Isla de Pascua / Easter Island, Rapa Nui, Chile, 2008

Gavin Hellier / View from the rim into the crater of Ranu Kau, Isla de Pascua / Easter Island, Chile 2008

Gavin Hellier / View from the rim into the crater of Ranu Kau, Isla de Pascua / Easter Island, Chile 2008

Oriol Alamany / Waves along the beach on South Beach Trail, Pacific Rim National Park. Vancouver Island, British Columbia, Canada

Mark Taylor / Rinjani crater rim at sunset, Lombok, Indonesia.

Mark Taylor / Rinjani crater rim at sunset, Lombok, Indonesia.

Tui De Roy / Pink iguana (Conolophus marthae) Northern caldera rim, Wolf Volcano, Isabela Island, Galapagos Islands, Ecuador, Critically endangered species

Tui De Roy / Pink iguana (Conolophus marthae) in dry habitat on caldera rim, Wolf Volcano, Isabela Island, Galapagos Islands,Critically endangered species

Tui De Roy / Volcan Alcedo giant tortoises (Chelonoidis nigra vandenburghi) among steaming fumaroles on western caldera rim, Alcedo Volcano, Isabela Island, Galapagos Islands, Ecuador

Nick Garbutt / Malay or Oriental Civet (Viverra tangalunga) foraging at night on heath forest floor on the southern plateau rim of Maliau Basin, Sabah's 'Lost World', Borneo

Kevin Schafer / Aerial view of crater rim on south slope of Mount St Helens, Mount St Helens National Volcanic Monument, Washington

Donald M. Jones / California Condor (Gymnogyps californianus), tagged with radio transmitter, South Rim of Grand Canyon, Arizona

Pete Oxford / Galapagos Giant tortoise (Geochelone elephantophus vandenburghi) grazing on rim of crater, Alcedo Volcano, Isabela Island Galapagos islands, Ecuador, South America

Pete Oxford / Galapagos Giant tortoise (Geochelone elephantophus vandenburghi) on rim of crater, with fumaroles behind (emitting steam and gas) Alcedo Volcano, Isabela Island, Galapagos islands, Ecuador, South Amer...

Pete Oxford / Galapagos Giant tortoise (Geochelone elephantophus vandenburghi) on rim of Alcedo Volcano, Isabela Island, Galapagos islands, Ecuador, South America

Tui De Roy / Galapagos Land Iguana (Conolophus subcristatus) on caldera rim, Galapagos Islands, Ecuador

Steven Kazlowski / Common raven (Corvus corax) on south rim of Grand Canyon National Park in winter, Arizona, USA. February.

Steven Kazlowski / Common raven (Corvus corax) on south rim of Grand Canyon National Park in winter, Arizona, USA.

Steven Kazlowski / South rim of the Grand Canyon National Park in winter, Arizona, USA. February 2009.

Steven Kazlowski / South rim of the Grand Canyon National Park in winter, Arizona, USA. February 2009.

Steven Kazlowski / Mule deer (Odocoileus hemionus) large bull on the south rim of the Grand Canyon in snow. Grand Canyon National Park, Arizona, USA.

Juan Carlos Munoz / Hikers admire the view from the caldera rim of the Chico Volcano, Sierra Negra, Isabela Island, Galapagos, January 2009

Juan Carlos Munoz / Hikers admire the view from the caldera rim of the Chico Volcano, Sierra Negra, Isabela Island, Galapagos, January 2009

Juan Carlos Munoz / Tourists riding horses to the caldera rim of the Chico Volcano, Sierra Negra, Isabela Island, Galapagos, January 2009

Juan Carlos Munoz / View from the caldera rim of Los Gemelos, Santa Cruz Island, Galapagos, January 2009

Pete Oxford / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) on rim of volcano, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Pete Oxford / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) on rim of volcano, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Pete Oxford / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) on rim of volcano, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Pete Oxford / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) on rim of volcano, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Pete Oxford / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) on rim of volcano, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Pete Oxford / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) on rim of Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Fabio Liverani / Tiny Tree frog {Hyla sp} on rim of tropical fungus, Tambopata National Reserve, Amazonia, Peru

Thomas Marent / Red Rim (Biblis hyperia) butterfly, Colombia

Tim Fitzharris / Clearing skies over the South Rim, Grand Canyon National Park, Arizona

Jack Dykinga / South Rim rock formation known as "Duck on a Rock" at sunset, with the "Vishnu Temple" in the background, Grand Canyon NP, Arizona, USA

Jack Dykinga / Orange Lichen and Agave (Agave utahensis) on trailside rim rock, South Bass Trail, Grand Canyon NP, Arizona, USA

Jack Dykinga / Moran Point, South Rim, Grand Canyon National Park, Arizona, USA with scattering of first winter snow.

Tim Fitzharris / Wotan's Throne from South Rim, Grand Canyon National Park, Arizona

Tui De Roy / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) dew laden spider webs around fumarole vents, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) large males vie for space in coveted rainy season wallows, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

JIM CLARE / Aerial view of Cotopaxi volcano crater in snow, Ecuador

HUW CORDEY / View of South Rim, Grand Canyon National Park, Arizona, USA

Pete Oxford / View from rim of cone of active volcano, Sierra Negra, Isabela Is, Galapagos

Pete Oxford / Rocks on rim of cone of active volcano, Sierra Negra, Isabela Is, Galapagos.

Nigel Bean / View across Grand Canyon from South Rim, Arizona, USA.

Pete Oxford / Sulphur crystals from crater of active volcano, Sierra Negra, Isabela Is, Galapagos

Gavin Hellier / Panoramic view of the Grand Canyon from South rim at dusk, Arizona, USA

Gavin Hellier / Panoramic view of South Rim with clearing winter storm, Grand Canyon NP, Arizona, USA

Yva Momatiuk & John Eastcott / Coyote (Canis latrans) illegally fed by tourist in spite of warning signs, Mather Point Parking, South Rim, Grand Canyon National Park, Arizona

Yva Momatiuk & John Eastcott / Tourist depositing plastic bottle into recycling garbage cans in parking lot, South Rim, Grand Canyon National Park, Arizona

Yva Momatiuk & John Eastcott / Recycling garbage cans in parking lot, South Rim, Grand Canyon National Park, Arizona

Tim Fitzharris / View of the South Rim from Pima Point, Grand Canyon National Park, Arizona

Tim Fitzharris / South Rim of Grand Canyon with a dusting of snow, Grand Canyon National Park, Arizona

Tui De Roy / Galapagos Hawk (Buteo galapagoensis) overlooking sulphur fumaroles on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) searching for water amid steaming fumaroles on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) wallowing in pool at sunrise, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) amid steaming fumaroles along caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) group searching for moisture among steaming fumaroles on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) group searching for moisture among steaming fumaroles on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large male on caldera rim, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) wallowing in temporary rainy season pool, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large males on caldera rim, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large male wallowing in temporary rainy season pool, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large males vie for space in coveted rainy season wallows, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large males vie for space in coveted rainy season wallows, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large males vie for space in coveted rainy season wallows, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large males vie for space in coveted rainy season wallows, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Hawk (Buteo galapagoensis) overlooking sulphur fumaroles on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) on caldera rim at sunrise, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Land Iguana (Conolophus subcristatus) female on caldera rim, Fernandina Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Land Iguana (Conolophus subcristatus) carcass and scorched vegetation from volcanic eruption, Caldera Rim, Fernandina Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Land Iguana (Conolophus subcristatus) and vegetation scorched by fresh scoria fall on caldera rim, Fernandina Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large male at sunrise, caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) large male on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Hawk (Buteo galapagoensis) pair landing on snags near sulphur fumaroles on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) group wallowing in seasonal pond on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) searching for moisture among steaming fumaroles on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) amid steaming fumaroles on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) wallowing in seasonal pool on caldera rim, Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Galapagos Giant Tortoise (Chelonoidis nigra) seeking moisture in fumarole steam on caldera rim of Alcedo Volcano, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Chinstrap Penguin (Pygoscelis antarctica) colony of 75,000 pairs nesting along volcanic crater rim, Deception Island, South Shetland Islands, Antarctica