Sir David Attenborough at the Beijing Museum of Natural History with fossil of Juramaia, as featured in the Smithsonian Channel series Rise of Animals: Triumph of the Vertebrates. Courtesy Smithsonian Channel hide caption

itoggle caption Courtesy Smithsonian Channel

Hudson River view. Brian Mann/North Country Public Radio hide caption

itoggle caption Brian Mann/North Country Public Radio

A view of Seattle from the Bullitt Center. Brad Kahn/Flickr hide caption

itoggle caption Brad Kahn/Flickr

All of our scientific tools have limits. These limits ensure that we will never see the whole picture. We can never have complete knowledge of the universe. Above, the ESO's APEX radio telescope probes the heavens from its lonely perch on Chile's Chajnantor plateau. Gordon Gillet/ESO hide caption

itoggle caption Gordon Gillet/ESO

Will the distant future give rise to exhibits of a human past long gone, much as we gawk today at representations of a dinosaur age we can only imagine? Aamir Qureshi/AFP/Getty Images hide caption

itoggle caption Aamir Qureshi/AFP/Getty Images

The Sundarbans, a mangrove forest at the edge of the Bay of Bengal, stretch across parts of southwestern Bangladesh and southeastern India. NASA hide caption

itoggle caption NASA

Coprates Chasma in the Valles Marineris on Mars, photographed by the Mars Express spacecraft. Appearing in the top half of this image, it ranges from 60-100 km wide and drops 8-9 km below the surrounding plains. G. Neukum/ESA/DLR/FU Berlin hide caption

itoggle caption G. Neukum/ESA/DLR/FU Berlin