Photographs by: Antarctica: Adeliepenguin, Dreamstime; Yosemite: Lorcel G, Dreamstime; Great Barrier Reef: Pniesen, Dreamstime; pyramids: Sculpies, Dreamstime; Shanghai street: Pixattitude, Dreamstime; national mall: Mazuciukas, Dreamstime; sledding: Sonya Etchison, Dreamstime; climbing tree: Ziggymars, Dreamstime; swimming: Alexander Shalamov, Dreamstime; reading: Petro, Dreamstime; kid with camera: Tatyana Gladskikh, Dreamstime; stargazing: Pere Sanz, Dreamstime; dogsled: Alexander Piragis, Dreamstime; climbing rocks: Petr Cihak, Dreamstime; kayak: Alexander Shalamov, Dreamstime; airplane: Wisconsinart, Dreamstime; walking down sidewalk: Susan Leggett, Dreamstime; family in car: Arne9001, Dreamstime; winter jacket: Nikolai Sorokin, Dreamstime; climbing gear: Swinnerrr, Dreamstime; wetsuit: Nadezda Ledyaeva, Dreamstime; hat: Juan Moyano, Dreamstime; vest: Anton Starikov, Dreamstime; blazer: Chiyacat, Dreamstime; Arctic tern: Jarcosa, Dreamstime; ibex: Jayone1981, Dreamstime; sea turtle: Lunamarina, Dreamstime; mouse: Icefront, Dreamstime; bee: T3rmiit, Dreamstime; barn owl: Miroslav Hlavko, Dreamstime; Sylvia Earle: Bates Littlehales, National Geographic Creative; Mattias Klum (photographer): Mattias Klum, National Geographic Creative; Borge Ousland: Borge Ousland, National Geographic Creative; Mike Libecki (climber): John Burcham, National Geographic Creative; Thomas Levy (archaeologist): Kenneth Garrett, National Geographic Creative; Kevin Hand (astrobiologist): Mark Thiessen, National Geographic Creative