A coral reef is built by multiple coral animals, which live together in colonies. These colonies are formed by one original coral polyp -- a mouth surrounded by tentacles -- that divides itself in half over and over and over. All of these new twins stay connected to one another and build a skeleton underneath themselves, so that they can grow up toward the sunlight. The result is similar to a group of hundreds of tiny anemones living shoulder-to-shoulder on the surface of a rock. The star coral here is preparing to spawn, holding a bundle of gametes in each of its mouths (about 100 of them in this shot). The bright green color at the ends of the tentacles is produced by the coral’s own sunscreen-like pigments while the brown color is produced by the algae living inside the coral’s tissue. The light pink color is the gamete bundles, each made up of 50-100 eggs glued together with sperm. Yes, that’s right… they’re hermaphrodites. Not every coral is, but in this particular species each individual animal makes both eggs and sperm. But one individual coral colony can’t fertilize itself, so it still has to find a partner to mate with. How do you find a mate when you’re stuck to the bottom of the ocean? Most spawning coral species solve this puzzle by sending their sperm and eggs to meet at the water surface, cleverly turning a three-dimensional problem into a two-dimensional one. Photo: Kristen Marhaver.

Each year in September, corals in the Caribbean stage a mass spawning event. Witnessing it, says marine biologist and TED Fellow Kristen Marhaver, is like swimming inside a snow globe. Here, she explains how corals beget corals — and how she and her fellow scientists are trying to help them along.

Cascadia Expeditions' Brett Gallagher and civil engineer Tyler Deboodt photographed in the entrance to Snow Dragon minutes before sunset in July 2013. Says McGregor, he wouldn't be surprised if the cave was destroyed by 2016. Once skylights form, air flows through the cave at an accelerated rate, which weakens the caves' structure and causes them to collapse.

Explorer Brent McGregor shares stunning photographs of glacier caves discovered within the Sandy Glacier on Oregon’s Mount Hood.

For girls in rural Yemen, just getting permission to go to school can be an obstacle. Here, first-graders sit five to a bench. Classrooms often number 150 students to one teacher.

Photographer Laura Boushnak celebrates success stories in women’s education across the Arab World.

For “New Books of Knowledge” (2009) Dettmer reveals geographic images to show this encyclopedia as a landscape.

Image courtesy of the artist and Packer Schopf.

To create new art, sculptor Brian Dettmer cuts up old books. See a gallery of his intricate, breathtaking creations.

There is no "after Ferguson" | Photo: Jon Lowenstein

In advance of the grand jury verdict, photojournalist Jon Lowenstein talks about what he saw in Ferguson, Missouri. With photos and video.

Photo by Iwan Baan

On three tiny islands in central Japan, stunning natural beauty lives side by side with some of the world’s best contemporary art and architecture. See 10 photos by Iwan Baan.

TED’s presented our share of near-misses and might-never-happen tech demos — including, depending on how you count, at least 5 flying cars.