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Diving Into the Great Barrier Reef

To say that the Great Barrier Reef is the world's largest coral reef may be understating things; the Australian government notes that it is "the only living organic collective visible from Earth's orbit." Certainly, it is vast—a conglomeration of some 3,000 reefs and 600 islands stretching more than 1,250 miles along Australia's northeast coast. Green turtles, dolphins and whales live there, along with 200 species of birds, 1,500 species of fish, 4,000 species of mollusks and, yes, an abundance of corals.

But big does not mean indestructible. The Great Barrier Reef Marine Park Authority, which has jurisdiction over much of the reef, has taken steps to control water pollution, conserve coastal wetlands and set rules for who can do what and where. Global warming is a more difficult challenge: rising sea temperatures are causing mass coral bleaching—episodes in which corals lose their color after expelling the one-celled algae that live within their tissues. This is a sign of stress, and it can kill afflicted corals. A recent report by the Intergovernmental Panel on Climate Change projects annual bleachings by as early as 2030. One possible result: a "functionally extinct" ecosystem by 2050.

The reef attracts about two million visitors a year, but that's OK, says Terry Hughes, director of the Australian Research Council's Centre of Excellence for Coral Reef Studies. "The tourism industry is an active advocate for the reef," he explains. "Tourists are taught to look but not touch, and to be careful when reef walking or snorkeling."

The Pyramids of Giza

The Pyramids of Giza rise from the west bank of the Nile River almost as an act of defiance, perfectly symmetrical behemoths imposed upon a flat, barren landscape. The Great Pyramid—the oldest, largest and most famous of the monuments—is the last of the ancient world's "seven wonders" still standing. Built 4,500 years ago as a tomb for the fourth dynasty pharaoh Khufu, it once stood 481 feet high. Because thieves (who robbed the burial chambers) stripped the pyramids of their outer casings of polished white limestone, they no longer reach their original heights. Today the Great Pyramid stands at 450 feet.

Precisely how the Egyptians built these colossal structures is still a matter of debate. To construct the Great Pyramid, workers had to cut, haul and assemble 2.3 million limestone blocks, weighing on average more than two tons. Contrary to the long-held belief that the workers were slaves, Egyptologists now believe the pyramids were ancient public works projects (which, unlike modern public works projects, actually got finished).

Erected as a vanity effort by a ruthless pharaoh, the pyramids remain first and foremost a monument to the ingenuity of a remarkable civilization. As Jean-Pierre Houdin, a French architect who has studied the Great Pyramid for almost a decade, observes, "You don't build such a mountain of stones with so few people this size unless you have reached a very high level of knowledge in many sciences."