Where Did All the Giant Mammals Go?

Mystery of the Pyramids Solved

One of the great mysteries of the pyramids may have been solved—by state-of-the-art radar systems that can penetrate the desert sand. The Egyptian pharaohs built 90 pyramids, with the most famous, at Giza, constructed almost 5,000 years ago. At nearly 500 feet, the Great Pyramid of Khufu was the world’s tallest manmade structure for almost 4,000 years! To build it, 20,000 workers assembled 2.3 million stone blocks, each weighing tons. Scientists have long wondered how ancient people, without modern energy, wheels, pulleys or even iron tools, could have cut and moved such massive stones from the quarries in eastern Egypt to the pyramid sites. It was long thought they were transported by boat along the Nile—but many pyramids are miles from the river. From today’s river that is. Recently, satellite and ground penetrating radar identified an ancient tributary of the Nile that ran next to many of the pyramid complexes. The advanced radar even revealed what may have been ports, to deliver the stone blocks and huge labor force. These channels filled with desert sand when the region dried out millennia ago, and centuries of agriculture obscured the geologic signs of the tributary. This finding also suggests there may be entire settlements along the ancient waterway that were entombed by the desert—just waiting to be discovered.

Where Did All the Giant Mammals Go?

After the dinosaurs, giant mammals ruled Earth for millions of years—then suddenly, most of them disappeared. What happened? When the Chicxulub asteroid struck, and plunged Earth into darkness and cold, large dinosaurs became extinct. Early mammals—small, warm-blooded and covered in fur—were able to survive. And, over a few million years, they grew in size to occupy the environmental niches the dinosaurs had vacated. There were bears the size of rhinos, and rhinos the size of elephants. There were 400-pound beavers and 10-foot-tall ground sloths. They existed from 50 million years ago until around 50,000 years ago. Then, rather suddenly, most went extinct. There are two hypotheses. As Earth’s climate warmed, some areas became too wet and boggy to support large animals. Other areas dried out and lost their vegetation. Without plants to eat, herbivores starved. Without herbivores to eat, carnivores starved. Who didn’t starve? Us. Humans. The other related hypothesis is that humans, as we migrated around the globe, found large mammals to be an excellent food source. Hunting pressure on these slow-reproducing animals, especially in Australia and North America, may have caused their populations to crash. In Africa, though, where humans originated, we’d reached more of an equilibrium with megafauna, and 80% of large mammals still survive.

Frogsicles

Many animals hibernate, but only the wood frog can freeze solid in winter—its heart and brain stopping completely—then thaw and come back to life in the spring. Its process to do this is fascinating … and could one day save human lives. The danger with freezing is ice. If water freezes within a cell, sharp ice crystals will puncture or rupture cell walls and kill the cell, which normally kills the animal. So, as temperatures drop, the wood frog’s liver converts glycogen to glucose, a sugar syrup, and floods the frog’s system. Meanwhile, nucleating proteins push water from the frog’s cells. Glucose replaces the water, which keeps the cells from freezing. Outside the cells, the water does freeze, which stops the frog’s metabolism, including its brain and heart, and preserves its tissues. In spring, the frog thaws, its brain and organs come back to life, and breeding season begins. Several other animals use chemical antifreezes to avoid ice crystals forming within their cells. And now researchers are trying to do the same with human organs harvested for transplant. Organs currently remain viable for only a few hours outside the body. But if glucose could replace the water within them, perhaps they too could be frozen solid and later reanimated, greatly prolonging transplant time. A potentially life-saving technique for humans, learned from the humble wood frog.

Drilling into Earth’s Mantle

Turns out it was much easier to go to outer space than to inner Earth. In the 1950s, the U.S. and Russia began competitive spaceflight programs. Twenty-five years later, the U.S. Voyager spacecraft had gone 10 billion miles into space. Around the same time, both countries also began drilling programs trying to pierce through Earth’s crust to reach the mantle below. The U.S. project began drilling off the coast of Mexico, because scientists had recognized that oceanic crust is thin, averaging only 4 miles thick, whereas continental crust could be 25 miles thick. But the project was defunded by Congress after only a test bore. The Russians began drilling on land, above the Arctic Circle, and kept at it for 20 years. In the end, they got 8 miles into the crust without ever reaching mantle. But last year, an international expedition on the Resolution, the drilling ship we discussed on a prior episode, set out for the Atlantis Massif. Discovered in the seventies, it’s a huge bulge that rises 14,000 feet above the mid-ocean seafloor. Here, the ocean crust is even thinner, separating into layers as it spreads apart, exposing deep rock that is normally far below Earth’s surface. By drilling less than a mile into this spreading area, the Resolution finally tapped into mantle and brought core samples to the surface—a geologic first, 66 years in the making!

How Planets Get Moons

The Moon has inspired humans for countless generations. Among moons, ours is large, about a quarter the size of Earth. But we have only one. Other planets have many. And some have none. Where do they come from, and how do planets acquire them? Our moon is unique in the solar system. It came from an impact, when an asteroid the size of Mars slammed into Earth 4 billion years ago and smashed off a body that would become the Moon. Other moons are ancient astral bodies that were created along with the planets when the solar system took shape. Still more are former asteroids, which passed near enough to a planet to be captured in its orbit. Small planets closer to the Sun have small gravitational fields. In order to trap a passing asteroid, these would have to combat a stronger gravitational pull from the nearby Sun. For this reason, Mercury and Venus have no moons. Large planets farther from the Sun have stronger gravitational fields that can more easily overcome a weaker pull from the distant Sun, so they have many moons—95 for Jupiter and 146 for Saturn—more than any other planet. Some of those moons are nearly the size of Earth, may have oceans, and may even have undersea life, as we’ve talked about in prior episodes. These moons may be targets for future space missions, inspiring humans of future generations.