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These are the facts you could find on this page:
Adjustable Tires, Alien Sand Dunes, Atomic Clocks, Black And White Moon, Body Glue, Breathable Liquid, Brown Dwarfs, Coin Notches, Complex Crystals, Coral Atolls, Deepest Cave, Early Ocean Explorers, Electron Microscopes, Evaporated Sea, Expanding Lizard, Giant Antlers, Giant Construction Project, Glass Shells, Halogen Light Bulbs, Heavy Ice, Hops in Beer, Human Genome Size, Humming Fish, Insect Sweat, Largest Eyes, Largest Star, Light Catching Chemical, Light Catching Molecule, Microgravity Robot, Milky Way's Shape, Momentum Exchange Tether, Most Islands in a Lake, Muddiest River, Nest Impostor, New Kinds of Planets, Nimble Insects, Ocean Creatures, Ocean Walking Insect, Oldest Stars, Penguin Boat, Prehistoric Creatures, Protein, Robot Community, Rock Varnish, Rotary Rocket, Round Portholes, Scale Eaters, Shrinking Compound, Sinking Ground, Slow Heart, Smart Birds, Spherical Fish, Sunken Continent, Sun's Core, Swimming Ants, Thickest Skin, Tree Kangaroos, Twig Camouflage, Ultra-Thin Layers, Whale Ancestors

Adjustable Tires
The High Mobility Multi-Purpose Wheeled Vehicle (HMMWV) or Hummer is a highly durable motor vehicle that was originally designed for military use. A Hummer has the ability to change tire pressure while it is moving, making it practical for travel across loose surfaces like sand dunes.
The Hummer was designed to be dropped by parachute and land on its wheels unharmed. Its other interesting talents include a winch powerful enough to suspend the vehicle in midair, and, in the military version, the ability to ford streams as deep as 60 inches (150 centimeters).
The civilian version of the Hummer, which became available in 1992, is not available with a machine gun or rocket launcher, but it is just as durable as the military version.
(Hummer is a trademark of AM General.)

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Alien Sand Dunes
Scientists have recently discovered active sand dunes on Mars. The Viking spacecraft, which photographed the planet in the 1970s, hinted at the presence of sand dunes. Cameras aboard the Mars Global Surveyor spacecraft, which is currently mapping the planet in great detail, returned more precise images of the dunes and showed that they are active (moving).
There are two kinds of dunes: small fields of bright dunes, which may be made of gypsum or another sulfate mineral, and large areas of darker dunes, which might be made of eroded particles of volcanic rock.
The Martian sand dunes form where winds bring in other particles to replace the reddish-brown dust that accumulates in most places on Mars. Scientists believe the winds on Mars are only strong enough to move the sand during part of the year, because the air is too thin at other times.

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Atomic Clocks
The most accurate clocks in the world are atomic clocks, which use the vibrations of atoms to keep track of the time. They are so accurate that they would gain or lose only one second in three million years.
Most clocks use mechanical or electronic oscillators (vibrators) to count out a fixed number of "ticks" per second. The oscillators are not all exactly the same, so ordinary clocks must be periodically reset.
Atomic clocks use the absolutely stable vibrations of atoms (usually cesium atoms). Since every atom of the same type vibrates exactly the same number of times each second, atomic clocks are extremely accurate.
The largest error in the best atomic clocks comes from slight variations in how the atoms are moving as their vibrations are measured. New atomic clocks will slow the atoms down almost to a stop, making them up to 10,000 times more accurate than today's models.

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Black And White Moon
The most contrasting object in our solar system is Saturn's moon Iapetus (eye-AP-i-tus). The albedo (reflectance) of its leading hemisphere (the half that stays in front as it orbits Saturn) is less than 0.05, about as dark as soot. The trailing hemisphere has an albedo of 0.5, as bright as water ice.
The difference in brightness is so great that Iapetus' discoverer, Giovanni Cassini, noticed he could only see the moon during half of its orbit.
Astronomers wonder if the dark material may be debris from one of Saturn's darker moons, Phoebe. From its density, astronomers believe Iapetus must be made almost entirely of water ice, which makes the dark hemisphere especially puzzling.

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Body Glue
The most abundant protein in animal tissues is collagen [KOL-uh-gen], a kind of "glue" that holds the body together. The 14 different kinds of collagen account for about 30% of all the protein in our bodies.
Collagen shapes the structures of tendons, bones, cartilage and connective tissue. It also strengthens the skin, and attaches it to the underlying muscles. It makes up most of the "gristle" part of cooked meat.
Why is collagen such great cellular glue? Its molecules are shaped like long, thin rods, with many attachment points where they can be stuck together. They can form strong, rigid structures, and they can be firmly attached to many other kinds of molecules.

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Breathable Liquid
Doctors are using a liquid called perflubron to save the lives of people who might otherwise die of lung congestion. The non-water- based fluid fills the lungs, displacing the watery fluids that otherwise would accumulate there and possibly drown the patient.
Perflubron is a perfluorocarbon, a liquid that is closely related to the plastic teflon. It does not mix with water, and it evaporates in air. Because it carries oxygen and carbon dioxide almost as well as plain air does, it can be used instead of air in the lungs. The technique is called "liquid ventilation."
Tests are under way now to determine the best way to perform liquid ventilation. It is hoped that it can be used to save the lives of premature infants, who often experience lung failure because of fluid accumulation.

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Brown Dwarfs
Objects that are smaller than a star but many times the size of Jupiter are called brown dwarfs. Bearing some similarities to both planets and stars, they do not qualify as either. Some brown dwarfs float freely in space, and others, like planets, orbit stars. Although they are similar to the small, dim stars called red dwarfs, brown dwarfs do not have enough mass to start the process of hydrogen fusion in their cores, and therefore cannot generate the same level of energy as a star.
Over billions of years a brown dwarf will slowly cool, releasing the heat generated by the gravitational collapse which occurred when it first formed from gas and dust. As it cools, it fades; the older a brown dwarf is, the dimmer it is.
Until recently, brown dwarfs were purely theoretical objects; their dark color and faint intensity made them difficult to see. New techniques in astronomy have allowed several to be discovered, some even quite close to our Solar System.

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Coin Notches
United States dimes, quarters, and half dollars have notches all around their edges, but pennies and nickels have no notches.
Notches are a remnant from days when the value of a coin was determined by the amount of silver or gold it contained. The US mint incorporated the notches as a way of discouraging people from shaving off small amounts of the precious metals from their coins. Less valuable coins have always contained only cheaper metals, and so their smooth edges were allowed to remain.
Although coins today no longer contain silver, the notches have been kept as part of their design, and are useful for recognition by the visually impaired.

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Complex Crystals
Mineralogists at the Canadian Museum of Nature and the University of Copenhagen were surprised when they began analyzing specimens of eudialyte, a mineral that is an important source of the rare, expensive metal zirconium.
After finding inconsistencies in x-ray diffraction patterns, which are often used to study the crystal structures of minerals, they conducted further studies that revealed as many as 46 different chemical elements could be part of eudialyte's crystal structure.
Eudialyte's unusually complex structure includes many places where rare elements might be incorporated. Understanding that structure might make the refining of zirconium and other rare elements more practical. As a result of this study, several new varieties of eudialyte have been discovered.

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Coral Atolls
A coral atoll is a ring-shaped island or arc of islands, made almost entirely out of coral, with a shallow, sandy central lagoon. There are atolls in tropical seas all over the world.
An atoll starts out as a small island of ordinary rock, often a volcano. Coral animals settle below the tide line, building a ring- shaped reef around the island. Then, through erosion or because of geological forces, the island slowly sinks down.
The coral reef, however, keeps growing. It grows almost to the surface as the land sinks, forming the distinctive ring shape. The shallow central lagoon (where the mountain used to be) usually has a floor of coral sand, studded with small patches of reef.

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Deepest Cave
Lechuguilla Cave, near Carlsbad, New Mexico, goes down at least 1,571 feet (479 meters), making it the deepest known cave on Earth. It is only partially explored, but already more than 97 miles (156 kilometers) of passages have been mapped.
The immense maze of rooms and passages that forms the Lechuguilla system was discovered in 1986. A group of spelunkers (cave explorers) decided to investigate a desert pit called Misery Hole. When they reached the bottom, they dug down and found a chamber from which a howling wind emerged, a sign of a large cave system.
Unlike most limestone caves that were formed by water dissolving the rock from above, Lechuguilla was formed by hydrogen sulfide gas coming up from underneath. The gas was released from an underground oil pocket because of geological shifts.

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Early Ocean Explorers
Long before Europeans set out to explore the world by sea, Polynesian explorers had sailed across thousands of miles of open water. They started as early as 1500 BC by exploring the nearby islands north of New Guinea, then sailed east and north to distant, unseen lands. By 1000 AD they had settled islands scattered across much of the vast Pacific Ocean.
The ancient Polynesians built sturdy double-hulled boats to carry colonists and all the animals, plants, and supplies that they needed to establish settlements. With time, they developed a sophisticated navigation system based on the positions of stars and the patterns of ocean swells.
By the time Captain Cook and other Europeans finally reached many of the remote islands of the Pacific, Polynesian people had been living there for hundreds of years.

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Electron Microscopes
Electron microscopes do not use light, and can show objects in much greater detail than any conventional light microscope. The detail is better because electrons are much smaller than light waves, and can be sent and detected with extreme precision.
There are several different kinds of electron microscopes. Two of the most frequently used types are transmission electron microscopes and scanning electron microscopes.
A transmission electron microscope (TEM) sends electrons through an extremely thin cross-section (slice) of an object and projects an image of the specimen onto a screen. Many organelles (the small structures which make up cells) were discovered with the help of transmission electron microscopes.
A scanning electron microscope (SEM) bounces electrons off a solid object in order to generate an image of that object's surface. The object is coated, placed in a vacuum chamber, and electrons are fired at it. The fired electrons "excite" electrons in the coating, causing them to be released. Sensors detect the ejected electrons, and a picture is constructed on a monitor screen.

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Evaporated Sea
Millions of years ago, the land at what is now the Straits Of Gibraltar rose up, blocking off the connection between the Mediterranean Sea and the Atlantic Ocean. Slowly, the sun did its work, and the Mediterranean Sea evaporated, leaving behind vast layers of salt and a few shallow salt lakes.
Geological changes continued at their slow pace. One day about five million years ago, the Atlantic Ocean finally burst through again, and a torrent of seawater began refilling the basin. Centuries later, the Mediterranean Sea was full again.
A very similar event happened around 5650 BC at the mouth of what is now the Black Sea. Once a freshwater lake, that body of water is now much larger, containing salt water that flooded in through the Bosporus.

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Expanding Lizard
When a desert chuckwalla (Sauromalus obesus) is disturbed, it runs into a rock crevice. If the threat persists, it puffs itself up with air, inflating its lungs up to three times their normal volume. It becomes tightly wedged in place, and almost impossible to remove from the rocks.
Chuckwallas are large lizards, closely related to iguanas, which can be up to 18 inches (46 centimeters) long. They are herbivores, with a special preference for yellow flowers. They are common in the southwestern US, where their favorite habitat (rocky hillsides) is still relatively undisturbed by humans.

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Giant Antlers
The largest antlers ever were those of the now extinct Irish elk. Their huge racks grew as large as 3.6 meters (12 feet) across, weighing more than 40 kilograms (88 lbs). Every year, they grew a whole new set from nubs on their heads.
These very large deer roamed across the northern hemisphere until about 10,000 years ago, when there was a sudden cold period called the Younger Dryas. When the climate got cold, the forests were replaced by tundra.
Recent studies suggest that although the Irish elk were still able to grow their huge antlers during the Younger Dryas, doing so depleted them of calcium and phosphorus. Unable to find enough food to restore themselves, they died out.
The largest antlers on living deer are found on the moose. Their antlers can get as large as two meters (over six feet) across.

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Giant Construction Project
There has never been a construction project as massive and expensive as China's Three Gorges Dam. This gigantic dam, which will be sixty stories high and 2.3 kilometers long (1.4 miles), will create a reservoir longer than Lake Superior. Scheduled for completion in 2009, the Three Gorges Dam is expected to cost $27 billion and will generate as much electricity as would 18 nuclear power plants.
The massive construction project is also highly controversial, and has generated domestic and international opposition. The reservoir it will create will drown many towns and villages, beautiful valleys, and historic sites. The ecosystem of the Yangtze River downstream of the dam will be permanently changed and some species may become extinct.

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Glass Shells
Diatoms (Bacillariophyta) are tiny, floating, one-celled life forms that build intricate shells out of silicon dioxide, the compound found in glass, sand, and rock crystal. Their minute shells are beautiful structures with very tiny details, and there are thousands of varieties.
The shell of a diatom has two halves called frustules. One of the frustules is slightly larger than the other, and they fit together tightly. Most diatom frustules are decorated with hundreds of tiny holes, grooves, or bumps, arranged in regular patterns.
Diatoms have been around for hundreds of millions of years. They are very important to Earth's ecology, producing about a quarter of all the free oxygen in the atmosphere. Although they may seem like plants, they have recently been assigned to a new kingdom, the Chromista, along with some other related life forms.

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Halogen Light Bulbs
Hot-burning "halogen bulbs" can last two or three times longer than regular bulbs because they are filled with chemically active halogen gases that preserve the filament.
The filament of an ordinary light bulb burns out because atoms of tungsten evaporate from its surface, so that it becomes thinner and thinner until it breaks. The evaporated tungsten is deposited on the inside surface of the bulb, where it forms a dark deposit.
The gas inside a halogen bulb combines with the tungsten atoms that condense on the glass, removing the deposit. When the combined molecules touch the hot filament, the tungsten is redeposited there, and the gas is released to do the same trick again.
Halogen bulbs don't last forever, though. Although the filament does not evaporate as fast, it does eventually develop thin spots, and the bulb burns out.

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Heavy Ice
Ice cubes made out of "heavy water" will not float in ordinary water.
Normal water is made of molecules containing one atom of oxygen and two atoms of hydrogen. Both of the hydrogen atoms in heavy water have been replaced by deuterium. An atom of deuterium is different from an atom of hydrogen in that it contains an extra neutron in its nucleus, making the whole atom almost twice as heavy.
Normal ice floats in water because its density is lower than that of water -- a result of its more open molecular structure. The extra mass of the deuterium atoms in heavy water adds enough weight that a heavy water ice cube sinks in ordinary water, although it still floats in heavy water.
Heavy water is used in nuclear reactors, where it slows down the fast neutrons emitted by the core and carries away the heat created there.

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Hops in Beer
The sharp bite of beer is partly a result of flavor elements that come from the conelike female flower of the hop vine (Humulus lupulus), also known as the "spices" of beer. But hops do much more than add flavor to beer.
Brewers began adding hops to beer in the fourteenth century, when it was discovered that not only was the flavor better, but the beer also held its head better (the foam lasted longer) and it was less likely to go bad during the brewing process.
Female hops flowers contain glands that produce resins vital to the brewing process. They change the surface tension of the liquid, so the head is firmer, and they also interfere with the growth of undesirable bacteria. Many complex compounds in the hops also contribute to the distinctive flavor of beer.

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Human Genome Size
You may have heard of the recently completed "human genome project," a monumental project undertaken to decode the entire DNA sequence of a human being (the human genome). Just how big is that sequence?
Each human cell contains 46 chromosomes, each of which is a DNA molecule wrapped around proteins called histones. If all the DNA molecules in one cell were unwrapped from the histones and stretched out end-to-end, the total length would be about six feet (2 meters). Almost every cell in your body contains six feet of DNA, wrapped up into a very compact space.
If all the information in the human genome were printed in small type, it would fill a thousand thick telephone directories. The whole sequence contains about three billion base pairs (the genetic equivalent of alphabet letters), including some 50,000 - 100,000 genes, each of which codes for a specific protein.

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Humming Fish
In the Pacific Ocean there are fish that make a loud humming sound. Sometimes the sound is so loud that it can be heard by people in boats on the surface. The sound is emitted in the spring and summer by thousands of male midshipman fish, who sit in rocky nests at the bottom.
The humming chorus is their way of attracting a mate, but not all male midshipman fish are hummers. There are two kinds. The larger kind are the ones who hum. The smaller ones, who are called "sneaker males," silently sneak into the nests of the hummers, depositing sperm there.
When a female midshipman fish visits the nest of a hummer male, she deposits her eggs, which are fertilized by sperm from the hummer male and from any sneaker males who have visited. The hummer male raises the brood, which may include several batches of young at different ages, from eggs deposited by different females.

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Insect Sweat
If you've ever lived where there are cicadas, you know that these extremely noisy insects make the most racket when it's blistering hot. How do they keep cool while remaining so active in the hot sun?
The secret is that cicadas sweat. These finger-long, winged insects have pores through which they secrete a watery liquid derived from the tree sap they drink. While they sing (by vibrating ridged membranes against their bodies), they sweat profusely, thus dissipating the heat of their efforts.
Those efforts result in the loudest sounds made by any insect. In Missouri in the summer of 1999, the din reached 85 decibels at some locations, louder than a large diesel truck at full power. Outdoor cafes had to close because the noise was too much for the customers.

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Largest Eyes
The eyes of the giant squid (Architeuthis dux) can be up to 25 centimeters (ten inches) across, about the size of a volleyball. Those large, sensitive eyes are useful in the dark waters where the giant squid lives, 200-700 meters (660-2,300 feet) below the surface of the ocean.
Giant squids are among the world's most mysterious megafauna (large animals). So far, no live specimen has been captured. They live in deep oceans all around the world, along with at least ten other species of very large squid.
Like other cephalopods such as octopi, giant squids have complex, well-developed brains. They are ferocious predators, but they are also pursued and eaten by large cetaceans such as sperm whales, some of which show the obvious scars of giant squid sucker disks.

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Largest Star
The largest known star is VV Cephei, a "red supergiant" in the constellation Cepheus. VV Cephei's diameter is 17.7 times the size of Earth's orbit. If it were put in the center of our solar system in place of the sun, it would extend almost to the orbit of Saturn, and it would swallow up Mercury, Venus, Earth, Mars, and Jupiter.
Like other supergiant stars, VV Cephei is a deep red color. It's also known as the "garnet star." It has a small companion star that circles it every 20.4 years. During one part of its orbit, the companion is hidden for about 1,000 days, and accurate measurement of that time makes it possible to calculate the main star's diameter.
VV Cephei is a massive star near the end of its life cycle. Astronomers believe that one day in the next million years or so it will explode into a supernova, releasing vast amounts of energy and leaving behind a tiny but massive black hole or neutron star.

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Light Catching Chemical
Green plants gather energy from sunlight and use it to build living tissue in a process called photosynthesis. (Oxygen is also produced, making plants the foundation of almost all life on Earth.)
Photosynthesis begins when chlorophyll molecules catch photons ("particles") of light. A chlorophyll molecule looks like a square plate with a long tail. When a photon strikes a magnesium atom at the center of the square, the atom releases a high-energy electron.
The electron is captured and sent along a complicated pathway. Along the way, its energy is collected and used to build sugar out of carbon dioxide and water.

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Light Catching Molecule
Green plants are the foundation of almost all life on Earth, because they collect the Sun's light energy and use it to build living tissue. They do it by catching photons ("particles" of light) with chlorophyll molecules in a process called photosynthesis.
A chlorophyll molecule looks like a square plate with a long tail. At the center of the square is an atom of magnesium. When a photon strikes the magnesium atom an electron is ejected.
The electron is then captured in the complicated molecular structure that surrounds the chlorophyll molecule. The energy it releases fuels a chemical reaction resulting in the creation of sugar molecules from carbon dioxide and ater.

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Microgravity Robot
Astronauts on missions in the Space Shuttle and the International Space Station will soon be joined by softball-size flying robots called Personal Satellite Assistants (PSAs). These spherical machines, now being designed in a NASA project, will move around in the weightless crew cabin under their own air-jet propulsion.
Each PSA will have a microphone, a camera, many sensors, and wireless data communications. A small flat-screen display will allow the PSA to serve as a self-positioning video conferencing tool, and it will be able to enter small spaces and send back a video feed of what it sees, hears, and senses.
The PSA is the first generation of a whole line of robotic assistants for space workers. We may also see "outdoor" construction robots to build large structures in the weightless vacuum of orbit.

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Milky Way's Shape
For many years, scientists thought that our home galaxy, the Milky Way, was a circular spiral galaxy like the nearby Andromeda Galaxy. But recently it has become clear that the Milky Way is a "barred spiral" galaxy.
Instead of having smooth spiral arms, our home galaxy has a nearly straight bar of stars across the center, with spiral arms trailing from the ends of the bar. The bar and the spiral bands are fuzzy collections of gas, dust, and millions of stars. Our sun is located at the edge of a spiral band, near one end of the bar.
The bar is not directly visible from Earth, because it is obscured by vast clouds of dust. Astronomers discovered it by carefully mapping the shape of the central bulge of stars in the Milky Way and by observing the motions of stars.
How do barred spirals form? One theory is that the bar is a consequence of intense magnetic fields near the center of the galaxy, which could cause the gas, dust, and stars to orbit differently.

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Momentum Exchange Tether
An orbiting spacecraft can send another one into a higher or lower orbit without using any fuel by simply reeling it out on a long string, then releasing it. This is called a momentum exchange orbital tether.
Momentum exchange tethers are different from the electrodynamic tethers described in another Cool Fact (linked below). No magnetic field is needed and no electricity is used, so they work around planets like Mars, which has almost no magnetic field.
One proposed system of tethers called the Lunavator would transfer spacecraft between the Earth and the Moon by flinging them along in relays, from one level of orbit to the next. The Lunavator could make Earth-Moon travel much more practical, and much less expensive.

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Most Islands in a Lake
Lake of the Woods, located at the corners of Ontario, Minnesota, and Manitoba, contains an estimated 14,000 islands, more than any other lake on Earth. It is also one of the most irregularly shaped lakes, with an estimated 65,000 miles (105,000 km) of shoreline.
During the last Ice Age, the land in that area was covered by a thick layer of ice. The ice scoured the surface, leaving many depressions and hills. Today, the depressions are filled with water, and a broad section of central Canada is sprinkled with thousands of small lakes.
Around 7000 BC, Native Americans hunted in the area. Throughout the region there are pictographs (rock art) from the Cree tribe, made about 500 years ago. The first white man to see the lake was the French explorer Jacques De Noyon in 1688.

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Muddiest River
The largest amount of sediment is carried by one of the world's largest rivers, China's Hwang Ho (Yellow River). The Hwang Ho used to carry vast amounts of yellowish silt into the Yellow Sea, but changed its course during a disastrous flood in 1852 and now empties into the Gulf of Chili, 400 miles further north.
This 3,000 mile-long river (4,800 km) receives most of its silt load as it passes through an area of loess (deposits of silt or clay, originally created as windblown dunes) just south of the Great Wall.
China has repeatedly attempted to control the Hwang Ho, but the river, also known as "China's Sorrow," has not responded well. Reservoirs and dredged beds fill with silt, and devastating floods are still common.

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Nest Impostor
The cuckoo bird does not make its own nests. Instead, the female finds a nest that has eggs in it, and lays one egg in it. The birds that made the nest seldom notice the extra egg. This practice is called "brood parasitism."
Cuckoo eggs hatch quickly. When the cuckoo chick emerges, the first thing it does is push all the other eggs out of the nest. If they hatch before it can do this, it pushes the babies out too.
The cuckoo chick, which is dutifully fed by its hosts, grows quickly, often to a size much larger than both of them. The hungry chick makes so much noise that the "foster parents" feed it generously.

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New Kinds of Planets
Astronomers are finding more and more planets orbiting stars outside the solar system. Many of these "extrasolar planets" are quite strange.
One group is the "hot Jupiters." These are super-giant planets several times the size of Jupiter, in very close orbits around their stars. Some of them are in orbits much smaller than Mercury's orbit around our Sun.
There are also planets that have very eccentric orbits, swinging in close to their star and then coasting out very far away. There are many other odd planets, including at least two that orbit around neutron stars.
As more strange, new planets are discovered, astronomers are scrambling to come up with explanations for how they came to be. Existing theories of solar system formation simply do not cover such oddities. There are many new theories.

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Nimble Insects
If you have ever tried to catch a cockroach, you know the little devils are fast and sure-footed. A team of biologists recently discovered that cockroaches can change course as many as 25 times in one second, making them the most nimble animals known.
Cockroaches can run as fast as one meter (over three feet) per second. The researchers were curious how these darkness-loving insects managed to avoid running into obstacles, so they built a special enclosure and filmed them at 250 frames per second.
They discovered that the roaches kept the tips of their antennae in contact with barriers, and were able to twist and turn very rapidly to follow the walls. Even when the insects were blindfolded with dabs of wax, they still kept a sure course around obstacles.

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Ocean Creatures
One of the most ancient creatures in the ocean is the hagfish, which remains virtually unchanged over its 300 million year history. This primitive, boneless agnathan (jawless fish) looks similar to an eel, but without visible eyes.
The hagfish is a scavenger that consumes dead creatures whose bodies have sunk to the sea floor. When threatened, a hagfish can emit up to a gallon of a syrupy, toxic slime, that makes it almost impossible to capture.
There's only one problem with all that slime: the hagfish needs a way to get rid of it after escaping the predator. It does this by tying its own tail in a knot, then sliding the knot all the way up past its head. When the knot pops off its head, it slips out of the slime and swims away.

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Ocean Walking Insect
The only insects known to live directly on the surface of the open ocean are the sea skaters (genus Halobates), close relatives of the water striders that walk on the surfaces of ponds and streams.
Like the water striders, sea skaters have waxy hairs on their feet that repel water, allowing them to stand on the surface tension. They are delicate insects with long legs and highly coordinated reflexes, enabling them to move around with great precision on the surface of the waves.
Sea skaters are predators, able to sense the presence of small swimming creatures just under the surface and spear them with their sharp mouthparts. They also eat insects that fall onto the water surface. Of course, they are themselves prey to any fish that is fast enough to snatch them.

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Oldest Stars
Our galaxy's oldest stars are also the smallest and the most abundant, numbering 70% of the galaxy's stars. They are red dwarfs, dim stars that are difficult to even see. Some of these stars formed more than ten billion years ago, and many of them are part of ancient globular clusters, spherical collections of stars that are found in a large halo around the galaxy.
Red dwarfs live a long time because they burn slowly. Without a large mass of gas, they are not able to create a high temperature and pressure in their cores where the fusion reactions take place, so the hydrogen fuses very slowly.
Objects that gather even less mass than a red dwarf do not generate enough internal pressure and heat to begin fusion. Unable to "light up," they become brown dwarfs, destined to fade into invisibility and become cold, dark balls of frozen gas.

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Penguin Boat
Instead of a propeller, the penguin flipper boat uses a pair of paddles at the back that look and move like the flippers of a penguin. The twelve-foot boat, invented by James Czarnowski, is called "Proteus."
The penguin flipper boat uses 17% less power than an equivalent propeller-driven boat, and produces far less turbulence and noise. It might be good for use in nature preserves, where propellers might cause too much disturbance of the ecosystem.
For inspiration Czarnowski watched the penguins swimming underwater at Boston's New England Aquarium. He mapped out the way they moved their flippers, and designed a mechanical system to mimic it, moving the paddles side to side while turning them at the same time.

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Prehistoric Creatures
Although science has not found a definitive answer to this question, it is considered likely that the first animals on land were eurypterids, primitive creatures very similar to today's scorpions. Fossil evidence indicates that they emerged from swamps during the early Silurian Period about 440 million years ago, approximately 200 million years before dinosaurs first appeared.
Eurypterids were among the most successful lines of early arthropods (animals with external skeletons). Some were giant ocean-dwellers, as large as 2.3 meters (7 feet). As one would imagine, they were quite formidable predators.
The first eurypterids to venture onto land didn't find very much there. Plants had only made it to land a short while before, also during the Silurian Period, and hadn't evolved much beyond mosses and other simple plants.
Today's scorpions are direct descendants of the ancient eurypterids, and have a very similar anatomy.

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Protein
The largest known single-chain protein is found in muscle cells, and is referred to by two names: titin and connectin. This huge molecule helps to maintain resting tension in muscle tissue and takes part in the contraction of muscle fibers.
A molecule of titan can be nearly one micron long (0.000001 meter or 0.00004 inch); which is bigger than some cells. Each molecule consists of about 30,000 amino acids (the basic building blocks of proteins).
Scientists have recently used "optical tweezers" to study titin by carefully stretching individual molecules. They found that a molecule of titin is something like a series of springs connected by looser chains, allowing it to stretch and return to its original shape easily.

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Robot Community
A scientist at the MIT Artificial Intelligence Lab has built a colony of microrobots. The tiny machines, which are called "ants," are only 1.4 inches (3.5 cm) long. They have tractor treads, long feelers, and jaws in front that they use to pick up their "food." They can communicate with each other by sending and receiving infrared signals.
The microrobots live on a big, flat surface called the "ant farm." They are learning how to play social games like "Follow The Leader," "Tag," and "Capture The Flag."
Each "ant" has its own microprocessor (computer chip), running software written in a style called "Subsumption Architecture," in which complex behavior is built up from collections of simpler behaviors that interact. As new levels of software are written, the robots will be able to do more complex things.

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Rock Varnish
Rocks that have been exposed to the harsh conditions in the desert often develop a hard, usually dark brown coating called "rock varnish" or "desert varnish". By examining the varnish coat, it is possible to measure how long the rock's surface has been undisturbed. Varnish can also form on the surface of desert soil, if it has been undisturbed for thousands of years.
"Rock varnish" is composed of oxides of iron and manganese, together with clay particles, cemented together by living bacteria. It tends to become darker with time. Some varnished rocks that have been untouched for tens of thousands of years are nearly black.
Native Americans used hard stones to scratch pictures in the dark varnish coating, allowing the natural light-color of the rocks beneath to come through. These durable images, called petroglyphs, can be seen throughout the American southwest.

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Rotary Rocket
The Roton Rotary Rocket not only has blades at the top, like the blades of a helicopter, it also has a rocket motor at the bottom that spins. It's a design for a fully reusable, manned, Earth-to-orbit spacecraft that only uses one stage.
The spinning rocket motor is more efficient than an ordinary rocket because no complicated, heavy fuel pumps are needed. The spin of the rocket motor causes the fuel to flow out toward the nozzles, where it mixes and burns.
On re-entry, the helicopter-like blades at the top are deployed. At first they spin passively, slowing down the craft as it enters the atmosphere. But later, small rockets at the tips of the blades are ignited, and the rotary rocket becomes able to hover and make a delicately controlled soft landing, tail first.

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Round Portholes
Portholes on ships are round for the same reason that submarine hatches have round corners and airliners have rounded windows. In all these cases, the vehicle is subject to flexing and mechanical stress. If the windows had sharp corners, the stresses would concentrate there, resulting in material fatigue and eventually cracking. With round or rounded windows, the stress is evenly distributed.
Large boats like cruise liners can have rectangular picture windows in some places because the local stresses there are smaller.
Some early commercial airplanes had large, rectangular windows, and the skin of the planes had a tendency to crack at the corners. Today's pressurized airliners have much smaller, rounded windows.

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Scale Eaters
Fish in the genus Perissodus eat mouthfuls of scales from the sides of other fish. These strange predators live in Africa's Lake Tanganyika, where they form part of one of the most diverse freshwater ecosystems on Earth.
Each Perissodus individual is left-biting or right-biting. Its mouth curves to the left or to the right, and it can only steal scales from one side of its prey. The number of left-biting and right-biting fish is roughly equal.
The scale-stealing Perissodus are cichlids, part of a family of fish that became isolated in Eastern African lakes millions of years ago. The family includes hundreds of specialized kinds of fish, with many different feeding and breeding habits. All of them evolved since the lakes were isolated.

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Shrinking Compound
Heating increases the motion of atoms, causing most substances to expand, but a ceramic called zirconium tungstate shrinks. One of the few known "heat shrinking" compounds, it shows this strange behavior over the widest range of temperatures, from near absolute zero (-273C or 460F) up to a red-hot 777C (1431F)!
Zirconium tungstate shrinks because of the unusual way in which its oxygen atoms are bonded. When they vibrate they tend to pull the zirconium and tungsten atoms closer together, causing the substance to shrink.
"Materials scientists" are looking for useful ways to use zirconium tungstate. One idea is to mix it with other compounds to create materials that do not shrink or expand with changing temperature.

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Sinking Ground
In Arizona, California, and hundreds of places throughout the world, the ground has been sinking for years. Some places in California's Imperial Valley have subsided more than 25 feet in the past century. Why is the ground sinking?
In almost all cases, ground subsidence is caused by the removal of fluids from beneath the ground, allowing the rock layers to settle and compress. It is usually caused by removal of groundwater, but sinking ground can also be caused by the removal of oil or even natural gas, or by the draining of wetlands.
Ground subsidence is a growing problem in many places. Deep fissures can form, cutting across roads, farms, and buildings, and the land can slowly tilt. The only solution is to stop drawing out groundwater, which becomes less likely as people around the world continue to face increasing water shortages.

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Slow Heart
Throughout the animal kingdom, there is a general relationship between an animal's size and how fast its heart beats: the larger the animal, the slower its heart beats. An adult blue whale with a heart the size of a small car has one of the slowest heart rates of all.
Researchers have been able to record whale heartbeats directly by listening to them from inside of submarines. When it is at the surface, a whale typically has a heart rate of about five or six beats per minute. When it dives, the whale's heart slows down to about three beats per minute.
The whale's heart slows down when it dives in order to save oxygen, and to keep the precious substance in the central body rather than letting it get used up in the fins, skin, and other outer body parts.

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Smart Birds
Ravens and their smaller cousins, crows, are among the smartest birds. Not only can they untie knots, they can also unzip zippers and unfasten velcro. Ravens have a highly sophisticated language with hundreds of distinct sounds. They are highly social birds, who mate for life and play complex games with each other.
Ravens are the largest perching birds. They can have up to a four- foot (1.2 meter) wingspan, and they are powerful fliers with tremendous endurance. They live all around the northern hemisphere, from tropical jungles to the snowy wastes of the high Arctic. Their high intelligence and endurance give them the ability to adapt to many conditions and eat a wide variety of foods.
For years ravens were thought of as pests in the United States. They were seen as thieves of eggs and small barnyard animals, and shot on sight. Their numbers declined steadily until recently, but now they are recovering across the western and northern states, learning to coexist with the humans who were once their main enemy.

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Spherical Fish
A pufferfish responds to stress by gulping a huge amount of water, expanding itself in a few seconds into a hard ball three times as large as the resting fish. Some species have sharp spines that pop out straight when the fish puffs up, making them particularly nasty if eaten by a predator.
When it puffs up, a pufferfish's stomach expands to 100 times its normal volume. Its abdominal cavity is lined with folded, pleated tissue, and some of its ribs are missing, making it easier to inflate. Its skin is threaded with thousands of fibers that snap tight when it is fully inflated.
Pufferfish are relatives of sunfish and triggerfish. They are awkward looking fish, with a boxy shape, and they do not swim very well. They rely on their unusual defense (and recognition by predators) to protect them.

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Sunken Continent
In the southern Indian Ocean, about 4000 kilometers (2500 miles) southwest of Australia, there is a very large undersea plateau called Kerguelen. In the last 110 million years, Kerguelen has risen above the waves and re-submerged three times.
Scientists discovered Kerguelen's past by examining deep core samples and reconstructing the movement of the Earth's crustal plates. Kerguelen rose above the water about 110 million years ago, then submerged. The land rose again 85 million years ago, and broke the surface once more 35 million years ago.
Scientists believe the force that lifted the sunken continent was generated by gigantic injections of volcanic magma deep beneath the Earth's crust. When the underground activity subsided, the plateau sank again.

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Sun's Core
The temperature at the sun's core is thought to be about 15 million degrees C (27 million degrees F), by far the hottest temperature in the solar system. The material there is plasma, a gas of electrons and atomic nuclei, compressed to about ten times the density of lead.
The sun's nuclear fusion reactions only happen in the innermost core, where the pressure and temperature are high enough to fuse hydrogen into helium. The energy generated there starts out as high energy gamma rays and x-rays, not as visible light.
The energy released by fusion makes its way out from the core through several layers, colliding with the dense plasma all the way. It takes about a million years for each photon (energy "particle") to reach the surface of the sun. By that time the energy has been divided and down- shifted by collisions, until it's mostly visible light.

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Swimming Ants
The only known swimming ants live in the tendrils of a pitcher plant called Nepenthes. The ants swim around in the digestive fluid that collects inside the plant's insect-trapping pitcher leaves. The ants avoid being digested by the juices the plant secretes, although how they do this is not understood.
When a large insect falls in and drowns, the ants pull it out of the water and eats it. By pulling out large insects, the ants keep the pitcher from being fouled by too many decaying insect bodies. But small insects are allowed to decompose in the water, where their substance can be absorbed by the plant.
The pitcher plant benefits from this arrangement because its digestive fluid is kept fresh and pure, and the ants also protect it from insect pests. The ants get a safe place to live and a regular supply of insects to eat.

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Thickest Skin
The thickest skin in the animal kingdom belongs to beluga whales (Delphinapterus leucas), the beautiful white whales found in the Arctic Ocean. Their skin can be as thick as 1 centimeter (0.39 inch). By contrast, the thickest human skin is only 2.5 millimeters thick (0.1 inch).
Unlike other whales, belugas go through an annual summer molt, during which they shed the outer layers of their skin. During the molt, they rub themselves on gravel beds or other rough surfaces, exposing fresh, pure white skin.
In the Inuit language, the thick skin of beluga whales is called muktuk. Muktuk is an important part of the Inuit diet, because it contains as much vitamin C as oranges, more than any other animal source.

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Tree Kangaroos
In the rain forests of New Guinea and northern Australia, there are kangaroos (in the genus Dendrolagus) that live in trees.
Although they are adept at climbing, tree kangaroos can't move well on open ground, where they are not able to make more than two or three "kangaroo hops" at a time. Occasionally, they have been seen to make astounding leaps of up to 18 meters (59 feet) from trees to the ground.
Dendrolagus kangaroos eat leaves, fruits, flowers, and grass. Much of what they eat is not very nutritious, but their stomachs contain millions of tiny worms and bacteria that help break down their leafy diet.

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Twig Camouflage
Worldwide, there are almost three thousand species of stick insects (family Phasmitidae). These long, very thin, plant-eating creatures have evolved to resemble the stems of the plants they eat. Some Indonesian species can get up to a foot long (30 cm), making them the longest insects alive today.
Looking like a stick is great camouflage, but some stick insects take the disguise even farther. If they are too violently disturbed, they drop to the ground, playing dead. Some even "break" by releasing a leg or two.
Stick insects belong to the order Orthoptera, along with their relatives the grasshoppers, crickets, mantids, and cockroaches. Like other Orthopterans, stick insects hatch from eggs as nymphs that resemble the adult insects.

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Ultra-thin Layers
By using "molecular beam epitaxy," (MBE) technologists can create substances composed of many layers of different materials, in which each layer is only one molecule thick.
In MBE, a very clean crystal surface is placed in a high vacuum and chilled. Molecules are allowed to evaporate from a heated crucible, and they cling to the chilled crystal surface. It is possible to control conditions so well that layers one molecule thick are created.
Epitaxy is used in the manufacture of computer chips. Microscopic lasers and light sensors can also be built, making possible new kinds of computers based on light instead of electricity.

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Whale Ancestors
Until recently, no one knew what sort of animals evolved into whales because the only fossils of whale-like creatures were fully adapted to the ocean. Whales evolved from land-walking mammals, but what were they like?
Fossils discovered in 1983 in Pakistan helped to fill in this "missing link." The fossil skull of an animal called Pakicetus from 50 million years ago shows that whale ancestors were water-loving predators ranging from wolf-size to bear-size. They swam in shallow freshwater streams, and had ears adapted for listening underwater. Since 1983, even earlier whale ancestors have been discovered.
Another early whale was discovered in 1994. Called Ambulocetus, it was a marine mammal that swam by flexing its spine the way modern whales do. Analysis of oxygen in its bones suggests that it needed to stay close to shore because it had not yet developed the ability to drink salt water as modern whales do.

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