What about the notion that some animals can sense a quake before it happens? While scientists acknowledge that animals are more sensitive than humans to the first wave of energy a quake creates, we only have evidence that animals detect it seconds before humans feel the more powerful jolt that follows.
Where Did Earth’s Water Come From?
Our planet is wet. Seventy-one percent of Earth’s surface is covered in water. Most of that water is in the oceans, but another 3.5 percent is in rivers and lakes, locked up in the ice caps, or floating in the atmosphere in the form of water vapor. More fresh and salty water hides beneath the surface, and scientists have even discovered that Earth’s mantle is replete with the wet stuff. The watery nature of our home planet makes it unique. So where did all this water come from?
At least some of that water was here at the moment of creation. Scientists estimate that 30 to 50 percent of the water on Earth today originates from ice from the dust cloud that eventually coalesced into the Sun and its planets. Thanks to Earth’s mass, volcanism, and distance from the Sun, our climate now has the right temperature and atmospheric pressure for that ancient ice to exist in a state of liquid water (whereas on other planets, it either froze or outgassed back into space).
But where did the rest come from? For years, the most obvious source was comets—miles-wide snowballs that roam the solar system and could have bombarded the planet in the first billion years. Recent spectrographic observations of comets that buzzed Earth, and the latest findings from the European Space Agency’s space probe, Rosetta, point in another direction. The spectrographic signature of the water of these objects indicates higher levels of heavy water—water with deuterium rather than ordinary hydrogen—than is found on Earth. Other findings from Rosetta indicate the presence of a bluish hue on part of one comet known as 67P/Churyumov-Gerasimenko, which would suggest the presence of frozen water beneath the surface of dust and rock. So, if not comets, what and where did our water come from?
The process of elimination leads us to asteroids or, more specifically, a class of meteorites called chondrites, which originated from space rocks in the inner solar system. These potential candidates harbored water on their surface without releasing it, thanks to the younger and cooler Sun, depositing the moisture.
800,000 years ago, a compass facing what we now call “north” would point to “south.” This is because a magnetic compass is calibrated based on Earth’s poles. The N-S markings of a compass would be 180 degrees wrong if the polarity of today’s magnetic field were reversed.
Why Do Earth’s Magnetic Poles Flip?
Earth’s magnetic poles have flipped many times over the last billion years, switching magnetic north to Antarctica and magnetic south to the Northern Hemisphere. Geologists can see the evidence of reversals in the rock, but clues to how they happened or why are elusive. On average, the magnetic field reverses every 200,000 years. However, the time between reversals varies significantly. The last time the field flipped was 780,000 years ago. So are we headed for a flip anytime soon?
Most scientists believe a theoretical phenomenon, called the geodynamo, sustains Earth’s magnetic field. However, aside from somehow drilling 4,000 miles (6,437 km) into Earth’s center, there is no way to observe the process. Using a computer model, scientists Gary Glatzmaier and Paul Roberts at the University of California describe what they believe are the forces that create and maintain the magnetic field. Deep inside the planet, the inner core rotates underneath a liquid outer core made of iron and nickel. The churning acts like convection, which generates electrical currents and, subsequently, a magnetic field. “Once in a while a disturbance will twist the magnetic field in a different direction and induce a little bit of a pole reversal,” Glatzmaier told. These instabilities constantly occur in the fluid flow of the core, tracking like a hurricane through Earth’s core, only moving at a snail’s pace. Scientists can now pinpoint the boundary where these instabilities in the magnetic field occur. Currently, scientists are following a disturbance in the east-central Atlantic Ocean moving toward the Caribbean.
Earth’s magnetic field shields most parts of our planet from charged particles in space, mainly from the Sun. Instabilities, like the one moving toward the Caribbean, cause Earth’s magnetic field to weaken. Today, it is about 10 percent weaker than when German mathematician Carl Friedrich Gauss first measured it in 1845. Most scientists believe this weakening could lead to a field reversal, but fossil records show it has had no significant effect on living organisms. We may experience more cosmic rays penetrating Earth’s atmosphere, and observers might see the aurora borealis at all latitudes. Birds that rely on the magnetic field to fly could become confused. However, as long as the field remains strong enough, the effects should be minimal. And while a geophysicist might say the next big flip is coming “soon,” it could still be as many as 10,000 years away.
How Do Icicles Form Underwater?
In the coldest parts of the world’s oceans, icicles form on the surface and shoot down toward the ocean floor. They’re known as brinicles or sea stalactites, and scientists have only recently detected and begun to understand them.
In the winter, seawater begins to freeze in the extremely cold climates of the Arctic and Antarctic. As ice crystals form, salt in the water is separated from the freezing water. This brine collects in the solid ice in small pools and remains in the ice until it begins to crack. The cracking releases streams of the brine, which is denser and colder than the surrounding seawater. As the brine moves downward, it turns the water around it into a tube of ice that looks something like the stalactites that form on cave ceilings.
In 2011, a camera crew for the British Broadcasting Company filmed the formation of a brinicle for the first time. Some British media called it “the icicle of death,” because as it shot downward through the ocean and reached the bottom, it killed tiny sea creatures living there. Smaller sea icicles become feeding spots for other forms of sea life, which eat algae that cling to the brinicles. Andrew Thurber of Oregon State University is one of the few scientists who has seen brinicles form. Working underwater in a dive suit, he examined ones that attract swarming sea life to feed. He compared his experience to “swimming under a beehive. Thankfully, they don’t sting.”
CHAPTER 5
Other Life Forms
How Did Life Arise on Earth?
Questions about the origins of life are not only philosophical; many biologists, chemists and geologists struggle to find answers as well. Plants and animals represent just a fraction of the history of life on Earth, which began 3.8 billion years ago.
In fact, for most of the history of life on this planet, microorganisms like bacteria, protozoans, and algae ruled the roost. Homo sapiens emerged only 200,000 years ago, accounting for less than 0.004 percent of Earth’s history. Most scientists agree that life relies on natural selection and the ability to reproduce, and over the years evolution led us from simple beginnings to humankind. But understanding the origins of life takes some speculation.
Even the most basic living organisms like bacteria are complex compared to the first simple organic molecule that existed on Earth. The long strains of simple nucleotides were a composition of carbon, hydrogen, nitrogen, oxygen, and phosphorus atoms, known as RNA (the precursor to DNA). The living molecules could self-replicate the way all living things do, while natural selection gave different variants an advantage. Eventually a membrane evolved to surround the genetic material, which proved so advantageous that this type of molecule quickly out-competed its “naked” counterparts. Through natural selection, two-stranded DNA evolved from the simpler RNA into a more stable alternative. This organism similar to modern bacteria became the foundation to life on Earth.
Finding proof of where the first organic material came from isn’t the hard part. Stanley Miller at the University of Chicago conducted a famous experiment in the early 1950s. Combining methane, ammonia, hydrogen, and water in a beaker (essentially the same components t
hat were present in Earth’s early atmosphere), he inserted an electric charge simulating lightning. A few days later he found brown goo in the beaker, which turned out to be amino acids, or the building blocks of proteins. Meanwhile, Harvard biology professor Andrew Knoll wonders about the process of evolution from the simplest of organic material to the complicated living bacteria today. That is, how did life progress from a “warm little pond on primordial Earth that has amino acids, sugars, and fatty acids to something in which nucleic acids are actually directing proteins to make the membranes of the cell?” Somehow all the separate constituents must work together, but scientists are still unsure how that happens. The billions of years between the first sign of life on Earth and today’s complex living organisms remain elusive. However, if Miller’s experiment is valid, we know that Earth created life, and life changed Earth.
How Do Animals Sense Magnetic Fields?
Capable of returning home from a location more than 1,000 miles (1,609 km) distant, homing (also known as messenger or carrier) pigeons have been conveying diplomatic correspondence, news of great battles, and the results of Olympic contests since the days of Genghis Khan. How do they find their way home? The answer is a sense called “magnetoception.”
Magnetoception is the ability of organisms to sense magnetic fields. Many biologists believe it is the reason why homing pigeons can so reliably find their way home, why migratory animals can navigate vast distances, and perhaps even why some humans seem to have an innate sense of direction. But how animals can sense magnetic fields remains a mystery.
One hypothesis behind magnetoception suggests that animals capable of sensing magnetic fields actually possess small amounts of magnetite, a magnetic iron ore, and that perturbations of this internal magnetite help the navigating creature orient itself to magnetic north and south. The discovery of small amounts of magnetite in the beaks of pigeons helps to strengthen this claim.
Another hypothesis proposes that magnetoceptive animals sense the electric induction produced as they move through Earth’s magnetic field. Movement of conductive material through a magnetic field induces electricity, so if animals can sense the variations in electrical induction, they may very well be able to orient themselves to Earth’s magnetic field.
Perhaps the most promising hypothesis depends on chemical reactions that may take place in the eyes of magnetoceptive creatures. According to this hypothesis, proteins called cryptochromes produce chemical reactions that are essential to circadian rhythms and also to sensing magnetic fields. Proponents of this theory believe that, changes in the field affect the chemical reactions that cryptochromes are responsible for, yielding a chemical signal that can be subconsciously interpreted by magnetoceptive creatures. Such speculation is as yet unproven.
Starting on the southeast coast of the United States, loggerheadsea turtles hatch and begin one of the most epic migrationsin the animal kingdom, following the Gulf Stream acrossto Europe and down the western shore of Africa, thenreturn across the Atlantic Ocean. The solo journey coversan amazing 8,000 miles (12,875 km); the turtles returnto the starting point between 6 and 12 years later. Theloggerhead turtles take on the difficult migration withoutan external map or detailed directions. Scientists arestill unraveling the mystery of how they find their way.
How Do Animals Migrate?
Navigating is not the same for all species. Short-distance migration is primarily a search for food. Rocky Mountain elk travel a relatively short distance, on average about 15 miles (24 km), to the high alpine tundra in the summer to find lush resources, but retreat to the hills where food is more abundant during the harsh winter months. Along the way they use landmarks, like rivers, to guide them.
Long-distance migration is more complex, determined by the genetic makeup of a species. Arctic terns make the longest migration of any species, from the Arctic to the Antarctic and back—a round-trip of more than 40,000 miles (64,374 km). How they know where to go is mostly a mystery. While birds may be sensitive to the change in latitude, that doesn’t explain the accuracy of some migration patterns. Scientists believe birds use Earth’s magnetic field, which grows stronger the closer the birds fly to the equator. They time their circadian rhythm to the cycle of the Sun and use the stars to follow a north-south path. Landmarks also provide visual cues. It is probable that birds use several of these methods to calibrate against each other, ensuring they arrive at the same destination year after year.
Protecting stopover areas and winter destinations is key to helping species survive. The endangered loggerhead turtle has seen a resurgence in recent years, due in part to local conservation groups preserving and protecting nesting grounds from North Carolina down to Florida. Since many species travel the same path every year, conservationists are working hard to save important areas that are vital to migration and consequently to the survival of a species.
Why Do Cats Purr?
It’s a mystery as old as civilization and as inscrutable as the mighty Sphinx: Why does a cat purr? Despite decades of research, the function of the house cat’s purr remains unclear. We know cats tend to purr when we pet them and when they knead (massage soft objects with their paws). Some purr while eating. Some purr while nursing an injury. Some even purr while giving birth. Why would one particular bodily function evolve in response to so many disparate stimuli?
Natural selection implies that unique physiological characteristics evolve to improve an organism’s chances for survival. So how does purring improve cats’ ability to pass on their genes? Leslie Lyons, assistant professor of veterinary medicine at the University of California at Davis, cites evidence that sonic reverberations at the frequency of a cat’s purr—around 20 to 150 hertz—promote bone density and prevent muscle atrophy. House cats use purring as a way to solicit food from their keepers and to signal to their kittens that it’s time to feed. In these ways, purring helps cats survive and further their genetic line through their offspring.
However, neither of these theories explains why cats purr in response to both pleasure and duress. Some veterinary researchers, including Lyons, believe that the function of a cat’s purr is similar to a human’s tendency to smile, hum, sing, or whistle. We might do any of these things when we’re happy, but also when we’re nervous or unhappy. These behaviors release endorphins—hormones that make us feel pleasure. For cats, purring might release endorphins, either as an involuntary response to feeling pleasure or as a semi-voluntary means of relaxing when stressed.
In addition to the mystery of why remains the mystery of how. Despite extensive research, scientists and veterinarians have yet to identify a unique organ responsible for producing the purr.
Many species are attracted to bright colors in their mate’s appearance.
Why Do Ducks Have Orange Feet?
Actually, many species of ducks have feet and legs tinted a bluish green or gray. But for the ducks that do strut around on orange feet—well, it’s all about attracting the ladies. Chicks dig orange.
Kevin Ornland is an evolutionary biologist at the University of Maryland at Baltimore County, and he knows as much about mallard-duck coloring patterns as anyone; it was the topic of his graduate thesis. “I looked at male mallards and thought, gosh, they exhibit so many wonderful colors; I wonder which ones females care about,” he says. Do lady ducks lust after the males’ green head plumage? Or maybe it’s the blue patches on the males’ wings? Then again, what female duck can resist a nicely proportioned set of white “necktie” feathers? After four years of documenting mallard courtships, Ornland found that none of those features mattered. All the female ducks cared about was the brightness of the guy’s yellow-orange bill.
Bright orange coloring suggests that a male duck, also known as a drake, is getting all his vitamins, particularly carotenoids, such as beta-carotene and vitamin A, which are antioxidants that can be beneficial to the immune system. “This indicates that his behaviors and genes are good enough for him to recognize and eat the right food, or that his
immune system is strong enough to produce bright orange legs,” Ornland says. “The female sees this as a very attractive trait to pass on to her offspring.”
Ornland’s work only looked at drakes’ bills, but he thinks there’s enough circumstantial evidence to confirm that ducks check out each other’s feet, too. “Blue-footed boobies have, obviously, very blue feet, and it’s very well documented that they use their feet in courtship and that females do care about the coloration of males’ feet,” Ornland says. “Perhaps mallards, like the boobies, have a foot fetish.”
The 2014 Ebola epidemic in West Africawas the largest in history and launchedthe spread of isolated cases incountries that had never beforeseen people sickened with the virus.
Will Disease Drive Us All to Extinction?
Virulent infectious diseases and parasites have long been shown to be a significant cause of decline in biological populations. But can disease lead to the actual extinction of the host species—such as humankind?
Scientists attempt to determine the extinction-threatening effects of disease by first studying its role in historical extinctions. But proving that infectious disease is responsible for past extinctions is tricky business. After all, the extinct species is not around for scientific investigation. Even if a pathogen or parasite were discovered in a disappearing population, it would not prove that the pathogen itself was responsible for the decline.
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