Paleontology - Real-life applications



Our Place in the Grand Scheme of Things

All areas of historical geology—including paleontology—are concerned with geologic time, a term that refers to the great sweep of Earth's history. This is a timescale that dwarfs the span of human existence, and to study the history of life on Earth, a mental adjustment of monumental proportions is required. One must discard all notions used in studying the history of human civilization, including such concepts as modern, medieval, and ancient, which are essentially useless when discussing geologic time.

Human civilization has existed for about 5,500 years, the blink of an eye in geologic terms. Even the span of time since the first appearance of the genus Homo (to which humans, or Homo sapiens, belong), is minuscule: 2.5 million years compared with 4.6 billion years, or about 0.04% of the planet's history. A couple of analogies, one to a shorter span of time and another to a measurement of space, will help us understand the scope of time encompassed in the evolution of species.

LIFE APPEARS IN JUNE—SO TO SPEAK.

Suppose that the entire history of Earth were likened to a single year of 365.25 days, starting with the formation of the planet from a cloud of dust and ending with the present. At what point in the year would the first aerobic life-forms appear? We are not talking about anything approaching a human or even a clam or a fern or a piece of algae—just a single-cell organism that depends on oxygen for energy.

One might guess that such life-forms appeared sometime in January, or at least by the end of winter in late March. In fact, the first aerobic single-cell life-forms arose around June 15—nearly halfway through a year. Even at about the time of Thanksgiving, the most complex organisms would be fish and a few early amphibians.

We tend to associate the dinosaurs with the early phases of Earth's history, but this only illustrates our distorted view of geologic time. In fact, the Jurassic period would be analogous to a period of about five days from December 15-20. By Christmas Day, all remaining dinosaurs would have been headed toward extinction, their dead bodies eventually forming the fossil fuels that power present-day civilization.

By this point we are within a few days of the year's end, and yet nothing remotely resembling a human has appeared. Our own genus would not come on the scene until around 8:00 P.M. on December 31. The New Year's Eve countdown would be nearing by the time human civilization began, at about 42 seconds before midnight. Christ's birth would have occurred at about 14 seconds before midnight, and the final 10-second countdown would begin about the time the Roman Empire fell. The life span of the average person would correspond to approximately half a second or less.

ANOTHER ANALOGY: LOS ANGELES TO NEW YORK.

To use another analogy, suppose we are driving from Los Angeles to New York City, and that this distance corresponds to Earth's history. Once we reach western Nebraska, with about 46% of the distance behind us, we would come to the beginning of the Proterozoic era and the origins of aerobic life-forms. One might wonder why "nothing" happened on all those long miles from L.A. through the deserts, mountains, and plains of the western United States, but as we have seen, a great deal happened: Earth formed from a cloud of gas, was pounded by meteors, and gradually became the home to oceans.

The end of the Proterozoic era (about 545 million years ago) would be at about 88% of the distance from Los Angeles to New York—some-where around Pittsburgh, Pennsylvania. By this point, the continental plates have formed, oxygen has entered the atmosphere, and soft-bodied organisms have appeared. We are a long way from Los Angeles, and yet almost the entire history of life on Earth, at least in terms of relatively complex organisms, lies ahead of us.

If we skip ahead by about 339 million years—a huge leap not only in time but also in biological development—we come to the point when the dinosaurs appeared. We are now 95% of the way from the beginning of Earth's history to the present, and if it is measured against the distance from Los Angeles to New York, we would be somewhere around Scranton, in eastern Pennsylvania. Another 89 mi. (142 km) from the Scranton area would put us at a point about 65 million years ago, or the time when the dinosaurs became extinct. We then would have less than 40 mi. (64 km) to drive to reach the period where genus Homo appeared, by which time we would be in the middle of Manhattan.

Compared with the distance from L.A. to New York, the span of time that Homo sapiens has existed would be much shorter than the drive from Central Park to the Empire State Building. The entire sweep of human civilization and history, from about a thousand years before the building of the pyramids to the beginning of the third millennium A.D. , would be smaller than a city block. It is much smaller, in fact—close to the size of a modest storefront, or 15.54 ft. (5 m).

How Did We Get Here?

On the one hand, the history of relatively complex life-forms is relatively short compared with Earth's history; on the other hand, it is unbelievably long, when one considers the diversity of forms that have evolved in the past half-billion years. What follows is an extremely brief overview, touching on a few points in the development of life on Earth.

The discussion here is far from comprehensive, the purpose being not to provide a detailed overview of evolutionary processes but to illustrate the evolution of life-forms by a few examples. The reader is strongly encouraged to consult a textbook or other reliable information source for greater illumination of these particular topics. Along with this overview, we look at some of the more dramatic aspects of paleontologic study: dinosaurs and mass extinction.

The fossilized history of life on Earth really began in earnest only with the Cambrian period, which saw an explosion of invertebrate (without an internal skeleton) marine forms. These dominated from about 550 to about 435 million years ago. At the latter point, the boundary between the Ordovician and Silurian periods of the Paleozoic era, there occurred the first of five major mass extinctions, as the "supercontinent" of Gondwana crossed the South Pole, freezing most life-forms that were then alive. As always happened with these mass extinctions, some life-forms survived, and within a few million years life again was thriving.

COMING OUT OF THE WATER.

One of the favorite subjects of modern cartoonists is the migration of creatures from the water to the land. For example, following the enactment of stiff airport security guidelines in the wake of the September 11 terrorist attacks, a New Yorker cartoon in late 2001 showed this evolution from fish to amphibian (a creature that can live both in the water and on the ground) and, ultimately, to the human being. Then, in the last evolutionary sequence, Homo sapiens is depicted in a business suit, going through an airport security scanner. Most cartoons based on this event in paleontologic history follow a common theme, which can be summed up thus: "We went through all that evolution just for this ?"

Certainly, the transition from water to solid ground was a massive step—one of almost inconceivable importance. This invasion of the land, which probably took place about 400 million years ago, perhaps started when fishes of the Devonian period (named after Devonshire in England) began breathing oxygen near the surface of shallow waters. In time they made their way onto the land, and as the number of species grew, their lobed fins developed in different ways for different groups of fish, at length becoming the many limbs and appendages specific to large groups of species, such as birds or mammals. This may seem a bit far-fetched, but even today catfish are known to pull themselves out of the water and onto land if a specific need to do so arises.

Why did the first fish leave the water? Perhaps because the water levels were receding, as they have done periodically in the course of Earth's history as a result of massive freezing of global water supplies—that is, ice ages. Whatever the reason, we can be sure of the fact that the fish were not in any way attempting to reach some "higher" state of development, nor was any force pushing them to "evolve." Therein lies one of the major misconceptions about evolution, even among many of its adherents. The very name evolution is somewhat unfortunate, because it suggests that life-forms are moving gradually toward a state of heightened development. Instead, they simply are adapting to circumstances that confront them; hence, the entire phenomenon might well be called by the much less dramatic-sounding name adaptation.

Mass Extinction

Let us now pause in our narrative to discuss examples of a phenomenon that has been mentioned several times already: mass extinction. One of the truly amazing things about the history of life on Earth is the way in which forces have seemingly conspired to wipe out virtually all living things, not just once but at least five major times, along with a number of more limited instances.

Over the course of Earth's history—even its very recent history—numerous species have become extinct, usually as a result of their inability to adapt to changes in their natural environment. In the extremely recent past (recent geologically, that is—since the end of the last ice age about 10,000 years ago), some extinctions or endangerments of species have been attributed to human activities, including hunting and the disruption of natural habitats. For the most part, however, extinction is simply a part of Earth's history, a result of the fact that organisms incapable of adaptation soon die out. This is the infamous "survival of the fittest," an aspect of evolutionary theory that many a social or political ideologue has misappropriated for the purpose of insisting that one particular ethnic or social group is naturally superior to another (see Evolution).

Why does mass extinction occur? As we noted earlier, one possible cause of mass extinction is a sudden and dramatic change in ocean levels. Other causes include volcanic eruptions or the effects of events or objects from space—the explosion of a star, perhaps, or the impact of a meteorite on Earth. Although scientists have a reasonable idea of the immediate causes of mass extinction in some cases, their understanding of the root causes still is limited. This fact was expressed by the University of Chicago paleobiologist David M. Raup, who wrote in Extinction: Bad Genes or Bad Luck? : "The disturbing reality is that for none of the thousands of well-documented extinctions in the geologic past do we have a solid explanation of why the extinction occurred."

THE GREAT FIVE MASS EXTINCTIONS.

The five largest known mass extinctions occurred at intervals of between 50 million and 100 million years over a span of time from about 435 million to 65 million years ago. The first of them we have mentioned as perhaps being associated with the first migrations of organisms to land. This was at the end of the Ordovician period, about 435 million years ago, when a drop in the ocean level wiped out one-fourth of all marine families. No wonder some of the fish adapted to life on land!

Changes in sea level along with climate changes also appear to have brought about the second great mass extinction, which we also have mentioned, near the end of the Devonian period, about 370 million years ago. But no biological cataclysm in Earth's history can compare to the mass extinction that attended the close of the Permian period some 240 million years ago—an event so traumatic to life on Earth that it has been dubbed the great dying.

Imagine if 96% of all people alive today were killed—a staggering and terrifying concept. This would be far more fatalities than the combined death toll of both world wars; the Black Death of 1347-1351 and the influenza epidemic of 1918-1920; the various Nazi, Stalinist, and Maoist acts of genocide; and all major earthquakes and other natural disasters in history. Now imagine that along with all those people, 96% of all other life-forms—plants and trees, birds and fishes, single-cell organisms and the

DINOSAURS DOMINATED EARTH FOR A PERIOD OF MORE THAN 100 MILLION YEARS, ENDING ABOUT 65 MILLION YEARS AGO. THE FLYING TRICERATOPS, A CREATURE OF THE LATE CRETACEOUS PERIOD, MAY HAVE BEEN A LINK BETWEEN DINOSAURS AND BIRDS. (© Kevin Schafer/Corbis. Reproduced by permission.)
D INOSAURS DOMINATED E ARTH FOR A PERIOD OF MORE THAN 100 MILLION YEARS , ENDING ABOUT 65 MILLION YEARS AGO . T HE FLYING T RICERATOPS , A CREATURE OF THE LATE CRETACEOUS PERIOD, MAY HAVE BEEN A LINK BETWEEN DINOSAURS AND BIRDS . (
© Kevin Schafer/Corbis
. Reproduced by permission. )
like, which vastly outnumber the relatively small human population of Earth—all ceased to exist as well. Such was the almost incomprehensible scale of the so-called great dying, an event whose cause has not been determined, though it may have resulted from a volcanic eruption in Siberia.

The Age of the Dinosaurs

Now that we have mentioned only three of the five great mass extinctions, it is appropriate to discuss the creatures that died in the fourth and fifth: the dinosaurs, or "terrible lizards." Though they were the most well-known creatures of the Mesozoic era, which lasted from about 240-65 million years ago, dinosaurs were far from the only notable species on Earth in that phase of geologic history. In fact, it was during the first period of the Mesozoic era, the Triassic, that a group of creatures destined to make a greater impact on Earth—mammals—first appeared. During this time, botanical life included grasses, flowering plants, and trees of both the deciduous (leaf-shedding) and coniferous (cone-bearing) varieties.

Backtracking just a bit, at the beginning of the Devonian period, about 410 million years ago, the first vertebrates (animals with an internal skeleton) made their appearance in the form of jawless fishes. Plant life on land consisted of ferns and mosses. Then came the late-Devonian mass extinction we have mentioned, which removed many of the newly evolved invertebrates, including most fishes. By the end of the Devonian, about 360 million years ago, fish had evolved jaws, and life was thriving on land. Among these life-forms were reptiles in the animal kingdom, and gymnosperms, or plants that reproduce sexually by spreading exposed seeds—a primary example from our own time being pine trees.

MONSTERS OF THE MESOZOIC.

Although the existence of dinosaurs has been an established fact for as long as anyone alive can remember, we have had knowledge of them only since the mid-nineteenth century. It was then that early paleontologists began to piece together evidence from fossils, which revealed the record of a time when enormous reptiles had walked the earth. Not all of these dinosaurs were so large, however. Some were as small as chickens, while others—the sauropods, the largest terrestrial animals of all time—were the equivalent of half a dozen stories tall.

Some dinosaurs were awesomely fierce predators, while others were mild-mannered plant eaters. Dinosaurs fell into two groups based on the shape of their hips, which were either lizardlike or birdlike. Though the lizardlike Saurischia emerged first, they lived alongside the birdlike Ornithischia throughout the late Triassic, Jurassic, and Cretaceous periods. Ornithischia were all herbivores, or plant eaters, whereas Saurischia included both herbivores and carnivores, or meat eaters. Naturally, the most fierce of the dinosaurs were carnivores, a group that included the largest carnivore ever to walk the Earth, Tyrannosaurus rex.

Most dinosaurs had long tails and necks and walked on four legs, though some were bipedal, meaning either that they had only two legs or that they used only their two rear legs for movement or locomotion. Again, the shape of the creature correlated to some degree with its habits: all four-legged dinosaurs were relatively gentle, slow-moving herbivores, whereas most of the bipedal ones were fast-moving predators. Their teeth also reflected their diet: not surprisingly, carnivores had much sharper cutting surfaces shaped like serrated knives, which made it easy to rip their prey into smaller pieces before swallowing the pieces whole.

As recently as the 1970s, scientists tended to believe that dinosaurs were cold-blooded creatures markedly lacking in brain power. This view is reflected in a number of popular-culture sources, such as the 1983 song by the Police, "Walking in Your Footsteps," which suggests that if humans were to destroy themselves by nuclear warfare, they would seem even more "dumb" than the dinosaurs. By contrast, the film Jurassic Park, made a decade later, reflects changes in paleontologists' attitudes toward dinosaurs, gained as a result of continued research. As it turns out, dinosaurs were far from dumb, and they may even have been warm-blooded—unlike most reptiles but like birds, to whom they may have been related.

SOME TYPES OF DINOSAUR.

Few creatures have ever captured the imagination of humans as much as Tyrannosaurus rex —a particularly impressive feat, given the fact that the last T. rex died tens of millions of years before humans ever came on the scene. With a name that means "absolute ruler lizard" in Greek, this terrifying creature reached a maximum length of 45 ft. (14 m) and may have weighed as much as 9 tons (8 metric tons).

T. rex must have made a truly awesome sight running through the forests of its Mesozoic world. Moving on its powerful hind legs with a gait that was at once swift and lumbering, it used its tail as a counterbalance and stabilizer. Once it had come abreast of its prey, T. rex probably attacked its victim with powerful head butts and then tore the animal apart with its massive jaws before ripping into it with some 60 dagger-shaped teeth as much as 6 in. (15 cm) long.

Of course, T. rex is notable precisely because it was so unusual among dinosaurs in size and, for the most part, power. Deinonychus, for example, was much smaller—only about 10 ft. (3 m) and 220 lb. (100 kg)—but these "running lizards" were still fearsome predators, noted for their sickle-like claws. The phrase "sickle-like claws" might call to mind another creature, this one made famous by Jurassic Park: Velociraptor, or "swift plunderer," a walking death machine that for all the terror it inspired in moviegoers (and, no doubt, in many a Mesozoic creature) attained a length of only about 6 ft. (2 m).

Among the many lessons about dinosaurs to be learned from Jurassic Park was the striking contrast between herbivores and carnivores, a fact emphasized by the scene in which the two children take refuge with a herd of sauropods. These gentle giants possessed four legs the size of large pillars and had extraordinarily long necks and tails. Most famous among the sauropods was the Apatosaurus, which achieved a length of 65 ft. (20 m) and a weight of 30 tons (27 metric tons). Apatosaurus 's appearance in the scene with the children was not the great creature's first time in the limelight of popular culture: known as Brontosaurus until the early 1990s, this dinosaur was a popular fixture of the Flintstones cartoon.

In addition to land-based dinosaurs, there were such creatures as the flying Triceratops, which may have been a link between dinosaurs and birds. (The name raptor, incidentally, usually refers not to a type of dinosaur, but to a bird of prey.) It should be noted that Triceratops and Velociraptor were creatures of the late Cretaceous period, during which about a hundred different dinosaur genera (plural of genus ) flourished. This is an important point, because many books picture all manner of dinosaurs coexisting, when, in fact, various ones existed at different times over a period of about 180 million years. Also, it is worth noting that the major nonhuman "star" of Jurassic Park did not even live during the Jurassic period!

Later Mass Extinctions—and New Life

Today, of course, the dinosaurs are long gone—so distant in time, in fact, that the remains of many millions have become petroleum. This has happened in situations where specific conditions prevail: for example, the remains could not be allowed to rot, and decay had to be anaerobic and had to take place within certain types of rock. Yet oil reserves (for as long as they last) are not the only reason why the dinosaurs' disappearance was beneficial from the human standpoint. At the time when dinosaurs controlled the world, mammals were small and hid from predators such as T. rex. Without the mass extinction of the dinosaurs, this class of creatures might never have come to the forefront, and human beings might not have evolved.

Actually, two mass extinctions rocked the world of the dinosaurs. The first (fourth among the list of five major mass extinctions) happened at the end of the Triassic, the first period of the Mesozoic era. This was about 205 million years ago, when an asteroid may have hit Earth. Whatever the cause, the result was that creatures in the seas suffered major mass extinction. So, too, did those on the land, but many species of dinosaurs and mammals managed to survive the event, which marked the transition between the Triassic and Jurassic periods.

THEORIES REGARDING THE DINOSAURS' DEMISE.

The dinosaurs continued to flourish for another 140 million years, and their descendants might still be walking the earth were it not for the last great mass extinction, which took place about 65 million years ago. What killed the dinosaurs? Paleontologists and other scientists have proposed several theories: a rapid climate change; the emergence of new poisonous botanical species, eaten by herbivorous dinosaurs, that resulted in the passing of toxins along the food web; an inability to compete successfully with the rapidly evolving mammals; and even an epidemic disease to which the dinosaurs possessed no immunity.

Interesting as many of these theories are, none has gained anything like the widespread acceptance achieved by another scenario. According to this highly credible theory, an asteroid hit Earth, hurtling vast quantities of debris into the atmosphere, blocking out the sunlight, and greatly lowering Earth's surface temperature. Around the world, geologists have found traces of iridium deposited at a layer equivalent to the boundary between the Cretaceous and Tertiary periods, the Tertiary being the beginning of the present Cenozoic era. This is significant, because iridium seldom appears on Earth's surface—but it is found in asteroids.

THE ASTEROID HITS.

It appears that the asteroid smashed into what is now the northern tip of Mexico's Yucatán peninsula. Today that area is home to a crater some 6 mi. (9.6 km) deep and 186 mi. (300 km) in diameter. Note, however, that 65 million years ago, the Yucatán was not exactly where it is now. It had begun to drift in the direction of its present location, but the map of the future continent of North America was quite different from what it is today and included large submerged areas. Among them was the region of impact, which only later rose to the surface as a result of tectonic activity.

The nearest large landmass at the time was a good distance away—equivalent to northern Louisiana. But it hardly mattered that there were no dinosaurs at the point of impact. Traveling at more than 100,000 MPH (160,000 km/h), which is almost four times as fast as the fastest spacecraft built by human beings, the asteroid probably brought about an explosion as intense as many thousands of hydrogen bombs. It may not have raised a mushroom cloud per se, but it probably produced an even more dramatic formation as it sent more than 48,800 cu. mi. (200,000 km 3 ) of debris and gases into the atmosphere. This would be enough dust to cover the state of Mississippi to a depth of 1 mi. (1.6 km)

The sound of the impact must have been ear-shattering, even far away on what would one day become North America. Then came the tidal waves, some as tall as 394 ft. (120 m), with earthquakes soon to follow. But while these tidal waves undoubtedly caused massive localized death, or mass mortality, what really brought about the mass extinction of the dinosaurs was the aftermath of impact. All that dust in the atmosphere effectively blocked out the Sun's light, bringing about a dramatic cooling on Earth's surface. As a result, plants died, thus depriving herbivorous dinosaurs of an energy source. The herbivores died and then, in a domino effect brought about by the interdependence of components in the food web, the carnivores soon followed.

A STEROID APPROACHING EARTH. ACCORDING TO ONE THEORY, THE MASS EXTINCTION OF THE DINOSAURS RESULTED FROM THE IMPACT OF AN ASTEROID HITTING EARTH, HURTLING VAST QUANTITIES OF DEBRIS INTO THE ATMOSPHERE, BLOCKING OUT THE SUNLIGHT, AND GREATLY LOWERING EARTH'S SURFACE TEMPERATURE. (© D. Hardy. Photo Researchers. Reproduced by permission.)
A STEROID APPROACHING E ARTH . A CCORDING TO ONE THEORY , THE MASS EXTINCTION OF THE DINOSAURS RESULTED FROM THE IMPACT OF AN ASTEROID HITTING E ARTH , HURTLING VAST QUANTITIES OF DEBRIS INTO THE ATMOSPHERE , BLOCKING OUT THE SUNLIGHT , AND GREATLY LOWERING E ARTH ' S SURFACE TEMPERATURE . (
© D. Hardy. Photo Researchers
. Reproduced by permission. )

MAMMALS, HUMANS, AND MASS EXTINCTION.

When that asteroid hit, it brought an end to the dinosaurs and their Mesozoic world, ushering in the Cenozoic era, which saw the rise of mammals. Some examples of the creatures that proliferated in the course of the past 65 million years are tiny prehistoric horses with four toes as well as a giant rhinoceros-like herbivore, both of which lived in the Eocene epoch about 40 million years ago.

As time went on, the range of species—not only animals and plants but also the much less complex organisms of the other three kingdoms (Protista, including protozoa and algae; Monera such as bacteria; and Fungi)—grew larger and larger. An ice age struck the planet about 1.65 million years ago, bringing about much smaller cases of mass extinction than the ones we have discussed. But other instances of mass extinction would occur at the hands of a creature that appeared about 2.5 million years ago: Homo sapiens. The ice age—which was only one of many and thus is referred to often as the "last ice age"—would prove a major turning point in the history of the human species. At the beginning, we were just embarking on the beginnings of the Stone Age, whereas at the end, just 10,000 years ago (or a few seconds ago, in geologic terms), we emerged from the cold, ready to take over the world.

Near the end of the last ice age, peoples from Siberia crossed a land bridge spanning what is today the Bering Strait between Russia and Alaska. Their descendants, of course, are the Native Americans, and native is a fitting term, since they arrived in the Americas about 12,000 years ago, or about 7,000 years before the Europeans' ancestors arrived in Europe. What they found, as they poured into the Americas, was a range of species quite different from those known today. There were mammoth and mastodons; giant bears, beaver, and bison; and even saber-toothed "tigers" (which were not directly related to modern-day tigers), camels, and lions. Prehistoric America was also home to horses, but these creatures and many others were wiped out by hunting. Horses did not reappear in the New World until Europeans brought them after A.D. 1500, when they would prove an indispensable aid in European efforts to conquer the Native Americans' lands.

WHERE TO LEARN MORE

Cadbury, Deborah. Terrible Lizard: The First Dinosaur Hunters and the Birth of a New Science. New York: Holt, 2001.

Gould, Stephen Jay. Ever Since Darwin: Reflections in Natural History. New York: W. W. Norton, 1977.

K-12: Paleontology—Dinos (Web site). <http://www.ceismc.gatech.edu/busyt/paleo.html> .

Morris, S. Conway. The Crucible of Creation: The Burgess Shale and the Rise of Animals. New York: Oxford University Press, 1998.

Munro, Margaret, and Karen Reczuch. The Story of Life on Earth. Toronto: Douglas and McIntyre, 2000.

Oceans of Kansas Paleontology (Web site). <http://www.oceansofkansas.com/> .

Paleontology and Fossils Resources. University of Arizona Library, Tucson (Web site). <http://www.library.arizona.edu/users/mount/paleont.html> .

Palmer, Douglas. Atlas of the Prehistoric World. Bethesda, MD: Discovery Communications, 1999.

Raup, David M. Extinction: Bad Genes or Bad Luck? New York: W. W. Norton, 1991.

Singer, Ronald. Encyclopedia of Paleontology. Chicago: Fitzroy Dearborn Publishers, 1999.

Starr, Cecie, and Ralph Taggart. Biology: The Unity and Diversity of Life. 7th ed. Belmont, CA: Wadsworth, 1995.

University of California, Berkeley Museum of Paleontology (Web site). <http://www.ucmp.berkeley.edu/> .

USGS (United States Geological Survey) Paleontology Home Page (Web site). <http://geology.er.usgs.gov/paleo/> .



Also read article about Paleontology from Wikipedia

User Contributions:

Comment about this article, ask questions, or add new information about this topic: