the question and answer list goes on and on.
This book attempts to answer these questions and more, taking you through the Triassic, Jurassic, and Cretaceous periods of geologic time when the dinosaurs roamed the earth. It tells you where scientists stand in terms of dinosaur discoveries, the newer species of dinosaurs, new possible reasons for the extinction of the animals, and especially why, as more dinosaur fossils are uncovered, the ideas about the evolution of dinosaurs will continue to change.
We invite you to enjoy reading about the most amazing creatures that ever walked, ran, hopped, loped, and stomped on the Earth. As the saying goes: “Dinosaurs Once Ruled!” If the current fascination with dinosaurs is any indication, they still do.
—Patricia Barnes-Svarney and Thomas E. Svarney
Acknowledgments
This book would not be possible without the hard work and dedication of the people at Visible Ink Press. Our thanks especially go to our editor, Kevin Hile, for his wonderful editing and insightful questions, and for making this dinosaur book so user-friendly! We also want to thank our agent, Agnes Birnbaum for all her help, patience, and friendship over the years.
—Patricia Barnes-Svarney and Thomas E. Svarney
IN THE BEGINNING
How old is Earth?
Earth is currently believed to be about 4.54 billion years old, but that number came after centuries of debate. In 1779, French naturalist Comte de Georges Louis Leclerc Buffon (1707–1788) caused a stir when he announced 75,000 years had gone by since Creation, the first time anyone had suggested that the planet was older than the biblical reference of 6,000 years. By 1830, Scottish geologist Charles Lyell (1797–1875) proposed that Earth must be several hundred million years old based on erosion rates; in 1844, British physicist William Thomson, later first baron of Largs (Lord) Kelvin, (1824–1907), determined that Earth was 100 million years old, based on his studies of the planet’s temperature. In 1907, American chemist and physicist Bertram Boltwood (1870–1927) used a radioactive dating technique to determine that a specific mineral was 4.1 billion years old (although later on, with a better knowledge of radioactivity, the mineral was found to be only 265 million years old). Using different adaptations of Boltwood’s methods on terrestrial, lunar, and meteorite (space rock that falls to the surface of Earth) material, scientists now estimate that Earth is between 4.54 and 4.567 billion years old.
How old is the oldest rock and mineral found on Earth?
The oldest rock discovered on Earth, the Acasta gneisses found in the tundra in northwestern Canada near the Great Slave Lake, is about 4.03 billion years old. The oldest minerals yet found are 4.404 billion years old and were found in Western Australia. The minerals—zircon crystals—eroded from their original rock, and then were deposited in younger rock.
Gases released by erupting volcanoes, such as carbon dioxide, nitrogen, and water vapor, did a great deal during Earth’s early history to make the atmosphere life-sustaining for plants and animals (iStock).
What caused the early Earth’s water and atmosphere to form?
No one really knows how the oceans filled with water. One theory is that volcanoes released enough water vapor to allow the oceans’ waters to condense. Another theory states that comets bombarded Earth just after the formation of the solar system, bringing enough water to eventually fill the oceans.
The origin of Earth’s atmosphere is also debated, but not as intensely. In this case, it is more likely that some of the atmosphere originated from gases that were part of the solar nebula, gases brought by comets, and those produced from volcanic activity. Earth probably would have had a thicker atmosphere, too, but the young, active Sun’s heat boiled away the lighter materials—elements that are still found today around the gas giant planets Jupiter, Saturn, Uranus, and Neptune.
What gases began to accumulate after Earth’s crust finally solidified?
As Earth’s crust solidified, gases began pouring out of fissures and volcanoes, accumulating in the forming atmosphere. These same gases still emanate from modern volcanoes, and include carbon dioxide (CO2), water vapor (H2O), carbon monoxide (CO), nitrogen (N2), and hydrogen chloride (HCl).
As these gases interacted in the atmosphere, they combined to form hydrogen cyanide (HCN), methane (CH4), ammonia (NH4), and many other compounds. This atmosphere would be lethal to most present day life-forms. Fortunately for life on Earth, over the next two to three billion years the atmosphere continued to change until it reached close to its present composition.
Lilies are grown in a greenhouse in Almere, the Netherlands. Just as this structure allows tropical plants to grow in a cold climate, the natural greenhouse effect created by Earth’s atmosphere warms our planet (iStock).
How did oxygen form on early Earth?
The early atmosphere was composed mainly of water vapor, carbon dioxide and monoxide, nitrogen, hydrogen, and other gases released by volcanoes. By about 4.3 billion years ago, the atmosphere contained no oxygen and about 54 percent carbon dioxide. About 2.2 billion years ago, plants in the oceans began to produce oxygen by photosynthesis, which involved taking in carbon dioxide. By two billion years ago, there was one percent oxygen in the atmosphere, and plants and carbonate rocks caused carbon dioxide levels to decline to only four percent. By about 600 million years ago, atmospheric oxygen continued to increase as volcanoes and climate changes buried a great deal of plant material—plants that would have absorbed oxygen from the atmosphere if they had decomposed in the open. Today, our planet’s atmosphere levels measure 21 percent oxygen, 78 percent nitrogen, and only 0.036 percent carbon dioxide.
What is the greenhouse effect?
The greenhouse effect, as its name implies, describes a warming phenomenon. In a greenhouse structure, closed glass windows cause heat to become trapped inside. The greenhouse effect functions in a similar manner, but on a planetary scale. In general, it occurs when the planet’s atmosphere allows heat from the Sun to enter but refuses to let it leave.
Without this greenhouse effect on Earth, life as we know it would not exist. On our planet, solar radiation passes through the atmosphere and strikes the surface. As it is reflected back toward space, some solar radiation is trapped by atmospheric gases such as carbon dioxide, methane, chlorofluorocarbons, and water vapor, resulting in the gradual increase of Earth’s temperatures. The rest of the radiation escapes back into space. Without this heat, life as we know it would be impossible, Earth would be about 100 degrees cooler, and the oceans would freeze.
Why is global warming important to humans?
The scientific consensus is that global average temperatures are rising, a phenomenon often referred to as global warming. Many scientists believe human activity has greatly contributed to the buildup of greenhouse gases in Earth’s atmosphere in the past century or so, and hence Earth’s gradual warming—around 1 degree Fahrenheit (0.5° Celsius). One recent study by an international panel of scientists predicted that the global average temperature could increase between 2.5 and 10.4° Fahrenheit (1.4 and 5.8° Celsius) by the year 2100 and that sea levels could rise by up to 2 feet (just over a half meter).
What is the biggest culprit? Although there are