Great Ideas of Science

How are polar bears related to pandas? For thousands of years, philosophers and scientists have tried to organize and understand, or classify, the relationships among Earth's animals and plants. Early classification systems were cumbersome and inconsistent. In the late 1720s, Carl Linnaeus began developing a classification system to describe relationships among all living things, including animals, plants, fungi, and bacteria. This organization, called the tree of life, is still the basis of the classification system used by scientists today. Recent scientific discoveries-such as the ability to decode DNA, the chemical code shared by all living things-have given biologists new insight into the tree of life. As new species are discovered and new information about old species is unearthed, the classification system continues to change. This book tells the story of how the science of classification has revolutionized the way we look at life on our planet.

Outraged people claimed that Darwin's theory had made humans the relatives of monkeys. Scientists were sure that species changed over time, but no one could explain how. In the 1800s, Charles Darwin's studies of thousands of specimens of living things showed that no two individuals of any species were exactly alike. He realized that over millions of years, some individuals had traits that gave them an edge to survive and reproduce. As they reproduced, the successful traits were inherited by later generations. This book explains Darwin's theory. It shows how later discoveries in genetics provided more evidence that the theory of evolution works. Each year, scientists in many fields are making new discoveries that provide further proof of Darwin's world-shaking ideas.

If a black dog and a white dog have puppies, what color will the puppies be? Genetic scientists have been trying to answer this question for hundreds of years. Genetics is the science of heredity-how traits are passed from parents to offspring. One of the first breakthroughs came from Gregor Mendel, a nineteenth-century monk who spent eight years breeding thousands of pea plants. Pea plants might seem pretty different from dogs, but on a microscopic level, they have a surprising amount in common. Genetic pioneers of the twentieth century unlocked the secrets of DNA, the molecule that holds heredity information for all life-forms. Thjis book tells the story of how scientists cracked the code of life and revolutionized molecular biology.

Since prehistoric times, people have wondered what causes disease. Early people blamed evil spirits. Later, disease was thought to be caused by an imbalance of bodily fluids. By trial and error, people discovered plants that cured certain ailments. But disease still spread through dirty, crowded cities. In 1546 an Italian physician proposed that tiny, invisible bodies cause disease. By the end of the nineteenth century, doctors had discovered the microscopic organisms we call bacteria and viruses. This breakthrough led to techniques we take for granted, such as vaccination, the pasteurization of dairy products, sterilization of medical instruments, and the use of anibiotics. This book tells the story of how scientists learned about germs and revolutionized medicine.

What are cells made of? Biologists have been studying cells since the mid-1600s, when Robert Hooke viewed a slice of cork through a microscope and coined the word "cell" to describe the walled-in spaces he saw. Most cells are invisible to the naked eye. Yet they carry out the many complex processes that make life possible. As microscopes have improved, scientists have learned more and more about cells and their organelles-the structures within cells. From the nucleus, the cell's control center, to the tiny ribosomes, which help manufacture proteins, each part of a cell plays an essential role. This book tells the story of how biologists unlocked the secrets of cells and revolutionized the way we look at living things.

For hundreds of years, people found the fossils of ancient sea creatures at the tops of tall mountains. Scientists puzzled over this problem. A fish couldn't have swum up a mountain. And how could rocks on a mountain move up from the bottom of a sea? Geologists finally found the answers they needed in the 1960s, when they developed the theory of plate tectonics. This theory revolutionized our understanding of the earth. Plate tectonics explains how volcanoes form, why earthquakes happen, and what goes on deep inside the earth to make the continents move. This book tells the story of scientists and their discoveries to explain how the theory of plate tectonics came to be.

Since prehistoric times, people have been fascinated by electricity and magnetism. Ancient people marveled at the auroras-streaks of colored light that appear in the night sky near the poles. They wondered about the ability of materials such as amber and magnetite rock to attract or repel other objects. Many people believed magic was behind these phenomena. Then, in the 1600s, scientists began to lift the fog of superstition. Electricity and magnetism are behind some of life's greatest mysteries-the auroras, the beating of the human heart, and even the twisting of time and space known as relativity. This book tells the story of scientists and their discoveries to explain how the theory of electromagnetism came to be.

Since prehistoric times, people have wondered how the universe works. Early scientists studied how forces affect objects and watched how heavenly bodies move. In 1687 Isaac Newton published a set of laws that described the motion of all objects, both on Earth and in the heavens. By 1900 many physicists believed only a few questions remained to be answered. But the early 1900s brought revolutionary developments in physics. One was Albert Einstein's theory of relativity. This theory proposed completely new ideas of time, space, mass, motion, and gravity. Einstein's theory revealed that matter and energy are interchangeable, rather than distinct. This book tells the story of how the theory of relativity revolutionized physics.

Where did our universe come from? People have been trying to answer this question for thousands of years. The twentieth century brough new discoveries in physics and astronomy that led scientists to develop the Big Bang theory-a detailed idea that describes how our universe formed. According to this theory, the entire universe began in a single instant, in an unimaginably powerful explosion. That explosion created all time and space, all matter and energy-everything in the universe as we know it. This book tells the story of how scientists' observations of the stars led to the development of the Big Bang Theory.

What is matter made of? Scientists have been trying to answer this question for thousands of years. The concept of the atom-the tiniest fragment of a substance that still retains the characteristics of that substance-goes back to the Greek philosopher Leucippus, who lived in about 450 b.c. In the mid-1600s, Robert Boyle provided experimental evidence that atoms did, indeed, exist. And in 1897, British physicist Joseph John Thomson discovered the first subatomic particle: the electron. Yet even the tiny components of the atom-protons, electrons, and neutrons-are not the smallest things in the universe. Subatomic particles are made up of still tinier objects called quarks and leptons. This book tells the story of how scientists unlocked the secrets of the atom and revolutionized the way we look at the world around us.