The early history of our planet covers such vast stretches of time that years, centuries, and even millennia become virtually meaningless. Instead, paleontologists and scientists who study geochronology divide time into periods and eras.

The current view of science is that planet Earth is around 4.6 billion years old. The first four billion years of its development are known as the Precambrian period. For the first billion years or so, there was no life in Earth. Then, the first single-celled life-forms, early bacteria and algae, began to emerge. We don’t know where they came from or even if they originated on this planet, at all.

This gradual development continued until around four billion years ago, when suddenly (in geological terms) more complex forms of life began to emerge. Scientists call this time of an explosion of new forms of life the Paleozoic Era, and it stretched from around 541 to 250 million years ago (Mya). First of all, in the oceans and then on land, new creatures and plants began to appear in bewildering variety. By the end of this period, life on Earth had exploded into a myriad of complex forms that filled virtually every habitat and niche available in the seas and on the planet’s only continent Pangea.

Then, a mysterious event that became known to early paleontologists as “The Great Dying” wiped out more than 95 percent of all life on Earth. No one is entirely certain what caused this, but the effect of this cataclysm was as if someone had pressed a great cosmic “reset” button and it took 30 million years for the development of life on Earth to start again.

The next period of Earth’s history is known as the Mesozoic Era, from about 252 to 66 Mya. This era is further divided into three periods - the Triassic, Jurassic and Cretaceous. During this era, one type of life came to dominate the planet more completely and for a longer period than had been seen before or since; this was the Age of Reptiles.

Beginning in the Triassic, but especially in the Jurassic period, reptiles came to dominate the oceans, land and even the skies. There has never been anything else quite like this period in terms of the success of a particular type of creature. For almost 200 million years, reptiles were the only significant creatures on Earth. They were so successful and so diverse that they evolved to take advantage of every available habitat and no other type of large creature had a chance to develop.

To put the 200 million years of reptile dominance in perspective, the entire span of recorded human history - the time since people advanced from tribes of primitive, nomadic hunter-gatherers into recognizable societies - covers less than 6,000 years. To put this in context, if the entire history of the planet were to be laid out on the length of a football field, the period of dominance of the age of reptiles would not begin until the five-yard line and would stretch for twelve feet. All of human history would occupy a tiny strip at the end of the field, less than the width of a human hair.

It was during the Jurassic period that reptiles began rule the Earth and some of the best-known prehistoric creatures first emerged. The Jurassic Period: The History and Legacy of the Geologic Era Most Associated with Dinosaurs looks at the development of the era, the extinction events that preceded it, and how life began to evolve during it. You will learn about the Jurassic Period like never before.