Introduction The House of Millions of Years ''Let no one say the past is dead. The past is all about us and within'' --Oodgeroo Noonuccal, The Past ''What tempest blows me into that deep ocean of ages past, I do not know'' --Ole Worm I am looking out of the window, across farmland, houses, and parks, towards a place that for hundreds of years has been known as World''s End. It has this name because of its past remoteness from London, a city that has now grown to absorb it. But not too long ago this really was the end of the world. The soil here was laid down in the last ice age, a gravelly mixture deposited by rivers that once flowed into the Thames. As the glaciers advanced, they diverted its course, and the Thames now enters the sea more than 100 miles south of where it used to flow. From the ridged hills, clay crumpled by the weight of ice, it is possible, just about, to mentally strip away the hedgerows, the gardens, the streetlamps, and imagine another land, a cold world on the edge of an ice sheet extending hundreds of miles away. Below the icy gravel lies the London Clay, in which even older residents of this land are preserved - crocodiles, sea turtles, and early relatives of horses.

The landscape in which they lived was filled with forests of mangrove palm and pawpaw, and waters rich in seagrass and giant lily pads, a warm, tropical paradise. The worlds of the past can sometimes seem unimaginably distant. The geological history of the Earth stretches back about 4.5 billion years. Life has existed on this planet for about four billion years, and life larger than single-celled organisms for perhaps two billion years. The landscapes that have existed over geological time, revealed by the palaeontological record, are varied and, at times, quite other to the world of today. The Scottish geologist and writer Hugh Miller, musing on the length of geological time, said that all the years of human history ''do not extend into the yesterday of the globe, far less touch the myriads of ages spread out beyond''. That yesterday is certainly long.

If all 4.5 billion years of Earth''s history were to be condensed into a single day and played out, more than three million years of footage would go by every second. We would see ecosystems rapidly rise and fall as the species that constitute their living parts appear and become extinct. We would see continents drift, climatic conditions change in a blink, and sudden, dramatic events overturn long-lived communities with devastating consequences. The mass extinction event that extinguished pterosaurs, plesiosaurs and all non-bird dinosaurs would occur 21 seconds before the end. Written human history would begin in the last two thousandths of a second. At the beginning of the last thousandth of a second of that condensed past, a mortuary temple complex was built in Egypt, near the modern-day city of Luxor, the burial place of the pharaoh Ramesses II. Looking back to the building of the Ramesseum is a mere glance over the dizzying precipice of deep geological time, and yet that building is well known as a proverbial reminder of impermanence.

The Ramesseum is the site that inspired Percy Bysshe Shelley''s poem ''Ozymandias'', which contrasts the bombastic words of an all-powerful pharaoh with a landscape of what was, when the poem was written, nothing but sand. When I first read that poem, I had no knowledge of what it was about, and mistakenly assumed Ozymandias to be the name of some dinosaur. The name was long and unusual, and it was hard to figure out a pronunciation. The descriptive language used in the poem was that of tyranny and power, of stone, and of kings. The pattern, in short, fitted that of my childhood illustrated books about prehistoric life. At ''I met a traveller from an antique land who said: two vast and trunkless legs of stone stand in the desert '' , I thought of a plaster jacket being applied to the remains of some terrible beast from prehistory. A true tyrant lizard king, perhaps, now broken into bones and fragments of bones in the badlands of North America. Not all that is broken is lost.

The lines ''on the pedestal these words appear: "My name is Ozymandias, king of kings; Look on my works, ye Mighty, and despair!" Nothing beside remains.'' might be seen as time having the last laugh over a self-important ruler, but the world of that pharaoh has been remembered. The statue is evidence of its existence; the content of the words, the details of its style, clues to its context. Read like this, ''Ozymandias'' gives us a way to think about fossilized organisms and the environments in which they lived. Take out the hubris, and the poem can be read as being about finding the reality of the past from the remnants that survive to the present. Even a fragment can tell a story in itself, a piece of evidence for something beyond the lone and level sands, for something else that used to be here. For a world that no longer exists but is still discernible, hinted at by what lies among the rocks. The Ramesseum itself was originally known by a name that translates as ''The House of Millions of Years'', an epithet that could easily be appropriated for the Earth.

Our planet''s past also lies hidden under the dirt. It wears the scars of its formation and change in its crust, and it, too, is a mortuary, memorializing its inhabitants in stone, fossils acting as grave marker, mask and body. Those worlds, those otherlands, cannot be visited--at least, not in a physical sense. You can never visit the environments through which titanic dinosaurs strode, never walk on their soil nor swim in their water. The only way to experience them is rockwise, to read the imprints in the frozen sand and to imagine a disappeared Earth. This book is an exploration of the Earth as it used to exist, the changes that have occurred during its history, and the ways that life has found to adapt, or not. In each chapter, guided by the fossil record, we will visit a site from the geological past to observe the plants and animals, immerse ourselves in the landscape, and learn what we can about our own world from these extinct ecosystems. By visiting extinct sites with the mindset of a traveller, a safari-goer, I hope to bridge the distance from the past to the present.

When a landscape is made visible, made present, it is easier to get a sense of the often-familiar ways that organisms live, compete, mate, eat and die there.