As you read this book you will find that the history of life and the his-
tory of the rocks are deeply and intricately connected.The rocks contain frag-
ments and records of former living things, allowing us to reconstruct the story
of their development. But those creatures have also had great impacts on sed-
iments, the oceans, and the atmosphere of the planet. It was those first prim-
itive photosynthetic organisms, for example, that began to pump oxygen into
the early atmosphere. To them it was a waste product of energy capture, but
its production so altered the history of the Earth that both the rocks and the
subsequent forms of life were profoundly influenced by its presence. The
development of photosynthesis can thus be regarded as the single most impor-
tant step in the evolution of life. It was the turning point that was to paint the
planet green. With oxygen in the atmosphere, conditions became right for
massive chemical changes, such as the rusting of iron, and, more important, the
scene was set for living things to invade the land.
The sheer diversity of forms that life has adopted defies the imagination.
We still delight in the Earth’s biodiversity, but what remains is only a tiny frac-
tion of what lies dead and preserved beneath our feet in the rocks.The fossils
of lost life-forms imply great rates of extinction, sometimes resulting from cat-
astrophes of mind-bending magnitude, such as the asteroid collision with the
Earth at the time of the demise of the dinosaurs. The recurrent spread of ice
sheets at times in the Earth’s history have also left their mark on the rocks and
on current patterns of life, as have the lumbering movements of whole con-
tinents, tearing apart, drifting, and colliding over the crust of the planet.
In the final scene of the story set out in this book there arrives a new
player—our own species. No other biological event since the development of
photosynthesis has had such a major impact on the planet. The current rates
of extinction may prove as disastrous for the Earth as the arrival of another
asteroid. We can only hope that the appreciation of our biological and geo-
logical heritage,as set out here, will help to make the reader aware of the dan-
gers and thus reduce the effects of our impact on this planet. Perhaps the last
chapter of this book will not prove to be the final chapter after all.—Peter D. Moore, Ph.D.X
Historical Geology