1. The world is not only large in its spatial dimensions. It also extends almost unimaginably far back in time.
It is impossible to get a full grasp of the concepts and processes at work in geology without an understanding of what writers John McPhee, Stephen Jay Gould, and Henry Gee have referred to as ‘deep time’.
2. Most of us know our parents, many remember our grandparents. Only a few have met great grandparents.
Their youth lies more than a century in our past, a time which seems alien to us with our vastly different scientific understanding and social structure. Just a dozen generations back, England was ruled by Queen Elizabeth 1, motorized transport and electronic communication was undreamt of, and Europeans were exploring the Americas for the first time. Fifty generations ago, the Roman Empire was in full swing. And 150 generations back, the Great Pyramid of Ancient Egypt had not been constructed. About 300
generations takes us back to the Neolithic in Europe at a time when the last Ice Age had only just ended and simple agriculture was the latest technological revolution. It is unlikely that archaeology can reveal where our ancestors were living at that time, though comparisons of our maternally inherited mitochondrial DNA may indicate the broad region. Add another zero to the year and we have gone back
3,000 generations to 100,000 years ago. At this time, we cannot trace separate ancestry of any living racial group. Mitochondrial DNA suggests that there was a single maternal ancestor of all modern humans in Africa not long before. But, in geological time, this is still recent.
3. Ten times older at a million years and we start to lose track of the modern human species. Another factor of ten and we are looking at the fossil remains of early ape ancestors. This far back it’s impossible to point even to a single species and say with certainty that amongst these individuals was our ancestor.
Multiply by ten again and, 100 million years ago, we are in the age of the dinosaurs. The ancestor of
humans must be some insignificant shrew-like creature. A thousand million years ago and we are back amongst the first fossils, maybe before even the first recognizable animals. Ten billion years ago and we are before the birth of the Sun and solar system, at a time when the atoms that today make up our planet and ourselves were being cooked in the nuclear furnaces of other stars. Time is indeed deep.
4. Historical time is trivial compared to the age of the Earth, yet a few centuries have seen many volcanic eruptions, cataclysmic earthquakes, and devastating landslides. And think of the relentless progress of less devastating changes. In 30 generations, parts of the Himalayas have risen by maybe a metre or more.
But at the same time they have eroded, probably by more than this. Islands have been born, others washed away. Some coasts have eroded back hundreds of metres, others have been left high and dry. The Atlantic has widened by about 30 metres. Now multiply all these comparatively recent changes by factors of ten or a hundred or a thousand, and you are beginning to see what can happen over geological ‘deep time’.