Geoscience Reference
In-Depth Information
the Roman Empire was in full swing. And 150 generations back, the Great Pyramid of An-
cient Egypt had not been constructed. About 300 generations takes us back to the Neolith-
ic 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 mito-
chondrial 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.
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.
Now think again of the changes that can take place in a few generations. 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'.
Flood and uniformity
Humans have noticed fossil remains since prehistoric times. There are ancient stone tools
that appear to have been chipped so as to show off a fossil shell. The fossilized stem of a
giant cycad was placed in an ancient Etruscan burial chamber. But attempts to understand
the nature of fossils are comparatively recent. The science of geology arose primarily in
Christian Europe where beliefs based on biblical stories made it unsurprising to discover
the shells and bones of extinct creatures high up in mountainous regions: they were the
remains of animals that perished in the biblical flood. Even granite, it was suggested by so-