Humberside Geologist No. 13
Millenium, Time for reflection on Time and tides.
At a few minutes to midnight on 31st December 1999 I stood looking out to sea across the Solent, watching fireworks arc into the sky and waves beat an incessant rhythm on the beach at my feet. As the tide rose in its own slow rhythm I began to muse on our conception of time. Earlier I had watched, courtesy of the miracle of television, the dawn sweeping around the globe, a process with "no vestige of a beginning, no prospect of an end." It is only human convenience that a day ‘starts’ as the sun reaches a certain position relative to the international dateline and a year begins as the earth reaches a particular place in its orbit around the sun. The decimal system, so crucial to our placing a significance on dates that are convenient multiples of ten is linked to out possession (in most cases) of ten digits, a number that seems to grant no particular evolutionary advantage over eight or twelve. If the dice of DNA had rolled differently or if there had been an evolutionary advantage to a differing number of digits what would we have been celebrating and when? Even those seemingly fixed points, the day and the year are inconstant. The Moon, whose gravitational couple creates the tides also acts to slow the Earth’s rotation. Growth rings on corals of Devonian age indicate that a year consisted of approximately 400 days at that time, a figure that confirms the theoretical predictions of astrophysics.
As I mused I stood on a modern beach overlying sediments of Eocene age. These rocks, the Bracklesham Group represent a series of transgressions and regressions, a great ebb and flow of sea level rise and fall over approximately ten million years. (1) Gazing out to sea the fireworks were reflected in water that had inundated what to our paleolithic ancestors would have been just low-lying land and rivers before the waters rose and the climate warmed at the end of the Devensian glacial episode, sweeping higher than the current sea level and leaving behind a raised beach. Later, Mediaeval settlers would build a village at Bracklesham only for it to be destroyed by coastal erosion.
Across the water the bulk of the Isle of Wight loomed, illuminated by the occasional flare of light, its chalk of Cretaceous age, a time when the tides swept over much of Europe, drowning much of it for millions of years in its clear tropical waters. When these great waters withdrew the great race of ammonites was no more and dinosaurs, dominant on the land for 150 million years had disappeared to be replaced by small snuffling creatures that suckled their young and whose progeny would eventually include you and me.
For the complex, symbol using primate that is mankind the dawn of the year 2000 A.D. has great significance as our need for ritual and celebration at this time demonstrates. For geologists it is perhaps humbling that this immense span of time in human history is a mere 0.000 04% of the history of the Earth we study.
1: The Bracklesham group show evidence of three major transgressive cycles, part of eleven major sedimentary cycles in the Hampshire Basin. (Cordiner 1982) The facies are marine Û estuarine/coastal swamp. (Bone & Bone 1985, Kemp, Kemp & Ward 1990)
Bone, Anne & Bone, David (1985) Fossils from Bracklesham to Selsey Chichester District Museum, Chichester.
Cordiner, Roger. (1982) Sedimentary Cycles in the Tertiary Strata in South East England West Sussex Geological Journal West Sussex Geological Society. Worthing.
Kemp, David. Kemp, Liz. & Ward, David. (1990) An illustrated guide to the British Middle Eocene vertebrates David Ward. London