So what does the data of the Earth Time record consist of? Mostly, it is the flotsam and jetsam of all those earth processes that affect the surface of the Earth. These processes range from the familiar everyday work of wind and water to the more dramatic eruption of volcanoes, crumpling of rocks into mountains and the fortunately much rarer visitations by extraterrestrial impactors. The resulting flotsam and jetsam are predominantly rock and mineral debris, mostly in the form of mud and sand sediment, along with volcanic 'products' such as ash and lava.
Of great interest to us is the further additional data left by life and its past activities - in other words, fossils. Human activity has played an increasing impact on Earth's surface processes and deposits. While this human impact was initially recorded solely by the bones of our ancient relatives and their animal food, it quickly became more complex and diverse. From discarded tools and other cultural artefacts such as artworks, the human-generated 'fossil' record has grown to include the remains of settlement, technological development and modification of landscape.
So many lives of plants and animals over millions of years, so much activity, so many earth-shattering events, all reduced - 'earth to earth, ashes to ashes, dust to dust'. The 'sure and certain hope' here is that all this activity leaves some preservable debris. It does, but most of it is stored in the Earth's mineral and rock data bank along with some organic materials. Much of this data accumulates in layers piled successively through time one upon another. As we have noted, the oldest layer lies at the bottom of the pile and the youngest on top. However, just to complicate matters, there are also deeper-seated processes that can 'inject' other rock material data into the pile from below.
Most of what we think of as the diary of the Earth Time rock record is sequentially layered and any interpretation of the chronicle of the Earth has to be gleaned from this material rock and fossil record. Needless to say, it can be very difficult to read this diary and from it to reconstruct past environments, events, life and its development.
One of the keys to understanding the Earth Time chronicle is the appreciation that the layers are like the consecutive pages of a written narrative or diary, but with an important difference. First, the book has been vandalised, torn apart and scattered over the surface of the Earth. Bundles of unnumbered 'pages' lie here and there, but with many missing altogether. Secondly, many other pages are torn and damaged by being left to the destructive vagaries of the elements so as to be virtually indecipherable.
As a result, any attempt to follow the original narrative closely can be very difficult, as it has to be pieced together from the surviving pages. Another complication is that there are several different regional versions of the diary, as if they were in different languages, and in places the versions have become mixed up. Furthermore, to begin with none of the geologists who were trying to piece the diary together knew exactly how long each recorded chronological division was, but many of them thought they knew the overall duration of the chronicle, around 6000 years. The early 'brethren of the hammer', as they saw themselves, also thought they knew the outlines of Earth's story, because the Bible told them so. It was the Old Testament's Genesis narrative of creation followed by the Noachian Flood or Deluge and subsequent repopulation of the Earth by the descendants of Noah and the animals and plants he had saved from drowning in the ark.
Historians suffer from very similar problems with fragmentary, gappy data that can be difficult to read and interpret. Nevertheless, one of the great fascinations of geology and the 'testimony of the rocks' is that we have only scratched the surface of the Earth and the story of Earth Time. There is plenty of scope for new generations of enthusiasts really to make their mark on our understanding of the rock record. New finds, new techniques of investigation and even just taking a new critical look at received wisdom can produce startling results.
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