Earth Time trends and events

For historians, recent political, economic and cultural trends are of importance, especially global economic trends and events such as stock market crashes. And as we know, such crashes are sometimes the result of specific events such as the September nth, 2001 attack on the World Trade Center in New York. As we shall see, such catastrophic events have parallels in geological history. However, very few of these historical events are likely to leave any trace in the future geological record, only those that leave widespread evidence of collateral damage.

Even evidence (of a purely geological nature) for a large-scale conflict such as the 1914-18 First World War will be hard to come by outside of the battlefields. In regions like Flanders on the French-Belgian border, where there was intense and prolonged fighting, there will be some 'debitage' remaining. Bones and even metal degrade on the geological scale, although concrete as used in the building of the Maginot defence line is more persistent. Military hardware or ships that end up on the seabed also persist quite well but can be difficult to find. The event associated with the 1939-45 Second World War that is most likely to be picked up is the dropping of the atomic bombs on Japan. Radioactive particles (isotopes of caesium and plutonium) from the nuclear test explosions carried out by the American military in the Nevada desert in the 1950s were carried through the atmosphere and around the world by the jet stream within days. Recently they have been recovered from soil samples taken at the time in Hertfordshire, England. Although present in extremely minute traces that do not endanger life, they still reside in measurable quantities even 50 years after being released into the atmosphere. Similar man-made potentially dangerous pollutants can be found in ice cores from Greenland and Antarctica.

Archaeologists of the future may be able to recover evidence of some economic developments and trends, especially from their favoured haunt - the rubbish dump. Our huge landfill dumps will provide rich pickings in the future. Resistant and preservable items such as glass bottles will be one of the mainstays, with chronologies based on the evolution of shape, design of the stopper and chemistry of the glass. No doubt the ubiquitous and globally distributed cola bottle will provide an excellent international standard for the chronology of the twentieth century. However, the large-scale replacement of the bottle by the metal can will severely limit the usefulness of the bottle timescale into the twenty-first century.

Nevertheless, most of the archaeological record will be swept away over geological time. Very little of the archaeology of human prehistory and history will remain except for eroded stone tools and rock-derived material used for building. Much of the Earth's landsurfaces will eventually be inundated by future seas. And, as the waters transgress across any low-lying areas, they will destroy all but the most resistant structures. Wave action and marine currents will redistribute and deposit the bits as new sediment on the seafloor, where they will stand a better chance of being preserved as future marine strata, but very little of the original terrestrial structures or materials will be recognisable. Much of the record of the long-extinct, land-living dinosaurs is preserved in this way. The sheer size and toughness of their bones have allowed them to persist through destructive processes of decay, erosion, transport and redeposition offshore from the lands they originally occupied.

However, there are a number of other important processes and events that are currently recording the passage of time in newly formed rocks and sediments. These range from chemical traces and signatures to changes in the Earth's magnetic field. Some of the former can record climate change, industrial activity and largescale volcanic activity as well as the explosion of nuclear devices.

No doubt with our hominocentric view of the world we expect that the future rock record will be replete with evidence of our human triumphs and disasters. But this is not necessarily so, and it is worth considering just what the rock record typically consists of. All the average human can expect is that, if buried, our remains might be preserved in the short term. However, on the longer geological timescale our remains, like most deposits on land, will be eroded away. As more and more people are cremated, it is probably best to be 'green' about your futurity and hope that gases derived from incineration will be recycled through the atmosphere into some plant and not contribute too much to global warming.

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