There is no doubt that the human species has created a new, geologically significant epoch, the Anthropocene. About 12’000 years ago we entered the Holocene, which is characterised by the widespread appearance of homo sapiens. But only since the beginning of the industrial revolution mankind makes an impact on nature that is quite distinctive from any animalistic species that experiences explosive growth and dispersion across the globe. Explosive growth and dispersion of a species, followed by eventual collapse, is a well-known phenomenon in paleo-biology. Some events of this kind leave a geologically distinctive marker in the sedimentary record, sometimes in widely different settings between land and sea floor. Such marker horizons are the key to correlating sedimentary deposits of same age. It is one of the key tools for relative age dating in geology.
The traces of our existence, that an intelligent species may recognise in the distant future, will not be primarily ruins of cities, roads and waste dumps. This is a romantic view about a cyborg Indiana Jones. The main geological markers will be omnipresent traces of complex synthetic and toxic compounds in land sediments, in seabed sediments and in the water.
A clearly visible impact of the human species is the global change of the vegetation pattern. The changes from wooded plains to pastures by deforestation, or of arid lands to pastures and food-bearing farmland by irrigation bear witness to man’s cultivation of the countryside. Agriculture creates a significant change in continental erosion as well as continental and marine sedimentation. Whether it will be preserved depends on subsequent climatic and geological events. In seabed sediments the impact may be better preserved. Higher than natural concentrations of organic matter and nutrients are transported by fluvial discharge into the sea, where they are deposited, again marked by the presence of synthetic compounds. A sudden drop in biodiversity will be another significant marker.
With the use of fossil fuel to drive engines, mankind has set a completely new mark. Coal mining leaves its mark in the form of mine dumps or open pits. Large-scale ore mining, an epiphenomenon of industrialisation, leaves similar marks. Oil production will leave local traces of oil spills. Otherwise oil and gas production leave no significant evidence at the surface. The common signal is not at surface, but in the ground and in the atmosphere. All of the surface scars are local. As a meaningful marker they are not that significant, ugly and embarrassing though they may be. CO2 is the principal waste product of fossil fuels, but it may also not play a major role as a marker. CO2-emissions leave a discernible signal of increased concentration, it is however questionable whether this will leave a lasting impact in the sedimentary record. Its existence may be noticed indirectly on account of an increased vegetation cover. A far better marker will be fallout of soot and other air pollutants. Soot is a known marker for identifying past catastrophic wild fires. Soot from coal and oil combustion is easily distinguishable from that produced by wood burning. Sulphur oxides are known aerosols from volcanic eruptions, but the use of coal has contributed a continuous output of sulphur compounds into the air. This fallout will be recorded in the soils. But the prominent and unmistakable marker without precedent will be the presence of synthetic materials. Many of these products do not decay and may contain rare and toxic elements, which would never enter naturally into a sedimentary cycle in such compositions and concentrations.
Increasing global surface temperatures and raising sea levels may be recognised as an anthropogenic signal. It requires a discernible acceleration of temperature increase compared to the natural trend that is observed since pre-industrial times. Varying sea levels are a common phenomenon in the geological record. Sea level changes leave well-known patterns in the sedimentary sequence of continental shelves. In the last decades of the 20th century there was a common trend of anthropogenic CO2-emissions, of CO2-concentration in the atmosphere, of global surface temperatures and of mean sea level variations. They are all on the rise. The anthropogenic CO2-emissions have some influence on global CO2-concentration, but CO2 concentration and global surface temperatures onboth sea and land are mutually intertwined. Sea levels are dependent on surface and sea temperatures. At annual and even at decadal scale however, they show poor correlation. In the geological record the complex and chaotic interdependence of these systems may overprint the anthropogenic signal.
In order to leave a tidy planet for our descendants it may be advisable not to concentrate too much on one single parameter, like a quite innocent gas, but rather to concentrate on an efficient use of resources. This can be achieved by a dedicated recycling of limited resources. Turning our waste into resources is a formidable goal. The latest developments in nuclear engineering research, whereby radioactive used fuel becomes a fuel resource instead of a waste product, point exactly in the right direction. It is a promising option that we must support for the sake of our children.
The human species has left the animalistic path quite a while ago. I’m very optimistic that human ingenuity will master the challenge of limited resources. It may nevertheless not prevent the eventual collapse of the species. But let’s first welcome the Anthropocene.
