17 May 2011

The Anthropocene: really an epoch?

That a planet can conserve traces of long extinct life is clear from the presence of fossils on the Earth. Many have searched for evidence of some kind of fossil also on Mars, and in the future we hope to detect traces of life from the chemical signatures in the atmospheres of extrasolar planets. Certain of the fact that life, especially "intelligent" life, is able to alter its host environment, various researchers are trying to decide whether the presence of Man on Earth has already had an impact sufficient to define a new geological epoch. In other words, whether our activity on the Earth is sufficient to influence future epochs.
All this was discussed last week in London at a symposium of the British Geological Society. Many scientists from various fields were present, among them Paul Crutzen, winner of the Nobel prize for his part in identifying the man-made agents responsible for ozone depletion. Crutzen also coined the phrase "Anthropocene", used ever more frequently to describe the present planet-scale changes that many believe to be due to Man's activities, although there is still no agreement as to when this period began, and certainly not as to when it might end.
Officially we are presently in the Holocene epoch, that began at the end of the last ice age 12,000 years ago. One of the strongest pieces of evidence for the definition of a new epoch are the levels of atmospheric CO₂, that for the last 12,000 years have been stable at between 260 and 285 parts per million (ppm), whereas today's value is 390 ppm. At least part of this rise can be attributed to the burning of fossil fuels.
This might not be sufficient to add the Anthropocene to the list of roughly 150 eons, periods, epochs and ages into which the Earth's history over the last 3.6 billion years has been divided, but there are also other factors to take into account. For example, the decades of mining to extract primary materials from the crust, and the large scale hydro-electric projects (such as the dam on the Yangtze river in China, shown above from space, that has modified the local climate).
Adding to these, things like deforestation and the reduction of biodiversity favoured (involuntarily) by intercontinental transport and it becomes more likely that the changes on the Earth system will leave traces that will be detectable even in the very distant future. The indelible signature left by our inability to live in harmony with nature.