The Anthropocene: What's in a name? The Human Impact on Our Planet

The Earth has been around for a long time. Of the 4.54 billion years our planet has been around, these can be split down into geological time periods; a chronological measurement that describes the relationships of different events that have happened throughout the Earth’s history.

Geological time scale. Eons down the centre, periods on the right. Block size does not represent length of time.

There is a very interesting analogy that compares geological time periods to a 24 hour clock to put into perspective the length of different events, the following text from Northern Arizona University surmises this quite nicely:

“The Earth forms at 12:00 am, and cools down from a molten state over the next several hours. The oceans form and the asteroid bombardment diminishes. Very primitive single celled life appears very quickly, before 4:00 am, and photosynthetic organisms appear before 6:00 am. Right around noon, the atmosphere becomes oxygen rich. By 1:00 pm (13:00 h) the single-celled eukaryotes have arrived. By 5:00 pm (17:00 h) the first multicellular forms appear. The first aquatic animals don't arrive until after 8:00 pm. Plants colonize land at 9:30 pm and land animals follow at 10:00 pm. The dinosaurs are the life of the party for about an hour; from 10:40 pm to 11:40 pm. Human ancestors split off from the rest of the hominids at only two minutes to midnight, and modern humans arrive as the clock strikes midnight.”

The term Anthropocene: Origins

Humans are having such a big impact on our planet, that the term ‘Anthropocene’ (anthropogenic: originating in human activity) was coined in the 1980s and then popularised by Paul Crutzen and Eugene Stoermer in 2000 as in informal term to describe the current time we are living in. Once formalised, the Anthropocene will the a geological epoch, which is a unit that fits into the geological period mentioned above in the same way that a millimetre is a sub-unit of a centimetre.

To formally recognise this new geological epoch, geologists have to see concrete proof that humans are having an impact on the rock record itself. This means having a lasting and meaningful impact on the chemical composition of rocks and fossils, which may not be visible for millions of years. Geologists are looking for what is known as the ‘golden spike’ ; this is a marker in the fossil record that would provide definitive proof that could separate the Holocene, the epoch that has lasted for 11,650 years, from the proposed Anthropocene. This would have to be something significant so that it was still distinguishable millions of years into the future.

Finding the 'golden spike'

Baker nuclear explosions 25 July 1946

One contender involves the world’s loneliest tree, the Sitka spruce which is the only tree on Campbell Island, a remote island off the coast of New Zealand. Delving a little deeper into the story, the 1960s were the peak of nuclear testing. Spikes of radioactivity have been found in lake sediments and the annual growth rings of trees, however these were mainly found in the northern hemisphere where the testing took place. A recent study published in the journal Scientific Reports shows that a spike of radioactivity was found in the Sitka spruce on the aforementioned island, peaking October-December 1965. This matches other records in the northern hemisphere, making the record global.

Location of the Sitka Spruce tree. Image credit: BBC News.

Microplastics on the ocean floor are another piece of evidence that could be counted towards the current time being termed the Anthropocene. A recent article by BBC news showed that a study lead by the University of Manchester had found up to 1.9 million plastic pieces per square metre, with powerful bottom currents in the ocean playing a part in accumulating areas of high microplastic concentration. Out of the 4 to 12 million tonnes of plastic that enters the ocean each year, only 1% of it is the plastic that we think of floating as visible trash, or washing up on coastlines. There is nothing unusual about the study area for this research between Italy, Corsica, and Sardinia, so if other large quantities of microplastics such as this are found across the globe, this may help to further define the Anthropocene. This is because over time, these plastics along with the sediment they lie alongside will undergo the process of lithification to form rocks; with the plastics entering the rock record in such a way, this provides unequivocal evidence of humans altering the rock record, which may be preserved for millennia.

Others use the start of the British Industrial Revolution which created the world’s first fossil fuel economy and started the anthropogenic increase of greenhouse gases in the atmosphere, or even earlier when humans started farming. This is a topic that is still up for debate, and still requires more research to pinpoint the ‘golden spike’, however it is without a doubt that we are living in a time where humans have become the most influential species on the planet, affecting land, water, the atmosphere, and other organisms. 

Useful links:

https://www.nhm.ac.uk/discover/what-is-the-anthropocene.html