Climate Change and in general environmental problems are omnipresent topics these days. By now, the Earth has changed so much by humans activities that we have even entered a new geological epoch – the Anthropocene.
Before it came that far, many things happened on Earth since it was formed ~4.5 billion years ago. In the first 560 million years, a time called the Hadean, a lot of bombardments still hit the Earth and no rocks are preserved from this time except some 4.2 billion years old minerals called zircons. The oldest real rocks found on Earth have formed 4 billion years ago when the Archean began. Around 3.8 billion years ago, the temperatures were finally low enough for the oceans to fill with water. In this Archean ocean, first organic compounds and then life originated. There are many theories about how exactely it happened and most likely we will never find out. Also, when exactely it happened is unclear, probably around 3.7 billion years ago as some preserved rocks indicate. First signs of oxygen producing organisms were found in 3.5 billion year old rocks. The single cell life developed and 2.5 billion years ago, in the Proterozoic, phototrophic microorganisms could produce so much oxygen, it accumulated in the atmosphere. After that, eukaryotic life with a cell nucleus could evolve. Around this time, the ‘boring billion’ started, a term used for a time of Earth, were conditions were relatively stable and no multicellular life had developed yet. Afterwards, life developed in the oceans and many, many different animal species evolved. The land was conquered later by life, 500 million years ago in the Phanerozoic, first by animals, then by land plants. Human-like ancestors of us on two feet, the hominins, just developed ~2 million years ago and homo sapiens around 300,000 years ago. This and many more thing happened in the History of Earth and humans just exist since a breath of air compared to the age of the Earth.
The geological time scale is divided into eons, eras, and periods, epochs, and ages to divide the history of Earth into segments of time. The change from one time to another needs to be defined by something that is now recorded in the rocks. This could be a change in rock’s characteristics or a change in fossils. With the findings of fossils, five mass extinctions could be detected within the last 550 Ma. Apart from the spectacular mass extinction of the dinosaurs, there were four others, caused e.g. by the ocean that turned anoxic, probably due to underwater volcanoes, or by a changing pH in the ocean, so many species just dissolved. The exact time points that define the geological time scale are mostly stated with uncertainties as techniques to date rocks are getting less precise as older the rock gets. The International Commission of Stratigraphy is continually evaluating the available knowledge and the newest findings and updating the official stratigraphy of Earth.
The Earth is constantly changing since it was formed. Most of the changes are from our perspective very, very slow processes like the evolution of life. Of course, there were also relatively fast natural events like massive volcano eruptions or meteor impacts that caused major changes on Earth. But in the last decades and centuries, the Earth has changed much faster than usual – just because of human activities. And all of the Earth’s spheres are affected by humans. Currently, even a sixth mass extinction is proceeding as a majority of wild animal individuals have disappeared and species continue to die out. Because of all anthropogenic impacts, humans started to take a special place in the history of Earth – ‘special’ not in a good sense.
Some smart people started in the 1930s to think about giving the current time a new name for the time of humans but finally, the term of the Anthropocene got popular by Nobel prize-winning chemist Paul Crutzen. He introduced it to the scientific community and published the article ‘Geology of mankind’ in the journal Nature in 2002. The most severe changes of the Earth that he mentioned were methane and carbon dioxide emissions, deforestation of the tropical rainforests, the use of fresh water, overfishing, the release of toxic substances, the destruction of the ozone layer, and climate change. As start of this new epoch of the humans, he proposed the late 18th century, when atmospheric concentrations of carbon dioxide and methane started to rise, which have been detected by measuring air that was trapped in ice.
With Crutzen’s proposal a controversial discussion about officializing the Anthropocene started that is still ongoing. Some people did not agree at all with the idea of the Anthropocene but these voices got less and less. Another big question among the scientists is, at what time they should fix the start of the Anthropocene. Strong human impacts on the Earth didn’t start and didn’t end with the industrialization. Propositions ranged between ~15.000 years ago when the agricultural revolution started and 1945 when the first nuclear weapon exploded and at the same time the adverse human impacts on the Earth began to accelerate. People of the International Commission of Stratigraphy are working on it. Questions they need to answer are: Which human actions will stay preserved in the geological record? And: What would come after the Anthropocene? Because of unanswered questions, the Anthropocene is still not an official part of Earth history and possibly, it will never be.
But from a moral, non-geological perspective, why would it be important to officialize the Anthropocene? Do we need to have it black on white that we are screwing up our planet? I think most people know now that things on Earth have gotten bad and are still getting worse. Not only scientists know that. Our actions to protect the planet should not be dependent on if we have an official term for the time of humans. Still, it makes sense to define a new era, especially morally. It can be a wakeup call, a motivation to change things. Although the Anthropocene is not an official term yet, it is probably much more popular than most of the other official geological terms 😉 It is established in our society and many people use it when talking about the time of humans. So, although it is hard for scientists to find a consensus, the conversation about the Anthropocene itself has an eye-opening effect on the short-term effects of humans in the history of Earth and on the actions we should take to make things better. For the future I see two main options: Either we continue to destroy the Earth and eventually the human population will collapse, which will let the Earth recover, or we initiate sustainable changes now to safe the Earth and ourselves.
Crutzen, P. J. 2002. Geology of mankind. Nature 415:23.