From Holocene to Anthropocene: tracing human influence on Earth

The planet Earth has existed for about 4.5 billion years, and life first emerged at least 3.5 billion years ago. Modern humans evolved approximately 200.000 years ago. 

To put these timescales into perspective, you can imagine the whole history of life compressed into one year. Then, if life began on January 1st, modern humans arrived on the scene about 11:30 pm on December 31^st. So we are very recent inhabitants of the planet.

Over the history of Earth, the climate has varied a lot. For most of the time, Earth's climate has been quite warm. There have been five colder periods, called ice ages, that are characterized by permanent ice caps at the poles. Currently, we are still in the latest ice age, called the Quaternary. The Quaternary ice age started approximately 2.58 million years ago, and it still continues, as the Antarctic and Greenland are covered by thick layers of ice. 

Within the Quaternary ice age, the temperature has not been constant but has fluctuated between colder periods called glacials, when the ice sheets have extended to lower latitudes, and warmer periods called interglacials when the ice sheets have retreated towards the poles. The temperature in the interglacials has been several degrees warmer than during the glacials. The regular fluctuations between glacials and interglacials have been driven by regular variations in Earth's orbit that change the distribution of solar radiation between latitudes in each season (we will look into these in more detail later in the course). The variations in the Earth's orbit are very slow and are not the reason for the current climate warming. We will look into climate change also later in the course.

The glacial periods have been quite long, lasting approximately 70.000 – 90.000 years, while the interglacials have been shorter, lasting approximately 10.000 – 20.000 years. The current interglacial – called Holocene – started approximately 12.000 years ago. The Holocene is characterized by extraordinarily stable global surface temperature, with the mean annual temperature remaining within approximately 1°C for more than 11.000 years, until the onset of the current, human-caused rapid climate warming.

Interestingly, however, it seems that the human impact on climate started a long time before the industrial era. It has been suggested that carbon dioxide and methane emissions from deforestation and farming in Europe and China already 7.000 – 5.500 ago contributed to the stable (or slowly increasing) global temperature in the latter part of the Holocene.

Whatever the reason for the climatic stability of Holocene, it has certainly contributed to the success of human populations by allowing people to develop agriculture, establish permanent settlements, increase population sizes, and kick off the cultural and technological development that have amounted to e.g. the internet, artificial intelligence, advanced medicine, and the atomic bomb. The extraordinarily stable Earth of the Holocene is the only Earth human civilization has ever experienced. 

Now it looks like the stable conditions of the Holocene may be coming to an end. This time the end of the interglacial is not due to the oscillations in the plane of Earth’s orbit but to the heavy human impacts on Earth’s nature and climate. Geologists study Earth's history by studying layers of rocks and sediments and define distinct periods and epochs by e.g. the types of fossils found. Now many scientists suggest that the human impact on Earth’s biological and geological processes has become so significant that it will leave a distinct record in sedimental strata, and that that we are no longer in the Holocene, but have entered a  new epoch tentatively named Anthropocene, the human era. 

The epoch of human domination

The word ‘Antropocene’ comes from the Greek words ‘anthropos’, meaning ‘human’, and ‘kainos’ (scene), which refers to ‘new’ or ‘recent’. The concept was popularized by chemist Paul Crutzen and biologist Eugene Stoermer. They used the concept to describe the increasing human impact on the planet and suggested that this time of human domination should be distinguished as a geological epoch following the Holocene.

Anthropocene as a scientific concept is controversial since both its definition and starting point as an epoch are disputed between different disciplines. Many have also critiqued the concept of treating humankind as a homogenous group, where all humans have a similar influence on Earth. In truth, developed countries face much more responsibility for the excessive use of natural resources than less developed ones.

It is nevertheless indisputable that the human species has greatly influenced our planet and the wellbeing of both humans and other species. This has led to global crises such as climate change, climate-induced immigration, and the loss of biodiversity (the diversity of biological life on Earth).

We do not yet know what the future of the Anthropocene will look like, how long it will last, and if there will be human civilizations to record it, but we are still in a position to influence its conditions. Tackling global crises such as climate change and the loss of biodiversity require novel environmental actions, such as radical changes in energy production and consumption. In order to stop the mass extinction of species, it is necessary to diminish the harmful effects of land use on nature. These environmental actions will be further discussed in the forthcoming sections of this course on an individual, societal and cultural level.

In the following sections, we will look into two of the most dramatic current developments on Earth that are driven by human actions: the loss of the biological diversity on Earth and the ongoing climate change, and how they affect humans and the rest of nature. 

For reflection: what is your perception of the role of humans on Earth, and where does this perception come from?  You can share your reflections and discuss with other course participants on the page linked below.

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