The Holocene Era is the modern geological period, starting from about 40,000 years ago until the present day. This period has seen the expansion of modern man across the planet, and the effects of that expansion on the biosphere. Pretty much everywhere that man has gone, he has sown destruction in his wake.
The fossil record contains evidence for 5 mass extinctions:
- Cretaceous–Tertiary extinction event (K-T extinction) – 65 million years ago
- Triassic–Jurassic extinction event – 205 million years ago
- Permian–Triassic extinction event – 251 million years ago
- Late Devonian extinction 360-375 million years ago
- Ordovician–Silurian extinction event 440-450 million years ago
There is a great deal of evidence to suggest we are in the midst of a sixth mass extinction event. The 5 previous events were due to a number of causes, and in some cases the exact causes are unknown. In all cases, however, it was some sort of geological process, whether a cometary or asteroid impact, a long ice age or increased volcanism. The Holocene event, however, has a different cause.
Humanity is responsible, either directly through hunting and other forms of exploitation, or indirectly via habitat destruction and other actions, for the destruction of thousands of species of plants and animals. In the 20th century alone, scientists estimate between 20,000 and 2 million species have gone extinct through human actions.
We cause extinction through several means. In habitat destruction, as we alter and/or destroy natural environments, we reduce or eliminate the ability of other species to effectively use that territory. Whether by logging, burning, clearing for crops, or driving through roads and powerlines, the net effect is the same.
Overexploitation is a major issue, and is responsible for, among other things, the depletion of most major fisheries, as well as the disappearance of many species of large animal (megafauna). Over-hunting, over-fishing, and over-harvesting have driven many species to the brink of extinction, and sadly, often past the brink.
With mass migration and exploration, humans have introduced many non-native species into regions, where, without local predators, they can often out-breed and out-compete local animals and plants. Rats and cats alone are thought to be responsible for the loss of many species of large birds throughout the Pacific Islands, especially New Zealand and Hawai’i.
Pollution, whether localized or global (acid rain, greenhouse gases), poisons the waters and soils that are habitat for sensitive species, or leach away needed nutrients. Global warming and atmospheric ozone depletion—major threats to life forms worldwide—are caused largely by air pollution.
As humans have spread around the world, we have brought exotic diseases with us. Global trade is spreading many new diseases, and many species have no defense, and no time to evolve a defense, against these imported diseases.
This current extinction event is thought to have occurred in three waves. The first wave was 10,000 years ago, and included such species as the giant ground sloth, the sabretooth tiger, and woolly mammoth. Over the next few thousand years, human migration led to the extinction of the New Zealand moa, and many other island species. This phase continued until about 1,000 years ago.
The next phase occurred as European explorers, traders, and colonists spread throughout the world, and saw sharp declines in various marine animals, and the loss of many large, flightless birds, along with other species.
The third phase is occurring now, as human over-population and exploitation overwhelms natural environments all over the globe.
As this event unfolds, it is expected up to 50% of all existing species will disappear by the end of this century. This is a catastrophe, and it is entirely on humanity’s hands. At this point, herculean efforts will need to be made to save any of these threatened species, and it is vital the effort is made. Now that we have reached the point in our cultural development that we can identify the problems that we are creating, we need to fix them, as a moral imperative.
In about the time it took you to read this article, 1 species somewhere in the world has become extinct.