Holocene Extinctions

Mass extinction refers to a relatively short period of geological time where a number of biodiversity dies, which consists of species such as bacteria, fungi, plants, mammals, birds, reptiles, amphibians, fish, and invertebrates. In simple geological terms, "short" can cover thousands or even millions of years. Five major mass extinctions are recorded on Earth, which occurred about 65.5 million years ago, when dinosaurs went extinct in the fifth mass extinction. Scientists now classify us to be in the midst of a sixth mass extinction.

Scientists say other extinctions were caused by natural catastrophes, such as volcanic eruptions, collisions with asteroids, and the oxygenation collapse of the oceans. It's a different story with this ongoing Holocene extinction that has been going on for the last 10,000 to 110,000 years. It is very dangerous and irreversible once it takes place. The human population is on the increase and this has resulted in a threat to other living organisms in the ecosystem through overhunting, exploitation for wool and leather, or the total effacement of green areas by urbanization, changing climate, pollution, among other challenges. Thirty percent of the species alive today will be lost in the next 40 years, and it would not come as a surprise if humans themselves are to be deleted in this extinction due to their destructive activities.

Conservationists call the Holocene extinction being caused by humans as an Anthropocene extinction. Like earlier mass extinctions brought about by global-scale habitat destruction caused by an event such as volcanic eruption or meteorite impact, habitat destruction plays a big role in the ongoing sixth mass extinction. Alternative lands can be found, and habitats can even be controlled for use in agriculture so as not to lose habitats and, therefore, the impacts on the flora and fauna. There is a need to regulate and control overconsumption of certain animal groups for food, and overhunting must be restricted under laws with continuous monitoring.

Aside from habitat losses caused by humans, one of the most destructive agents for habitats has been climate change. Inhibition of the consequences of climate change will thus go a long way toward slowing down the current mass extinction. This can be achieved by controlling fossil fuel usage, reducing greenhouse gas emissions, finding alternative energy sources, and ways of capturing the greenhouse gases in the atmosphere.

Extinction is a natural process. Species die out or evolve over time. We know that on average, during Earth's history, one species died out each year for every million species based on fossil evidence. This would imply that we would expect 10 to 100 species to go extinct annually, depending on which part of geological history we are dealing with. This has been termed the background extinction rate. But it is not: modern extinctions occur at a much higher rate than the background rate. Take the example of the mammalian species average lifespan, which is about one million years before it becomes extinct or evolves. In the last 400 years, 89 species of mammals have become extinct, which happens to be almost 45 times the rate of the background extinction rate.

Mammals aren't alone with this trend. A loss of genetic diversity in vertebrates, invertebrates, plants, fungi, and other living creatures is shown to have a very high extinction rate, which is now ranging between 1,000 and 10,000. According to a paper published in 2017, nearly one-third of all known vertebrate species were declining in population size and range. Another study showed that 3,000 different species had seen half of their populations shrink since 1970. Should this continue, then 30-50% of the total species could be headed to extinction by the middle of the century. This statistic has only been seen one time in Earth's history; this occurred when there were mass extinctions.

Species loss that was identified at that specific time include:

The dodo (Raphus cucullatus) of Mauritius, extirpated mainly by the arrival of rats and pigs that could feed on this giant flightless pigeon's eggs and young. This species is known to have died out some time before 1662.

Hunting to extinction: The Great auk (Pinguinus impennis) was a large flightless sea bird of the North Atlantic. It is impossible to identify any last definite date of the species being seen; but the last definite record was when on July 3, 1844 a sailor recorded wringing the necks of two.

Stellar's sea cow (Hydrodamalis gigas), an 8-10 meter long manatee-dugong relative, was first known to Western science in 1741 and hunted to extinction within 27 years by whalers.

Other dramatic extinctions during the Holocene occurred in:

Madagascar: Humans arrived between 350 and 550 CE, and through habitat destruction and hunting, wiped out species such as the elephant bird (Aepyornis maximus), two species of dwarf hippopotamus, and several large-to-giant lemurs.

New Zealand : Once Polynesians settled there in 1280 CE, they quickly exterminated species including nine species of moa (Dinornithiformes) and Haast's eagle (Harpagornis moorei), one of the largest birds of prey ever.

Tasmania: The settlement of Tasmania in 1803 led to the systematic extermination of the Tasmanian people and the Tasmanian tiger (Thylacinus cynocephalus).

Continental North America also lost an enormous amount of species including :

The passenger pigeon, that was once the most plentiful bird species, was exterminated by the end of the 19th century, mainly due to habitat destruction and commercial large-scale hunting. The last pigeon, "Martha," died in 1914.

The Carolina parakeet also went to extinction in the early years of the 20th century; it was in 1918 that the last surviving individual of the species, "Incas," died.

The ivory-billed woodpecker, Campephilus principalis, became extinct by 1944 due to excessive logging of its habitat.

Major contemporary causes of extinction include:

• Overfishing, making commercial fisheries collapse throughout the world.

• Habitat destruction for agriculture, logging, development, reducing habitats for other species.

• Freshwater habitat loss due to draining lakes and damming rivers.

• Eutrophication from fertilizer runoff, turning coastal areas into "dead zones."

• Ocean acidification, weakening calcifying organisms like corals and mollusks.

Earth is probably on the brink of its sixth mass extinction, given the impact of human activity on the marine domain and on small things and a lot else besides. As with other mass extinctions, environmental shifts are proceeding at a pace too high for organisms to evolve fast enough to keep up. Current extinction rates aren't yet comparable to the Big Five, but the same sort of causes-try thinking extreme eutrophication and ocean acidification-are operating.

A recent discovery in April 2018 was that the broad public hugely underestimates the plight of famous and "charismatic" species.

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