The final event happened in a place and time that are part fictional and part real. The exact circumstances will always hide in uncertainty, but somewhere around 1989, the last golden toad in the Costa Rican cloud forest was observed. After that, the story becomes fictional. Hidden in the leaves of the forest, the last golden toad died, its body shredded by a skin fungus. The fungus is real, and it was most likely introduced from Africa by humans as they traversed the globe, carrying with them the seeds of the golden toad’s demise.
The golden toad is not alone. An estimated 168 amphibian species have gone out of existence in the past several decades, and at least 2,469 species (43% of the known amphibian species) have populations in decline. When considering ecosystems, change is often not as significant as the rate of change.
Geologic history is replete with examples of species that went extinct. There is a natural background rate of species extinction. When that rate is grossly exceeded, we refer to it as a “mass extinction.” Amphibians are not particularly well preserved in the fossil record, so their background extinction rate is fuzzy. None-the-less studies, using what data is available, indicate that the amphibian extinction rate is currently as high as 200 times the background rate.
Most people reference five historical mass extinctions. I place the number at eight since I include the original oxygenation of the earth’s oceans as the first primordial extinction event. This was an event that wiped out the existing chemosynthetic organisms who were first-comers to this thing we call life. Oxygen was poison to them.
The great oxygen catastrophe was the second mass extinction event. Cyanobacteria (blue-green algae) were so successful as a species that the oxygen they produced changed the atmospheric composition and sent earth into a deep freeze that almost wiped them and other species out. Following the first two events were the five well-known extinctions: the Ordovician/Silurian event, the Devonian Oxygen crisis, the “Great Dying” in the Permian, an end Triassic extinction event, and the K-T extinction that took out the dinosaurs (Mass Extinction Events: Life’s Struggle for Survival).
The accounting presented above leaves us with event number eight. The eighth extinction event is one that we are getting to see in a very closeup and personal way. It is an extinction event triggered by a single species, a species that has achieved unbridled dominance over the biosphere, Homo sapiens. The Anthropocene is the age of humans. The rapidity with which Homo sapiens have ascended to dominance is unparalleled in geological history. The change from being a small part of the animal kingdom to total dominance has been over thousands of years, not the tens of millions of years that generally accommodate evolution.
Past extinction events have root causes in biological activity, geological activity, and cosmic activity. These extinction events play out in three ways. They can deprive life of essential resources like oxygen or sunlight, produce substances that are toxic to life, or they can evoke rapid climate change that overwhelms the ability of life to adapt.
Human activity is currently fulfilling two of these conditions. Industrial development and greenhouse gases produced by human activity are creating rapid climatic change. Human activity also puts toxins into the atmosphere and the oceans. Global warming directly contributes to the acidification of the oceans from both CO2 absorption in the ocean waters and acidification related to sulfur dioxides and nitrogen oxides thrown off as byproducts of our industries.
Life is tenacious but not invincible. The
Rapid climate change is not a theory; it is a fact. What it means for the future of life on our planet is the debate. The future of many species, perhaps even our own, will be dependent on our ability as human beings to control the rate of environmental change on our planet.
Chemosynthetic life: The first mass extinction (Source: ArcheanWeb) – https://archeanweb.com/2020/04/02/chemosynthetic-life-the-first-mass-extinction/
Mass Extinction Events: Life’s Struggle for Survival (Source: ArcheanWeb) – https://archeanweb.com/2019/12/01/mass-extinction-events-lifes-struggle-for-survival/
Amphibian Decline or Extinction? Current Declines Dwarf Background Extinction Rate, MALCOLM L. MCCALLUM, Journal of Herpetology, Vol. 41, No. 3, pp. 483–491, 2007Copyright 2007 Society for the Study of Amphibians and Reptiles – https://herpconbio.org/McCallum/amphibian%20extinctions.pdf