The sixth great extinction |

The sixth great extinction

Hal Sundin
Staff Photo |

From its very beginning, the survival of life on this planet has been fraught with uncertainty. From the study of fossils, paleontologists have identified that there have been five massive extinctions of life forms on our planet in the 500 million years since the explosive proliferation that took place during the Cambrian Period. There may have been other earlier extinctions since life first appeared on Earth as long as 3 billion years ago, but there is no fossil record of their occurrence.

The end of the Ordovician Period, about 440 million years ago, marked the first great extinction. It is believed to have been caused by a prolonged ice age that caused massive glaciation and lowering of sea levels, and resulted in an estimated 60 percent extinction of all sea life, which was all that existed at that time.

The second great extinction came at the end of the Devonian Period, the age of fishes, about 365 million years ago. It also was brought on by an ice age, and resulted in an estimated extinction rate of 70 percent.

The third great extinction was the most drastic, destroying 90-95 percent of all animal life. It occurred about 225 million years ago at the end of the Permian Period, and was the result of massive volcanic activity that created an enduring worldwide winter.

The fourth great extinction, at the end the Triassic Period, about 210 million years ago, resulted in the annihilation of about half of all animal life, including most ocean reptiles and many types of amphibians, and is believed to have been caused by volcanic activity and possibly a comet collision.

The fifth and most recent great extinction, which occurred at the end of the Cretaceous Period 65 million years ago, is the best known. It was caused by an asteroid or huge meteorite that landed near the Yucatan Peninsula, and created the long-lasting night that destroyed the dinosaurs and marine reptiles, but amphibians and early mammals and birds survived.

Naturalists are concerned that we are presently well into a sixth great extinction, different from any of the previous five, in that it is not a result of a natural catastrophe like volcanic action, an ice age, or a comet or asteroid collision. Instead it is being caused by overwhelming human numbers and activities as the world population has exploded from 1.5 billion to nearly 7 billion in just the last century, and appears to be headed toward 9 billion or 10 billion by the end of this century.

This Sixth Extinction is occurring at a rate of 50,000-100,000 species per year, and rising, and could become the most severe of all. It is feared that fully half of the species that existed two centuries ago will be extinct by 2100. Explosive human population growth from 3 billion in 1960 to more than 7 billion today has caused the destruction and fragmentation of millions of square miles of crucial habitat, and with it, the extinction of half of the world’s species.

Deforestation for food production, commercial agriculture, mineral extraction and fuel is the primary cause. Overfishing and bottom destruction by trawler drag-netting have reduced the numbers of important food species of fish by 90 percent. Illegal hunting of elephants for their tusks (30,000/year) and rhinoceros for their horns (1,000/year), driven by soaring prices, will lead to their extinction well before 2050. Tiger numbers have declined 95 percent to just 3,500, from poaching for their body parts, which in the Orient are falsely believed to have medicinal value. The Japanese kill 100 million sharks a year just for the fins to satisfy their craving for shark-fin soup. The survival of polar bears and many other species is threatened by human-created climate change which is occurring at too rapid a pace for them to be able to adapt. Ocean acidification and warming resulting from burning fossil fuels can diminish the numbers of plankton, which are a key link in the ocean food chain and produce half of the oxygen necessary for the survival of most animals, including us.

The implications for the future are alarming. In the balance is the survival of mankind, whose ability to feed itself may also be endangered by shortages of the energy and resources needed to produce food. It is time for the world to wake up to what is happening and take the actions necessary to rein in our numbers and impacts that are causing the escalating rate of extinction, which if not checked, may also include us.

“As I See It” appears on the first and third Thursdays of the month. Hal Sundin lives in Glenwood Springs and is a retired environmental and structural engineer. Contact him at

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