Most extinctions that have occurred throughout Earth's long history have been a result of natural factors. However, recent evidence suggests that human-made factors may be the cause of many extinctions arising today.
Are we currently experiencing the
6th Mass Extinction?
At least Five times in Earth’s history 75% or more of all living species disappeared forever — and within a short period of time. These mass-extinction events marked the boundaries between different periods in geologic time. Those species losses caused a major shift in the planet’s ecology and biological evolution. Clues to these changes can be seen in the fossils and rock layers that form Earth's geologic record.
Today, human activities appear to be driving species to go extinct at a rate never before seen!
Extinction is a perfectly normal phenomenon. Species either die out or evolve into something new over time. From the fossil record, we can tell that the average rate of extinction per year throughout Earth's history is around 1 species per million species per year. That means that we can expect anywhere between 10 and 100 species to go extinct every year. This is called the background extinction rate.
Unfortunately, extinctions in the world today appear to be occurring on a much higher scale than the expected background extinction rate.
- Take mammals, for example. From the geologic record, we know that the average lifespan of a mammalian species is about 1 million years before it goes extinct or evolves. In the last 400 years, however, 89 species of mammals have gone extinct. That's almost 45 times the background extinction rate.
- When we look at loss of vertebrates, invertebrates, plants, fungi, and other living things, the extinction rate is even more dramatic becoming somewhere between 1,000 and 10,000 times the normal rate of extinction!
- A 2017 study looked at almost half of all known vertebrate species and found that about 1/3 are decreasing in population size.
- Another study found that 3,000 different species had all lost 1/2 their entire population since 1970.
If this keeps up, 30-50% of all species in the world could be in danger of extinction by the middle of the century.
What Can We Do?
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Topic Tips
- Evidence suggests that in recent geologic time many species have become or are becoming endangered or extinct at a rate much higher than expected.
- Evidence suggests that human-factors of extinction appear to be contributing to the current extinction rates.