Over 99% of all life to have ever lived on this planet is now extinct.
The number is so extreme, so mind-boggling to our limited senses of perception that it's hard to wrap one's mind around the concept--but it's true. Through life's long and varied history, we (and all life that shares this planet with us) are the slightest fraction of a fraction of what once was.
Throughout life's history, there have been five major mass extinctions--in each of these catastrophic events, 50% or more of life on the planet was wiped out in a geologic heartbeat. The latest of these was the famed KT extinction event 65.5 million years ago, in which the reign of the non-avian dinosaurs came to a cataclysmic close. It was this extinction that those all too familiar furry creatures, the mammals (who, while existant, grew no larger than an opposum while the dinosaurs filled the niches of the dominant terrestrial group) were allowed to diversify and flourish.
And thanks to this diversification, I'm here to type these words today.
(diagram shows the extinction rates as a percentage of major marine biological families over time; in millions of years--note the five massive spikes)
The causes of these extinctions are still relatively little known--a variety of factors have been suggested for all (one of the more understood of these extinctions, the prior mentioned Cretaceous-Tertiary extinction is commonly believed to have been the result of a massive impact event, in which an asteroid the size of Mount Everest slamming into what is now the Gulf of Mexico, leaving a thin layer of Iridium--a substance remarkably rare on Earth, but very common in asteroid bodies).
The mother of all mass extinctions, the Permian-Triassic extinction (in which 96% of all oceanic species combined with 86% of all terrestrial species were wiped out) took place 251.4 million years ago. It holds the unique status of being the only known mass extinction that involved a heavy blow to the world's insect species.
Many important things were happening at once--increased volcanic activity, the fusion of the continents together into a single mass, combined with massive drops in Oxygen and enhanced levels of Carbon Dioxide (which in turn contributed to a probable climactic shift). Which of these factors was the primary contributer is still harshly debated--but if there is one thing we can agree upon, the effect it had on life on this planet was monumental.
It was quite literally almost the end of multi-cellular life as we know it--but over vast stretches of ever creeping time, life steadily recovered from its near downfall and re-diversified and eventually came to flourish once again.
It is very probable--in fact, almost certain, that we are in the stages of a sixth great mass extinction. Due to extensive loss of habitat, pollution, and extreme warming of the Earth's surface we are losing an estimated 50-150 species per day.
And once a species is gone, it's finished--never again to return. And though life is resilient (possibly more than we can ever know), it takes on average over a million years for biodiversity to recover from extinction events. Speciation is not a solution any time in the close future.
However, there is cause for optimism--through the course of evolution, we are unique in having the chance for severe impact across much of the Earth's biota--and as much our species can act as an agent of destruction, we have the ability to help fix what we've done. And however much that is possible, I hope we work together to accomplish just that.
GreenRoots is a new environmental series created by Meteor Blades and Patriot Daily for Daily Kos. This series provides a forum for the discussion of all environmental issues, including the need for sustainability and the interrelationship between environment and salient issues of our lives, including health care, family, food, economy, jobs, labor, poverty, equal justice, human rights, political stability, national security and war.
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