The following diagram shows the number of organism species present on Earth since the Cambrian radiation. The mass extinctions can be seen when this plot has sharp declines. There have been 5 major mass extinctions, of which it can be seen that the drop of families at the Permo-Triassic boundary has been the greatest.

This event has been extensively studied, and currently it is believed that a combination of things contributed to its severity.

The most important of these was a short time outgassing of CO2 from the ocean floors during unusually severe volcanic eruptions about 250 million years ago. The sudden release of large quantities of CO2 directly killed many marine organisms by carbon dioxide poisoning.

The largest eruption of the 20th century, Mt Pinatubo is tiny compared to the Siberian Traps but caused a 0.5 degree drop in global temps the year after it erupted. The largest eruption in historic memory occurred on Iceland in 1783-84 spewing out 12 km3 of lava onto the island (the Siberian Traps erupted about 3 million km3). The poisonous gases given out are recorded as killing most of the islands crops and foliage and lowering global temps by about 1 degree. If events this size can affect temperatures and large areas then the effects of a large scale flood basalt are incomprehensible.

Could such events cause or add to a mass extinction event?

The sudden increase in greenhouse gases produced a large increase in the amount of heat trapped by the atmosphere.

This produced a heat spike of 5 to 10 degrees persisting for 10 to 100 thousand years which killed off large amounts of terrestrial life.

Currently this event is believed to be a double or triple cause event spread over nearly 100,000 years. A CO2 increase caused by the silurian traps volcanic activity, a possible impact added to the problem of ~ 5 degree temp. increase, causing an ocean temp increase that released huge amounts of Methane (a strong greenhouse gas) producing a addnt 5 degree for a total of 10 degree increase – sufficient to kill most organisms on land or sea.

This was a significant event eliminating about 50 % of genera, especially destructive to marine life. This was thought by many to have been an impact event, but there is currently no identified impact site associated with this event. The Manicouagan Crater in Quebec is about 100 km in diameter and of the correct size, however it is currently dated at 214 million years, which is too early. There are environmental changes associated with this period, but nothing of a severity to produce the observed effect. Its probable cause remains unknown.

The end-Triassic mass extinction : 202 million years

This mass extinction event, resulting in the death of the dinosaurs, is one of the most well known extinction events. A team of scientists directed by Luis Alvarez proposed that this was an impact event occurring about 65 million years ago. This was based on evidence of large iridium concentrations found at several sites around the world, and an association with high iridium concentrations in many meteorites.

The Cretaceous/Tertiary boundary event : 65 million years

Based on this, and other evidence, it is widely accepted that an approximately 10 km diameter comet or asteroid struck the ocean off the coast of Yucatan blasting a crater between 180 to 300 km wide and precipitating a chain of events exterminating the dinosaurs and over 50% of other species on Earth at that time. The impact, in addition to shock waves and massive fires, produced major and long lasting climactic changes.

Based on all of this information one would assign a very small fraction to fme since the evidence indicates that significant mass extinctions are not uncommon in a planet’s history. A value of 0.000001 will be assumed, i.e. a one in a million chance!

If we assume ~ 400 billion stars in the Milky Way galaxy, and assume 4 planets per star, then the likelihood of finding a planet with all of the requisite requirements for complex life to develop, evolve, and survive would be.....

(4x1011)*.003*.01*.027*.2*.5*.001*.13*.08*.005*1x10-6 or about 0.0000000017 =1.7x10-9 in our Milky Way galaxy.

Based on extremely optimistic values for the various factors in the Rare Earth Equation.

Even assuming ~ 1012 galaxies and and 4 planets per star yields

6.7 x 103 planets out of 1.6x1024

planets or 1 part of 4,000,000,000,000,000,000,000

for the probability of the correct system arising by chance!What reasonable conclusion should one make?

Recall that the estimates made by supporters of SETI are much more optimistic and generous......yielding much larger numbers..

One such estimate gave 100,000 radio communicating civilizations currently active in the Milky Way galaxy.

That figure of 100,000 would mean there is one radio-emitting civilization right now per 4 million stars -- reason enough to tune in on the heavens and start hunting for them. If they were scattered at random throughout the Milky Way, the nearest one would probably be about 500 light-years from us. A two-way conversation would require a time equal to a good part of recorded human history, but a one-way broadcast might be audible.

However, 50 years of SETI have failed to find anything, even though radio telescope apertures, receiver techniques, and computational abilities have improved enormously since the early 1960s.

Granted, the "parameter space" of possible radio signals (the possible frequencies, locations on the sky, signal strengths, on-off duty cycles, etc.) is vastly larger than the tiny bit that has yet been searched.

But we have discovered, at least, that our galaxy is not teeming with powerful alien transmitters continuously broadcasting near the 21-centimeter line. No one could say this in 1961!

According to many life scientists, it is naive to suppose that the evolution on another planet should necessarily result in intelligence as we know it.

In his bestseller Wonderful Life, paleontologist Stephen Jay Gould (Harvard University) asserts, "We probably owe our own existence to . . . good fortune. Homo sapiens is an entity, not a tendency."

“..if we could rewind the tape of biological evolution on Earth and start over, it is impossible that humans would again appear on the scene. We are the result of too long a chain of chance flukes and happenstance.”

Evolution is unpredictable and chaotic. Gould has pointed out again and again that..

Our notion that the increase of biological diversity is necessarily accompanied by an increase of mental capabilities may be dead wrong. If some recently evolved animals are bigger and smarter than any earlier ones, that could just be a fluke. Human levels of planning and technology may be even more so. There are no firm indications that increased intelligence is an inevitable product of biological evolution.

Gould notes that there is no overall pattern in evolution, no preferred direction.

Contrary to popular belief, the fact that intelligence has arisen once tells us absolutely nothing about how often it happens -- for the simple reason that we ourselves are the one case! We are a self-selected sample. Even if intelligent life is so improbable that it appears just a single time in one remote corner of the universe, we will necessarily find ourselves right there in that corner observing it, because we are it.

"Physicists still tend to think more deterministically than biologists," wrote Mayr in the May 1996 issue of The Planetary Report.

"They tend to say that if life has originated somewhere, it will also develop intelligence in due time. The biologist, on the other hand, is impressed by the improbability of such a development."

Based on almost any reasonable criteria that one could devise, the existence of intelligent life on Earth

and perhaps in the Universe as well

is an ENIGMA....

without GOD