Extinction and Time
Questions:
- What causes mass extinction of life forms?
- How massive are the losses for some of the more dramatic extinction events?
- How does life respond to such events?
- Is it reasonable to expect that the Darwinian form of evolution 'replaces' species after each event?
- Is there enough time to explain life's reemergence through evolution?
Short Answer :
This portion of the 'Window' has yet to be filled in. So, this is in part a place holder for a more comprehensive treatment of this topic. Yet, we did not want to leave the topic unaddressed.
The questions above are important and science is today still learning more about the causes of massive extinction events that appear at several points in geologic time. A comet or asteroid hitting the earth is the specific causes for at least one of these events. This is something science has documented and the larger extinction events is associated with a very large object impacting the earth.
The planet is marked by numerous craters and there is even some concern today for the potential of a large impact to occur sometime in the future. What has stopped out planet from being continually bombarded is the powerful gravitational attraction of Jupiter. You might think of this larger planetary cousin as the 'great attractor' that serves to sweep up many of the meteorites or asteroids that might otherwise be earth bound.
Yet, impacts have occurred and the fossil record provides evidence for massive losses of life. What is a most important point is how extinction events put a wrinkle in the standard evolution story. Remarkably, the return of life to the planet after the larger events seems nearly instantaneous in geologic terms. Within thousands of years dinosaurs reappear after an earlier event. The types or kinds differ from what was on Earth before the extinction event. Also, remarkably, the new set of species is well suited for the earthen conditions they inherit.
In short, Darwinian evolution cannot account for the rapid reappearance of these animals. This point is glossed over in many places, books, museums, etc., leaving us to note that the assumption of evolution is strong and unjustified.
But even then, natural rates or current rates of extinction do not seem to be paralleled by increases in numbers of species, even without the catastrophic events that we'll consider here.
Keep the questions above in mind as you work through the science area. They are important to building the overall larger picture.
Consider This :
We know of multiple extinctions of life, dinosaurs more than once, where life reappears in the blink of geological time. As a scientist sitting among scientists, might one wonder why the question is not addressed head on: "Where is the time in ten thousand years to evolve all the new dinosaurs?" And yet twice it appears to have happened that rapidly. Well?
And while many turn a blind eye to the appearance of life with the Cambrian explosion, few outwardly recognize that flowering plants appear in the fossil record with only a faint whisper for a predecessor. A wide diversity of flowering plants comes in relatively rapid order. Any antecedent found to date is again little evidence for a diverse horizon of life appearing with little connection to the past.
Added Perspective:
(090109)
References of Interest
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