There may be disagreements on the causes of mass extinctions but one thing is certain that mass extinctions had catastrophic effects on the living organisms of those particular times. Until now 90 to 97% of all species that ever existed went extinct. No doubt there are strong evidences of bolides impacts in different times that some of them coincide with mass extinctions, the most famous one is Chicxulubm impact crater that is coincided with K-T boundary or Cretaceous-Tertiary mass extinction. Similarly the Hydrogen Sulfide that is deposited by action of anaerobic bacteria may cause mass extinctions. Beside movements of plates causing volcanic activities or accretion of large pieces of lands to make supercontinents cause hot house and cold house periods. All of these processes in some way were proved to be catastrophic for organisms living on those times. But the question is, is these mass extinctions stopped or reversed evolution or favored evolution. The Paleontological record clearly shows that catastrophes favor evolution. We observe a rapid growth of newly evolved organisms after each mass-extinction. The rise of reptiles after Permo-Triassic and the rise of mammals and flowering plants after Cretaceous-Tertiary mass extinction is two famous examples that majority of the people are familiar. What is driving the rapid rate of evolution after mass extinction? Certainly, the empty space and energy sources that are left by earlier organisms are the incentives for the developments of new set of adaptations to get benefits from. Again energy is driving evolution.
1- Mammals were existing throughout Mesozoic era but this era were the era of dominance of massive reptiles and Dinosaurs. Mammals were smaller in sizes. During the K-T mass extinctions all animals weighing more than 50 Kilograms went extinct. As mammals were small in size throught of the Mesozoic era, so this mass extinction that killed massive reptiles provoide space and energy available to smaller mammlas and mammals rapidly evolved and diversified soon after K-T mass extinction and throughout Cenozoic period.
2- Reptiles just gulp their prey which is not an efficient use of nutrition. On other hand mammals articulation of jaws and diversification of teeth for crushing, tearing and cutting the food and get more calories from the food. These effecient extraction of energy as well as diverfication of diets made mammals able to survive extinction as well as to diversify in post extinction era.
3- Synapsids (Mammal like reptiles) and trilobites went extinct during Permo-Triassic mass extinction so as a large part of forests that become abundant in Carboniferous but fungi flourished during this mass extinction event as decaying forests were provoiding anormous amount of energy. It is known as Fungi Spikes.
4- We see a similar spikes in the K-T mass extinction also, soon after mass extinction, first Ferns dominate, then gymnosperms and lastly angiosperms.
5- Therapsids (Class Synapsida, Order Therapsida) become dominant two times. It became dominant in Permian period but the by Permo-Triassic extinction it declined and it ramained an insignificant group until the Dinosaurs were rulling on land. By extinction of Dinosaurs in K-T mass extinction, it became once again dominant. These two successes were possible because of diversification of teeths and exploitations of energy of diverse foods more efficiently.
Darwin's Finches as an example of catastrophe
Word catastrophe is controversial between evolutionists and creationists so we first define the catastrophe for our usage, "Catastrophe is a sudden change in the environment". Darwin observed that finches in Galapagos have varying sizes of beaks that were specialized for eating different sizes of seeds. Darwin's observations is actually confirming that energy drives evolution. Finches main source energy were seeds ( Some finches are also specialized to eat insects and suck blood. Finches with thick and short beaks specailized in cracking seeds. Finches with relatively thinner and longer beak specailized to hunt on insects and still finches with more thinner and longer beaks specailized to suck blood of other larger birds.) so they specialized their beaks accordingly to not be in competition with each others but despite use all possible energy sources (here seed sizes).
El Nino Event of the 1982- 1983 le to a ten years of the change in habitate and plant composition of the Daphne major isalnd (One of the famous Galapagos islands). These changes in Galapagos islands also changed the availability of different seed sizes. B. Rosemary Grant and Peter R. Grant studies showed that after sever El Nino event of 1982-1983 hybrid fiches survived better than their parental species. The hybrid finches had the intermediate beak sizes relative to their parental beak sizes.
Catastrophe could be very local like acidification of a pond or eutrophication of a lake to global scale like global warming.
Evidence of rapid climate change (Catastrophe)
A press release ( 35/08) of National Environment Research Council (NERC) entitled as, "Rapid Climate Change: past; present; future" (http://www.nerc.ac.uk/press/releases/2008/35-rapid.asp)
starts, "Most climate models predict gradual future changes to climate, related to the steadily increasing greenhouse gas concentrations. But ice and sediment core records reveal that, in the past, climate has changed abruptly - possibly in as little as 10 to 20 years. Such rapid change in the future could make prevention and adaptation strategies difficult and expensive to implement."
Citing the research in arctic it explains, "Research results from the programme revealed that, around 8,000 years ago, Newfoundland, the UK and northern Europe experienced extreme cold and dry conditions. Greenland temperatures were almost 6°C colder than present day. The shift to colder temperatures took only a few decades and lasted for about 160 years. It is thought that a rush of melt-water into the North Atlantic caused the slowdown of the Atlantic conveyor, leading to the colder conditions."
Global warming
Global warming is a hot issue. Certainly there are environmental activists and industrialists who conflict each other on a lot of issues. It is beyond any conflict that anthropogenic pollutions and misuse of natural resources, lands, oceans, lakes, rivers, wetlands, glaciers etc have not only endagered a lot of species but also threatening and costing human health. It is also beyond the doubt that there must be researches, legislations, monitoring and restoration of natural environments.
BUT
The big question arise from the geological history. In geological past when there were no human so everything were natural again we observe cyclic periods of cold and warm ages. Besides we observe evidences of mass extinctions. Though we have not to worry much about them as they occur in geological time scale (millions of years) but still what about a meteorite impact that is more swift and quick? What is our preparation or atleast some solutions for them?
An important point:
In our times we observe that tropical regions are abundant in both number of species and diversity of life forms and as we go towards poles the number of species and their diversity decreases. As global waming and anthropogenic pollutions and habitate disturbance is forcing a lot of organisms towards the extinction the most rapid rate of extinction is seen in tropics where life is most abundant. So naturally a question arise, that in geological past time when catastrophic forces were pushing the organisms towards extinction, were they affecting the tropical area with high intesity than polar regions with least diversity of life forms?
Based on the uniformiterian principles, certainly it was the case. Tropical regions had higher rates of mass extinctions as well as higher rate of mass recovery or spikes in post mass extinction events than polar regions. Temperature, nutrient availability and heavy precipitations are few factos that make tropical regions an engine of extinctions and recovery of life forms.
In other words tropical regions have higher energy levels so it has higher rate of evolution and polar regions has low energy levels and hence low rate of evolution.
External Links:
1- http://science.nationalgeographic.com/science/prehistoric-world/mass-extinction.html
2- http://www.esajournals.org/doi/abs/10.2307/2265625
References:
1. B. Rosemary Grant, Peter R. Grant, High Survival of Darwin's Finch Hybrids: Effects of Beak Morphology and Diets, Ecology (Journal) 1996 77:2, 500-509 (Pages)
This was part of my effort to rethink evolution. Feel free to criticize, suggest points and comment...
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