In Montana, at a dig supervised by celebrated paleontologist Jack Horner, Nan Crystal Arens from Hobart and Smith Colleges carefully examined the fossil leaves and pollen from a slice of the Hell Creek formation at many different levels. The Hell Creek formation is set just above the K-T boundary and represents the millions of years just before the extinction of the dinosaurs. Dr. Arens found that the number of different species of plants, especially flowering plants, declined significantly as one got closer to the boundary. Perhaps 90% of all the flowering plants had already died before the asteroid struck. Since these represented a large portion of the herbivore dinosaur's food supply, and herbivore dinosaurs were in turn food for the carnivores, this might have caused a sharp decline in dinosaur populations even before the disaster.
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Introduction
About 65 million years ago some event took place that wiped out more than half of all life on Earth. In addition to this mass extinction there was a major face-lift for the Earth as a planet. The continents were shoved to new locations, and inland seas moved on and off the continents, as major ridge expansion took place, particularly in the Atlantic and Indian Oceans. In the process there was major mountain building, volcanic eruptions, and some places sunk beneath the sea, while others rose from the sea. There is evidence of massive destabilization of the oceans and atmosphere. Powerful storms wreaked havoc as indicated by vigorous erosion and greatly increased continental weathering. Some elements, known as isotopes, show drastic shifts in abundance. Masses of sand, clay, and mud deposited layers everywhere, while other areas show missing sedimentary layers. The oceans show rapid desalination events, temperature transitions, and chemical changes.
The Late Cretaceous was the last for the dinosaur, and its close was the most catastrophic of any period in the history of life on Earth. More than one half of all the species on Earth became extinct. In some places 75% to 90% of the life forms vanished from the scene never to be seen again in the fossil record. With the close of the Cretaceous there came the wholesale extinction of large marine creatures. Here was the end of one of the most successful life systems in all of Earth history. What was it that overwhelmed the Earth?
Volcanic Eruptions - The Deccan Trapps:
The basaltic lava eruptions of the Deccan Trapps of western India (the Deccan is a region of India, and 'trapps' comes from a Dutch word meaning 'staircase'.) was mentioned as a possible source of the iridium found in the K/T boundary "iridium spike." It has been proposed that the outgassing, combined with possible explosive episodes, could have been sufficient of itself to have caused the same kind of a "Nuclear Winter" scenario as proposed for the giant meteor impact.
While this possibility cannot be easily refuted, it seems unlikely, given the nature of the lava flows that make up the Trapps. These flows were caused when the Indian subcontinent passed over the Chagos Archipelago plume as India drifted north to collide with Asia. The Deccan Trapps were produced over a span of some 500,000 years by basaltic fissure flows, very similar to the eruptions that regularly occur in Iceland. Basalt has little trapped gas in it, and tends to erupt non-explosively; rather flowing smoothly, and sometimes nearly continuously, much like the current round of eruptions in Kilauea, Hawaii. Where plumes lie under continents, they do tend to produce occasional, but very infrequent, explosive events, leading to the formation of a caldera, which eventually fills in with fissure flow basalt. Yellowstone National Park lies in just such a caldera, and sometime in the next few thousand or tens of thousands of years, Yellowstone will be covered over by fissure flow basalts. The basalts of the Snake River Valley mark the location of past calderas, now obliterated by fissure flow lavas. In fact, the Snake River Basalts and the Yellowstone Park are a currently active example of exactly the process which formed the Deccan Trapps. This process is really quite common in the geological history of the Earth, and only coincidently seems to be associated with a mass extinction. Certainly we are not suffering, nor have suffered in the recent past, from an ecological collapse caused by the Snake River Basalts or the Yellowstone Caldera.
Extracted from: http://webspinners.com/dlblanc/paleo/dino-colo/extinction/other.php
‘Increased Gravitational Pull’ Theory
Another theory offers that during the age of dinosaurs, gravitation on Earth was lighter than today. Hence, all objects and living things were lighter. 65 millions years ago, suddenly, the gravitation increased. Dinosaurs became too heavy and as they were unable to adapt, they died. Mammals, powerful and agile in spite of their smaller size, survived. Reptiles survived also because they appeared during a time gravitation was more important than during the Dinosaurs' age. Birds survived because the augmentation of gravitation made the atmosphere heavier - as a paradox it was easier for birds to fly. Major problem with this theory is the "gravitational constant" put forth by Sir Isaac Newton, which determines that gravitational pull does not change.
Extracted from: http://www.sir-ray.com/Dinosaur%20Extinction%20Theories.htm
+ INCREASE OF GRAVITY =
Contents Page
Page 2) Introduction
Page 3) Asteroid Theory
Page 4) ‘Increased Gravitational Pull’ Theory
Page 5) Super Volcano Theory (Deccan Trapps)
Page 6) Silly Theories
Page 7) Conclusion
Silly Theories
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A dinosaur version of human AIDS, due to sexual promiscuity.
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Like Elvis, they aren't really dead but were abducted by aliens. Long live the King.
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Another alien related theory, is that the dinosaurs never existed, and that all the bones found were planted by aliens for a joke.
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The dinosaurs could not find a canyon deep enough for bungee jumping, which resulted in their ultimate death.
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The development of suicidal factors, perhaps in a similar way to lemmings, who are meant to commit mass suicide if overcrowded and stressed!
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One of the dinosaurs found a source of food now known to Humans as “Baked Beans”. One of the dinosaurs did an ‘Uber Fart’ and the stench was so bad that it wiped out the whole of its own race. That dinosaur died of constipation.
Extracted from: http://palaeo.gly.bris.ac.uk/Communication/Couch/Silly.html
Conclusion
I believe that dinosaurs became extinct by a super volcano because the evidence is stronger than all of the other theories. Also I think it is the most realistic of all the theories. The volcano would have erupted, killing all within a radius of a certain distance and the earthquake to follow would wipe out the entire race of dinosaurs. However, most scientists agree that the asteroid-impact hypothesis is supported by the most convincing collection of evidence.
This chart shows the amount of evidence scientists have found for each possible theory.