How did the dinosaurs become extinct? What happened over 65 million years ago to kill a species that had survived for 150 million years? This is a question that has stumped scientists ever since dinosaur fossils were first discovered. Whatever caused the death of the dinosaurs also caused the death of about 70% of all of the species on the Earth. There are many theories as to how the dinosaurs became extinct. This page presents some of the most popular thoeries. Keep in mind that there is no absolutely proven theory. Noone knows for certain exactly why and how the dinosaurs became extinct...
Asteroids very seldom pass through the earth's atmosphere, but when they do they cause mass destruction. One of the most common extinction theories is that an asteroid 4-9 miles (10 km) wide struck the earth on the tip of the Yucatan Peninsula, in the Gulf of Mexico dealing the dinosaurs a fatal blow. Upon striking, the comet would have sent dust and steam into the atmosphere and caused huge forest fires, tidal waves, severe storms, and eliminated all sunlight. It would be six months before sunlight would reach the ground after such a blow. The dinosaurs, even in their prime, stood no chance without sunlight and plant life.
The climate of the Cretaceous period was tropical. Scientists know this because nearly one half of the plants in this time were tropical plants. Many scientists believe that at the end of the Cretaceous period the temperature dropped. If this drop in temperature is correct, many of the plants that the plant eating dinosaurs ate would die and thus many of the plant eaters would die as well. If the plant eaters died there would be nothing for the meat eaters to eat and they would eventually die out also. Plankton also seemed to decrease in number during the Tertiary period which could explain the death of the marine dinosaurs that fed on them. This popular theory just possibly could have caused the dinosaurs demise.
Could numerous volcanic eruptions have caused such mass destruction? Possibly. When volcanos erupt, they send huge clouds of dust, sulfuric acid, and poisonous gases into the air making the air almost impossible to breath. The dust and ash in the atmosphere would also change the climate and sunlight levels. On top of that, the ground would be covered with layers and layers of molten rock. The dinosaurs would never have survived such a hostile, poisoned environment!
Disease has also been proposed as the killer of the dinosaurs. As the Cretaceous period went on, more and more land bridges started to appear on the earth. The oceans started to dry up and the dinosaurs were able to walk across the land that was there. As the dinosaurs searched for food they would walk across these new land bridges and find relatives of theirs from when the lands of the world were one. But land bridges brought more than dinosaurs looking for food into the new land. They brought all of the diseases that those dinosaurs had inside of them. The diseases did not hurt those dinosaurs because they were immune to them, but to the other dinosaurs they could be fatal and the other way around. In most cases disease in a species is not fatal and is a positive thing because it will wipe out the weak so only the strong survive to pass their genes on to the next generation, but in the dinosaurs case it might not have been that way.
[The following theories are generally less accepted than the ones on the top.]
Stress on the dinosaurs is a possible solution for their extinction. This theory was first thought up by Heinrch K. Erben when he found that the shell thickness of a certain type of dinosaur species decreased as time went on. It was thought that the warm climate and good habitats in the Cretaceous period could have caused over population of dinosaurs, thus an increase of stress on the dinosaurs would develop. Stress is known to cause hormonal imbalances in modern day birds and lizards, so this could have happened to female dinosaurs. An increase of estrogen in the dinosaurs would have caused the females to lay eggs with shells too thin. If this happened it would greatly reduce the chances of the young to be hatched and live to adult hood.
Ozone Layer Depletion
The destruction of the earth's ozone layer is another proposal for the dinosaurs extinction. Hydrochloric acid from volcanic explosions (which are known to be numerous in the Cretaceous period) could have depleted the earth's ozone layer to a great extent. With the absence of this layer there would be nothing to protect the dinosaurs from the ultra violent rays of the sun. This could also explain why the dinosaurs and not the mammals seemed to die out because dinosaurs had no hair to protect them from the suns rays like the mammals of that time did.
The "greenhouse effect" is another possible solution to the dinosaurs demise. Massive volcanic eruptions could have released so much carbon dioxide into the atmosphere that it caused a drastic increase in the world wide temperature. Some deep sea drills have shown that the temperature of the ocean increased 65 million years ago so the temperature of the atmosphere also likely increased. The excess carbon dioxide from the eruptions in the atmosphere would have permitted the sun's heat into the earth's atmosphere, but would have blocked most of the heat from exiting the earth's surface back into space. This would have created a "greenhouse effect", the increase in temperature could have killed the tiny plankton responsible for converting most of the earth's carbon dioxide into oxygen which would further compound the problem. Only a few degrees increase in the temperature can affect the fertility of an animal by affecting their ability to produce fertile sperm.
Could a supernova have been responsible for the death of the dinosaurs? A supernova is an exploding star. It can blast material huge distances into space. Some scientists think cosmic radiation caused by the explosion would cause extremely high rates of deadly cancer among the dinosaurs. Others believe the radiation reacted with the Earth's atmosphere and destroyed the ozone layer. Without the ozone layer to filter out dangerous radiation, once again high rates of cancer could have occurred within the dinosaurs. Only small animals and plants, whose homes were sheltered from the harmful radiation would have survived.
Caterpillars which were believed to have evolved late in the Cretaceous period could have stripped plants of their leaves, a valuable food to the plant eating dinosaurs. If the caterpillars were able to strip all of the leaves from trees, then the plant eaters would not have anything to eat and would die. If the plant eaters died then the meat eaters would die from lack of food. Beware, this theory is thought to be extremely unlikely for caterpillars would have to strip all of the trees around the world of their leaves at virtually the same time.
The climate became too dry, making the environment too arid for the dinosaurs.
Multi-layer egg shells formed, with two or three shells on individual eggs, suffocating the embryos.
There is evidence that many of the large dinosaurs, must have had very small brains compared to their body size. With such small brain capacity responses to the surrounding environment would have been so slow that they could not compete with faster thinking animals.
Mass flooding destroyed important dinosaur habitats.
Dinosaur overpopulation could have resulted in severe competition and rivalry.
Mammals ate the dinosaur eggs preventing new generations surviving.
Carnivores over-killed their prey, and had nothing to eat.
Uranium leaked from the soil causing poisoning to the dinosaurs.
High levels of carbon dioxide destroyed the dinosaur embryos