02. Why did the dinosaurs die out?
What was the climate like during the Mesozoic Era (250- 65 million years ago)?
When dinosaurs ruled the Earth, the climate was most likely hot and humid. There is no evidence of Ice Ages or glaciations found in rocks of this age. There is a lot of evidence of tropical species existing at this time. Atmospheric carbon dioxide was close to present-day levels. The ice caps at the North and South Pole had melted, resulting in raised sea levels. Australia was breaking away from Antarctica and gradually moving away from the South Pole, closer to the Equator.
Conifers and ferns dominated the landscape and the first flowering plants were appearing. About half of Australia was covered by shallow inland seas. Evidence for this comes from fossils found in the rocks of this region. They contain marine molluscs and large pre-historic reptiles such as ichthyosaurs and plesiosaurs. Today this area is called the Great Artesian Basin.
Further information on the great inland seas of the Cretaceous period can be found at the following link.
What happened to the climate during the Cretaceous period?
Between the early to mid-Cretaceous, the world climate became warmer by as much as 10°C. Some scientists have linked this stage of global warming to a huge asteroid impact. Others have linked it to the large number of volcanic eruptions in the area that today is India and Pakistan.
The Late Cretaceous Period was a time of great change. The continents were breaking up. Volcanoes were throwing ash and gas into the atmosphere, rapidly altering the climate.
Sea levels fell in the final stage of the Cretaceous. Changes in climate would have occurred due to the disruption of wind and ocean currents. These marine changes, combined with volcanism and an extraterrestrial impact, may have caused the mass extinctions.
Artist’s impression of climate change during the Cretaceous. Artist: J.T. Bauer, © Queensland Museum.
SUDDEN OR GRADUAL CHANGE?
Was the extinction of the dinosaurs due to a sudden change or a gradual change?
Perhaps a dramatic change interrupted the weather patterns or destroyed the food of the dinosaurs. Factors that could cause a sudden change would be an asteroid, meteorite or comet.
Species become extinct if there are no individuals in the population with the necessary characteristics to survive in the changed environment. This is what happened to the dinosaurs and many other species that became extinct at this time.
Other changes may have occurred over a longer time period. Perhaps the warm, wet climate gradually changed to a drier, cooler one. In many areas, the fossil record shows tropical vegetation was replaced by woodland plants. Once again, it is possible that the dinosaurs were not adapted to the new environment and therefore became extinct.