Change in Climate of Earth and Challenges faced by Dinosaurs
The Earth probably came into existence about 4 – 6 billion years ago. It is presumed that life originated on Earth about millions of years ago and since then innumerable varieties of living beings have evolved. The original temperature of earth is estimated to be around 5,000-6,000 c. There was well formed atmosphere at that time, but it did not contain free Oxygen. With the cooling of the Earth, free atoms in the atmosphere came together and formed inorganic molecules. Further evolution resulted in the diverse forms of existing organisms. The history of evolution of life on Earth is constructed by the study of fossil plants and animals from various strata of the Earth. The most abundant fossils are formed by petrifaction in which hard parts like bones, teeth and exoskeleton of organisms were preserved in the rock strata. By studying different types of fossils in different rock strata and determining their age, geologists have constructed a geological time scale which is the calendar of Earth’s past history.
Mezozoic Era is the “Age of Dinosaurs”. This Era began about 251 million years ago and ended about 65 million years ago. It is divided into three periods: Triassic (251 to 199 Ma), Jurassic (199 to 147 Ma) and Cretaceous (147 to 65 Ma). Reptiles evolved in this era and became rulers of the Earth. They occupied land (Dinosaurs), sea (Ichthyosaurs) and air (Pterosaurs). Dinosaurs evolved in Triassic period and spread during the Jurassic period. However they dominated Cretaceous period. Since then there has been a great transition in the climate and atmosphere of Earth.
Comparison of Climate, Flora and Fauna of Earth today and 65 million years ago (Late Cretaceous period)
Cretaceous period was marked with the growth and spread of Angiosperms (flowering plants). They had dense leaves, stems and branches. Plants like magnolias, roses, willows and redwood trees were found in large numbers. Even grass, oak, maple, grape, el also came into existence.
Due to large number of flowering plants, this period also saw the presence of insects similar to today’s insects. Termites and ants appeared in the late Cretaceous period. Evolution of aquatic organisms is also observed. Crabs, lobsters, sea urchins, foraminifers, nautiluses are some of the marine invertebrates which were found in the Cretaceous period. Appearance of modern sharks was also seen. Recently, it has been found out that Myledaphus bipartitus (a guitar fish) was also present 75Ma (Wilson and Newbrey et al., 2013). Diversification of birds was also seen in this period. However, reptiles dominated the Earth 65 million years ago and this period was marked with large numbers of dinosaurs. Reptiles reached their zenith, including the dinosaurs Triceratops, Tyrannosaurus, Stegosaurus, Apatosaurus (Brontosaurus), and Iguanodon, and ranged from herbivores to carnivores. The flying retiles like pterosaurs and aquatic ichthyosaurs, plesiosaurs were also developed. Even the reptiles like snakes, lizards, crocodiles appeared (Infoplease.com, 2013). However, mammals were small and rare.
During the start of Mezozoic Era, temperature was warm and dry. Before appearance of Dinosaurs, temperature was around 10-15C and the climate had become warmer by the end of Triassic period. During the beginning of Cretaceous period, Pangea had already drifted apart and it had also split into many continents. About 65 million years ago, near the end of Mezozoic era, North America separated from Europe. This generated new coastline, growing of seasons and thus cooling of global climate took place. Thus during the end of Cretaceous period, lowering of temperature was seen. Thus dinosaurs also had to suffer from climate change.
The temperature of Cretaceous period was warmer than today although there was a cooling trend (Hallam A.J., 1985). The mean temperature during Cretaceous period is estimated to be around 21 degree Celsius which is 6C higher than current mean temperature (15C) (Ncdc.noaa.gov, 2013). There was higher concentration of greenhouse gases like carbon dioxide in the Cretaceous period (Sellwood and Price et al., 1994). Mammals have evolved to more complex human beings today as compared to Cretaceous period where there we very less and small mammals. One of the major reasons of extinction of dinosaurs is abrupt cooling of temperature (abrupt climate change). Earth is facing abrupt climate change now also which is one of the reasons for non-existence of dinosaurs today.
Challenges faced by dinosaurs
Apart from abrupt changes in temperature, there are some other reasons which might account for non-existence of non-avian dinosaurs today. An animal like dinosaurs requires large amount of Oxygen to carry out its metabolism due to its large body size. But the concentration of Oxygen has decreased now which might be a hindrance in its survival. Also due to deforestation, there is lack of habitat and prey.
Based on past climate patterns it is be likely that Earth’s climate would be directed back into an Ice Age within the next few thousand years. But current data shows that much of the climate system is in fact heating up due to global warming. Some recent evidences also suggest that dinosaur’s were warm blooded and had survived in a warmer climate than today but the abrupt climatic and geographical changes suggest for the non-existence of non-avian dinosaurs.
Hallam, A. J. geol. Soc. Lond. 142, 433−445 (1985).
Infoplease.com (2013). Cretaceous period: Evolution of Plant and Animal Life |
Infoplease.com. [online] Retrieved from: http://www.infoplease.com/encyclopedia/science/cretaceous-period-evolution-plant-animal-life.html [Accessed: 16 Sep 2013].
Ncdc.noaa.gov (2013). Future Forecasts. [online] Retrieved from:
http://www.ncdc.noaa.gov/paleo/ctl/future1.html [Accessed: 16 Sep 2013].
Sellwood, B., Price, G. and Valdest, P. (1994). Cooler estimates of Cretaceous temperatures.
Nature Publishing Group. 370, 453 – 455
Wilson, A., Newbrey, M., Brinkman, D., Cook, T. and Neuman, A. (2013). Age and growth
in Myledaphus bipartitus, a Late Cretaceous freshwater guitarfish from Alberta, Canada. Canadian Journal of Earth Sciences, 50(9): 930-944, 10.