Environment Magazine

Climate in Mesozoic Era.

Posted on the 31 December 2019 by Priyadarshi @priyadarshi64

The Earth was hotter than it is today.

ByDr. Nitish PriyadarshiGeologist.Email: [email protected]


In recent years, the scenario of future global environment is haunting the man as the present environmental changes (e.g. global warming) pose considerable danger to his own existence and environment. He is presently struggling to understand as to what will be the nature and extent of these changes in the next hundred years. In order to understand the processes of changes and the effects they are likely to have on the future environment of the biosphere, we should develop a historical perspective- a perspective based on global environmental changes preserved in the rocks of the planet earth.
The history of earth’s climate is characterized by change. Times of glaciation on the earth have been followed by warm intervals and the duration in years of both cold and warm intervals has varied by several orders of magnitude.
Climate change is changing the world. Either it is in the form of temperature rise or in the form of severe floods. Many times question arises in my mind whether this climate change is the outcome of present human activities on the earth or it has happened in early geological ages too. Answer is “yes” climate change has occurred several times from the beginning of the earth formation. Evidences are preserved in from of rocks, sediments, and fossils. Studying the records of past climate change will fill you like reading thriller novel in which every chapter is full of suspense and thrill. Every chapter of this novel denotes different geological periods with different stories of climate change. Change is the only constant in the history of the earth. Since its creation around four billion years ago, our home planet has constantly been subjected to changes brought about by the interplay of internal of forces and external influences. The enormous lithospheric plates are continually shifting, reshaping the continents. Volcanic eruptions and earthquakes are the visible results of this process. Seen from the perspective of the history of the earth, our planet, as we know it today, is merely a snapshot in time. Everything is in a state of flux. Everything- including the climate- is locked in a continuous process of change, giving rise to favourable and unfavourable conditions to which all life on earth-human, plant and animal- must constantly adopt.
My article is about the climate conditions of the Mesozoic.
The term “Mesozoic” was introduced by John Phillips in 1840 for the rock formations containing remains of “middle forms” of life. The Mesozoic Era that began at about 230 million years ago and closed at about 65 million years ago represents less than half the duration of the Palaeozoic Era. The Mesozoic Era has been further subdivided into Triassic, Jurassic and Cretaceous periods. The lower boundary of the Mesozoic is set by the Permian–Triassic extinction event, during which approximately 90% to 96% of marine species and 70% of terrestrial vertebrates became extinct. It is also known as the "Great Dying" because it is considered the largest mass extinction in the Earth's history. The upper boundary of the Mesozoic is set at the Cretaceous–Paleogene extinction event (or K–Pg extinction event), which may have been caused by an asteroid impactor that created Chicxulub Crater on the Yucatán Peninsula. Towards the Late Cretaceous, large volcanic eruptions are also believed to have contributed to the Cretaceous–Paleogene extinction event. Approximately 50% of all genera became extinct, including all of the non-avian dinosaurs.
Pangaea was characterized by extreme climate variations because it was such a huge continent. The coastal areas near Equator had a monsoon climate with summer rain, while its interior areas were dry and desert-like. Pangaea was a many times larger continent than Eurasia, most likely with an even more pronounced continental climate. One cannot doubt that winters in central Pangaea must have been very harsh experiences, and summers must have been insufferable glowing hot. There were no actual ice ages during Mesozoic. Pangaea was the largest continent ever, and it was surrounded by an equally huge ocean that was the Panthalassic Sea, which covered the rest of Earth's surface. It is believed that the shores of Pangaea must have been exposed to very strong monsoon winds.
Three of the five largest mass extinctions in Earth history are associated with the Mesozoic: a mass extinction occurred at the boundary between the Mesozoic and the preceding Paleozoic; another occurred within the Mesozoic at the end of the Triassic Period; and a third occurred at the boundary between the Mesozoic and subsequent Cenozoic, resulting in the demise of the dinosaurs.Perhaps the largest number of palaeogeographic reconstructions have been made for the Mesozoic Era. In many parts of the world, the Era began with a new phase of sedimentation . Pangaea, the supercontinent of the Palaeozoic Era was gradually torn apart during the Mesozoic Era. Fragmentation of the Pangaea began with the opening of proto-Atlantic and proto-Indian oceans. On the basis of the palaeo-magnetic evidence, it has been suggested that that this break- up began with the separation of North America and Gondwana Land in  Late Triassic Epoch.  The Mesozoic was a time of significant tectonic, climate, and evolutionary activity.  

The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. We can also say that “Earth’s climate during the Mesozoic Era was generally warm, and there was less difference in temperature between equatorial and polar latitudes than there is today”.   The Mesozoic is characterized by a warm and humid Earth. Oxygen levels were very similar to today’s levels, thanks to the large coniferous forests that proliferated in the early Triassic period but were replaced by Angiospermae forests in the early Cretaceous.We pass from a dry and arid climate at the beginning of the Triassic as we leave an extinction that left the continents dry, to still warm climates but with greater humidity at the beginning of the Jurassic and remain so until the end of the Cretaceous. It is thought that in the Cretaceous, the North Pole was able to hold ice in winter.

Dinosaurs first appeared in the Mid-Triassic, and became the dominant terrestrial vertebrates in the Late Triassic or Early Jurassic, occupying this position for about 150 or 135 million years until their demise at the end of the Cretaceous. Birds first appeared in the Jurassic (however, true toothless birds appeared first in the Cretaceous), having evolved from a branch of Theropod dinosaurs.Pangaea began breaking up at the end of the Triassic. Between North America and Africa, volcanoes were spewing out large amounts of alkaline lava, which can be found on both continents. It is assumed that this volcano disaster initiated another round of extinction of up to 80% of Earth's species, and thus paved the way for the dinosaurs that came to dominate the Earth in the next hundred million years. Some believe that the root cause of species extinction was that the intense volcanic activity volcanoes emitted so much CO2 that the Earth's temperature rose dramatically so that the heat was the real killer that wiped out so many species.
Jurassic began 213 million years ago and lasted until 144 million years before present, a total of 69 million years. The gradual break-up of Pangaea that began in the late Triassic, continued in Jurassic. The climate of the new and smaller continents was milder and more rainy. Hot and humid tropical breezes blew through dense forests of ferns, cycads, ginkgo trees and various conifers.
Since large parts of the Earth's surface were covered by water and green plants, planet's albedo decreased, and more of the Sun's energy was absorbed as heat. The increased atmospheric moisture content also helped to increase the temperature, because water vapor is a greenhouse gas.There is strong evidence that the sea surface level in the World increased during the Jurassic, which meant that many low-lying areas were transformed into shallow coastal sea, and in the same time the climate became more oceanic, that is wetter, warmer and with much less seasonal variation.The Cretaceous period began 145 million years ago and lasted until the dinosaur extinction 65 million years ago. During this period prevailed almost everywhere on Earth a warm and humid climate. The thick layer of chalk, which was created by the microscopic calcareous algae that have been found in abundance throughout the Earth's oceans, gave its name to the period. Up until then, chalk deposits had been restricted to shallow coastal waters.
By the middle of the Cretaceous period about 100 million years ago, the mean- temperature on the planet's surface was between 6 and 12 degrees higher than it is today. The annual mean temperature in the Arctic was about 10 degrees, which is about 20 degrees warmer than today. In the tropical regions, the surface water temperature was approx. 5 to 10 degrees higher than the present.The environment was unusually warm and polar ice caps did not yet exist. This played a large part in evolution and is a key factor behind the flourishing of the dinosaurs. During the Triassic period the climate was generally dry, which changed near the Jurassic period as oceans began to rise due to mounting layers of magma covering the seafloor. As a result, flooding overtook many parts of the exposed land. This allowed the climate to change with increased humidity and it continued that way even into the Cretaceous period. However, the climate began to cool during the Cretaceous although temperatures may have risen again near the end of the Mesozoic.Understanding how the Earth responded to past extreme warming and CO2 input can help us prepare for how the planet will respond to current, human-caused climate change.
K. Ravindra, 1988. Fundamentals of historical geology and stratigraphy of India. Wiley eastern limited, New Delhi.https://www.britannica.com/science/Mesozoic-Erahttp://www.dandebat.dk/eng-klima3.htmhttp://nitishpriyadarshi.blogspot.com/2012/09/climate-which-changed-world-56-million.htmlhttps://nitishpriyadarshi.blogspot.com/2007/12/climate-change-is-not-recent-phenomenon.html

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