PPT07 - Mesozoic Climate Change

PPT07 - Mesozoic Climate Change - Mesozoic climate was...

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Mesozoic climate was generally warm worldwide… In previous lectures, we have seen that during the Mesozoic, i.e. that period of time between 251Ma and 65Ma ago dominated by dinosaurs, climate was generally warm worldwide. Although climate did stay warm (compared to today) during that period, it evolved slowly from dryer and strongly seasonal conditions during the Triassic towards increasingly warmer, wetter and more equable conditions through the Jurassic and Cretaceous TRIASSIC Dinosaurs appeared during the mid-Triassic Fauna dominated by other reptiles and amphibians The main reason for this gradual change in climate is the gradual changes in continental configuration during that period During the Triassic, all continents that we recognize today were glued together in one big land mass called Pangaea (Note that the map above outline the position of today’s landmasses, such as North America, Greenland and Eurasia in the northern hemisphere; South America, Africa, India, Antarctica and Australia in the southern hemisphere) There was also only one big ocean, called Panthalassa, with the Tethys Sea intruding into the continent at low latitude, straddling the equator The dinosaurs did not appear at the start of the Mesozoic, but rather mid-way through the Triassic, some 225 Ma ago The Late Triassic was still dominated by other reptiles and large amphibians, while dinosaurs were still comparatively small and rare. Mammals also first appeared during the Late Triassic Many of these reptilians and amphibians species that dominated the world at that time became extinct by the end of the Triassic, freeing ecological niches and allowing dinosaurs to diversify. Warm climate - No polar ice caps - Monsoons Climate at that time was already warm There were no polar ice caps during the Triassic climate was much warmer than today and less varied with latitude (that was the case throughout the dinosaur age) Climate was strongly seasonal and dominated by monsoons There were two very distinct seasons; one wet (summer) and one dry (winter)
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Summer: Land masses warmer than surrounding oceans air rises over land (low pressure) humid oceanic air flows towards land rises and cools rainy summers Winter: Land masses cooler than surrounding oceans air sinks towards land (high pressure) dry continental air flows from land dry winters What produces monsoons? During summer, land masses become warmer than the surrounding oceans warmer air rises over land (low barometric pressure) this creates a flow of air from the ocean towards land to replace the rising air. As the wet air rises above land, it cools. Water vapor condenses to produce rain During winter, land masses become cooler than the surrounding oceans colder air sinks towards land (high barometric pressure) this creates a flow of air from land towards the ocean as air now rises above the ocean. This prevents wet moisture-laden oceanic air to reach land
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PPT07 - Mesozoic Climate Change - Mesozoic climate was...

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