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Earth’s early atmosphere contained only small amounts of free oxygen

The oxygen-rich atmosphere that evolved later, and upon which oxygen-breathing life now depends, was a result of the origin of photosynthesis.

During the Precambrian, vast numbers of single-celled algae and cyanobacteria living in the seas eventually released enough oxygen to transform the environment.

Table of Contents IntroductionThe Quaternary environmentGlaciationSea-level changesPaleoclimate

The most distinctive changes seen during the Quaternary were the advances of ice into temperate latitudes of the Northern Hemisphere.

The glacial landscapes were dominated by ice several kilometres thick that covered all but the highest peaks in the interior.

During the Late Cretaceous, the high levels of atmospheric carbon dioxide heated up the Earth in the same way as they do today.

The climate of the Triassic era was influenced by Pangaea, its centralized position stradling the equator, and the geologic activity associated with its breakup. Generally speaking, the continents were of high elevation compared to sea level, and the sea level did not change drastically during the period. Due to the low sea level, flooding of the continents to form shallow seas did not occur. Much of the inland area was isolated from the cooling and moist effects of the ocean. The result was a globally arid and dry climate, though regions near the coast most likely experienced seasonal monsoons. There were no polar ice caps, and the temperature gradient in the north-south direction is assumed to have been more gradual than present day. The sea level rose as the rift grew between North Africa and southern Europe, resulting in the flooding of Central and South Europe; the climates of terrestrial Europe were hot and dry, as in the Permian. Overall, it appears that the climate included both arid dune environments and moist river and lake habitats with gymnosperm forests.

rming on the Americas, North Africa was being split from Europe by the spreading rift. This division of the continents advanced further westward, eventually splitting eastern North America from North Africa.