Earth gets a makeover

Mountains and volcanoes. The Late Cretaceous was a time of active plate movement, mountain-building, and volcanism. The Rocky Mountains, Andes, and Alps were all entering important growth periods.

India experienced a unique episode of volcanism that occurred between 65 and 60 Ma (from the very end of the Cretaceous into the Early Tertiary), consisting of episodes of lava flows, called the Deccan Traps, which spewed molten rock over an area of 500,000 km2. Volatile gasses - carbon dioxide, sulfur oxides, methane, and possibly nitric oxides among the most prevalent - were emitted into the atmosphere, possibly affecting global temperatures and damaging the ozone layer. Yet between the lava episodes over that 5 million year period, life apparently returned to normal.

Sea level. The Late Cretaceous was marked by lowered global sea levels (a regression), from highs enjoyed during mid-Cretaceous time (about 100 Ma). The regression peaked just before the K/T boundary and global sea levels began to rise as 65.5 Ma - currently our best date for the K/T boundary - came and went. Still, by the end of the Cretaceous, more land was exposed than had been in the previous 60 or so million years.

Seasons. We have seen that the latter half of the Cretaceous seems to have been a time of gentle cooling from the highs reached in the mid Cretaceous (see Chapters 2 and 13). In North America at least, climates through the Late Cretaceous were relatively equable, based upon plant fossils.

1. The extinction is thus said to have occurred at the Cretaceous-Tertiary (or K/T) boundary. The "T" in K/T obviously stands for the Tertiary Period. The "K" the German word Kreide, or chalk, because the Cretaceous was first identified at the chalk cliffs of Dover (England).

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