User:Abyssal/Prehistory of Antarctica

The Cretaceous–Paleogene extinction event was the mass extinction of three-quarters of Earth's plant and animal species during a geologically brief interval about 66 million years (Ma) ago. A wide range of species perished in the K–Pg extinction, most notably the non-avian dinosaurs. However, other groups that sustained losses or vanished include mammals, pterosaurs, birds, lizards, insects, and plants. In the oceans, the K–Pg extinction devastated the giant marine lizards, plesiosaurs, fishes, ammonites and plankton. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era which continues today.

In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth's crust but abundant in asteroids. It is now generally believed that the K–Pg extinction was triggered by a massive comet/asteroid impact and its catastrophic effects on the global environment, including a lingering impact winter that halted photosynthesis in plants and plankton. However, some scientists maintain the extinction was caused or exacerbated by other factors, such as volcanic eruptions, climate change, and/or sea level change. Whatever the cause, many of the surviving animal groups diversified during the ensuing Paleogene period. Mammals in particular radiated into new forms such as horses, whales, bats, and primates. (see more...)

The history of paleontology traces the history of the effort to study the fossil record left behind by ancient life forms. Although fossils had been studied by scholars since ancient times, the nature of fossils and their relationship to life in the past became better understood during the 17th and 18th centuries. At the end of the 18th century the work of Georges Cuvier ended a long running debate about the reality of extinction and led to the emergence of paleontology as a scientific discipline.

The first half of the 19th century saw paleontological activity become increasingly well organized. This contributed to a rapid increase in knowledge about the history of life on Earth, and progress towards definition of the geologic time scale. As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. After Charles Darwin published Origin of Species in 1859, much of the focus of paleontology shifted to understanding evolutionary paths.

The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America. The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection, as demonstrated by a series of important discoveries in China near the end of the 20th century. There was also a renewed interest in the Cambrian explosion that saw the development of the body plans of most animal phyla. (see more...)

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