Cretaceous-Paleogene (K-Pg) Extinction Event (~66 Mya.)

A Cretaceous-Paleogene (K-Pg) Extinction Event (~66 Mya.) is an extinction event that marked the end of the Cretaceous period (an the Mesozoic era) and the beginning of the Cenozoic era (that continues today).

• AKA: K-T extinction event , K-Pg event.
• Context:
  • It can (often) be associated with the Chicxulub impact event, which is believed to have contributed significantly to the global environmental changes that led to this extinction.
  • It can be known for leading to the extinction of non-avian dinosaurs, among other species.
  • It can be preceded by a Cretaceous Thermal Maximum (~92 to ~66 MYA).
  • …
• Counter-Example(s):
  • A Triassic-Jurassic (Tr-J) Extinction Event (~182 Mya).
  • A Ordovician-Silurian Extinction Events, which are distinct as they were caused by drastic climate changes and not associated with an impact event.
  • A Holocene extinction, which is mainly driven by human activities, not a sudden global event.
  • An ongoing Anthropocene extinction, which is a result of human impact on the environment and not caused by a singular catastrophic event such as an asteroid impact.
  • …
• See: Extinction Event, Cretaceous Period, Paleogene Period, Mesozoic Era, Cenozoic Era, Chicxulub Impact Event, Dinosaur, Asteroid Impact, Impact Winter, Iridium Anomaly.

---

---

References

2017

• (Wikipedia, 2017) ⇒ https://en.wikipedia.org/wiki/Cretaceous–Paleogene_extinction_event Retrieved:2017-11-9.
  • The Cretaceous–Paleogene (K–Pg) extinction event,also known as the Cretaceous–Tertiary (K–T) extinction,was a mass extinction of some three-quarters of the plant and animal species on Earth that occurred over a geologically short period of time, approximately 65 million years ago. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that 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. As originally proposed in 1980 by a team of scientists led by Luis Alvarez and Walter Alvarez, it is now generally thought that the K–Pg extinction was caused by a massive comet or asteroid impact, estimated to be to wide, 66 million years ago and its catastrophic effects on the global environment, including a lingering impact winter that made it impossible for plants and plankton to carry out photosynthesis. The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the Chicxulub crater in the Gulf of Mexico in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred at the same time as the impact provides strong situational evidence that the K–Pg extinction was caused by the asteroid. Possibly, it was accelerated by the creation of the Deccan Traps, however, some scientists maintain the extinction was caused or exacerbated by other factors, such as volcanic eruptions, climate change, or sea level change, separately or together. A 2016 drilling project into the Chicxulub peak ring confirmed that the peak ring comprised granite ejected within minutes from deep in the earth (rather than usual seafloor rock), and evidence of colossal seawater movement directly afterwards (from layered sand deposits). Crucially the cores also showed a near complete absence of gypsum, the usual sea floor rock in the region, which is sulfate-containing; this would have been vaporized and dispersed as an aerosol into the atmosphere, providing evidence of a probable link between the impact and a global scale of longer-term effects on the climate and food chain. A wide range of species perished in the K–Pg extinction. The best-known victims are the non-avian dinosaurs. The extinction also destroyed a plethora of other terrestrial organisms, however, including certain mammals, pterosaurs, birds, lizards, insects, and plants. In the oceans, the K–Pg extinction killed off plesiosaurs and the giant marine lizards (Mosasauridae) and devastated fish, sharks, mollusks (especially ammonites, which became extinct), and many species of plankton. It is estimated that 75% or more of all species on Earth vanished. Yet the devastation caused by the extinction also provided evolutionary opportunities. In the wake of the extinction, many groups underwent remarkable adaptive radiations — a sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches resulting from the event. Mammals in particular diversified in the Paleogene, producing new forms such as horses, whales, bats, and primates. Birds, fish, and perhaps lizards also radiated.

---