Cretaceous–Paleogene boundary

The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band. It defines the end of the Mesozoic Era, and is usually estimated at around 66 Ma (million years ago), with more specific radioisotope dating yielding an age of 66.043 ± 0.011 Ma.K is the traditional abbreviation for the Cretaceous Period, and Pg is the abbreviation for the Paleogene Period. The boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period of the Cenozoic Era. The boundary is associated with the Cretaceous–Paleogene extinction event, a mass extinction which is considered to be the demise of the non-avian dinosaurs in addition to a majority of the world's Mesozoic species.

Possible causes

Alvarez impact hypothesis

In 1980, a team of researchers consisting of Nobel prize-winning physicist Luis Alvarez, his son, geologist Walter Alvarez, and chemists Frank Asaro and Helen Michel discovered that sedimentary layers found all over the world at the K–T boundary contain a concentration of iridium many times greater than normal (30 times the average crustal content in Italy and 160 times at Stevns on the Danish island of Zealand). Iridium is extremely rare in the earth's crust because it is a siderophile element, and therefore most of it sank with iron into the earth's core during planetary differentiation. As iridium remains abundant in most asteroids and comets, the Alvarez team suggested that an asteroid struck the earth at the time of the K–T boundary. There were other earlier speculations on the possibility of an impact event, but no evidence had been uncovered at that time.

Kät

Kät may refer to:

KT

KT, kT or kt may refer to:

Arts and entertainment

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List of Caribbean membranophones

This is a list of membranophones used in the Caribbean music area, including the islands of the Caribbean Sea, as well as the musics of Guyana, Suriname, French Guiana, Belize, Garifuna music, and Bermuda. It only includes membranophones that are indigenous to the local music area or are a vital and long-standing part of local culture. It does not include membranophones that are, for example, a part of Western style orchestras, nor does it include trap sets and other common membranophones used in popular music recordings of many genres across the world. Almost all membranophones are drums and percussion instruments.

The Hornbostel-Sachs number is given after each instrument.

References