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Iridium is a chemical element; it has symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of 22.56 g/cm 3 (0.815 lb/cu in) [8] as defined by experimental X-ray crystallography. [a] 191 Ir and 193 Ir ...
The type locality of this iridium anomaly is near Raton, New Mexico. [1] [2]Iridium is a very rare element in the Earth's crust, but is found in anomalously high concentrations (around 100 times greater than normal) in a thin worldwide layer of clay marking the boundary between the Cretaceous and Paleogene periods, 66 million years ago.
The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, [a] is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the ...
Because of this, the Alvarez team suggested that an asteroid struck the Earth at the time of the K–Pg boundary. [12] There were earlier speculations on the possibility of an impact event, [188] but this was the first hard evidence, [12] and since then, studies have continued to demonstrate elevated iridium levels in association with the K-Pg ...
Alvarez hypothesis. The Alvarez hypothesis posits that the mass extinction of the non-avian dinosaurs and many other living things during the Cretaceous–Paleogene extinction event was caused by the impact of a large asteroid on the Earth. Prior to 2013, it was commonly cited as having happened about 65 million years ago, but Renne and ...
[5] [7] Iridium levels in this layer were as much as 160 times above the background level. [8] It was hypothesized that the iridium was spread into the atmosphere when the impactor was vaporized and settled across Earth's surface among other material thrown up by the impact, producing the layer of iridium-enriched clay. [9]
Iridium is extremely rare in the Earth's crust, but it is very abundant in most asteroids and comets, as asteroids have a concentration of iridium of about 455 parts per billion while the Earth's crust typically contain only about 0.3 parts per billion. They interpreted it as debris from an impact that deposited around the globe.
Earth's surface is very depleted in iridium, which primarily resides in Earth's core. The only significant source of the element at the surface is cosmic particles that reach Earth. During a snowball Earth, iridium would accumulate on the ice sheets, and when the ice melted the resulting layer of sediment would be rich in iridium.