Iridium anomaly

As an iridium anomaly is called the world's detectable increased concentration of the element iridium and other platinum metals in rocks from sediments that were 65 million years ago, at the Cretaceous - Tertiary boundary, deposited.

Background

The platinum metal iridium usually occurs only at very low concentrations of about 0.4 ppb in the Earth's crust. 50 ppb observed - in rocks from the Cretaceous-Tertiary boundary, most commonly in karbonatarmen mudstones, iridium concentrations were 0.5 world. This partial extremely high concentrations that exceed the average significantly, could be out for Iridium demonstrated for the other five platinum metals ruthenium, rhodium, palladium, platinum and osmium. Of these metals, iridium is the easiest to demonstrate by neutron activation; the increased concentrations of the other elements were only discovered when the term iridium anomaly was coined.

Discovery

Was scientifically described the global anomaly occurring in 1980 by Nobel laureate Luis Walter Alvarez, his geologist son Walter Alvarez and Frank Asaro and Helen chemists Michels in rocks from Gubbio in Italy and Stevnsfortress Klint in Denmark. The Italian samples contained an approximately 30 times higher iridium content than normal, the proportion in the Danish samples exceeded the normal concentration even at the 160 -fold. Since such high iridium concentrations up to 550 ppb are only known from meteorites, the scientists concluded on an enrichment of the element by a massive impact event, the impact of a colossal meteorite. The distribution was carried out by global atmospheric transport of high whirled iridium-containing dust. The trigger for the iridium anomaly applies the Cretaceous-Tertiary impact, whose testimony is the Chicxulub crater in the north of the Yucatán Peninsula in the Gulf of Mexico today.

Earthly cause and counter-arguments

Critics see the impact theory is not the only possible cause, because platinum metals can also be enriched by volcanic activity. In contrast, however, the detectable anywhere on earth unusual iridium isotope ratios speak in the sedimentary rocks. The impact theory is supported further by the chromium isotopic ratios that occur in the same layers and largely correspond to those in chondritic meteorites ( stony meteorites ).

Today it is well established that the iridium anomaly was caused by the impact of a celestial body.