Iridium anomaly/
Overview
The Iridium anomaly refers to an unusually high concentration of the chemical element iridium found in certain geological strata around the world. It is a significant piece of evidence supporting the Alvarez hypothesis, which posits that a large extraterrestrial body, such as a comet or asteroid, impacted Earth approximately 66 million years ago, leading to the Cretaceous–Paleogene (K–Pg) extinction event.
Iridium
Iridium is a dense, corrosion-resistant metal of the platinum group in the periodic table. It is one of the rarest elements in Earth's crust, with an average mass fraction of 0.001 ppm. However, it is found in significantly higher concentrations in certain types of meteorites, known as chondrites, and in the cosmic dust pervading space.
Discovery of the Iridium Anomaly
The iridium anomaly was first identified in the late 1970s by a team of researchers led by Nobel laureate Luis W. Alvarez. They discovered a layer of clay in the geologic record, now known as the K–Pg boundary, which contained iridium concentrations up to 20 times higher than normal. This layer corresponded to the time period of the mass extinction event that wiped out the dinosaurs and many other species.
Alvarez Hypothesis
The Alvarez team proposed that the iridium anomaly was the result of a massive asteroid or comet impact. The extraterrestrial body, rich in iridium, would have vaporized upon impact, spreading a layer of dust and debris, including iridium, around the globe. This hypothesis was initially met with skepticism, but further evidence, including the discovery of the Chicxulub crater in Mexico, has since lent it substantial support.
Evidence and Support
In addition to the iridium anomaly, several other lines of evidence support the impact hypothesis. These include shocked quartz and tektites, both of which are associated with high-energy events such as meteor impacts. Furthermore, the global distribution of the iridium layer suggests a rapid, catastrophic event.
Criticisms and Alternatives
Despite the compelling evidence, some scientists have proposed alternative explanations for the iridium anomaly. These include volcanic eruptions, nuclear explosions, and even the decay of a once-abundant, now-extinct iridium-rich organism. However, these theories struggle to account for all the available evidence and are generally considered less likely.
Impact on Science and Society
The discovery of the iridium anomaly and the development of the Alvarez hypothesis have had profound impacts on the fields of geology, paleontology, and astrobiology. They have also captured the public imagination, leading to widespread interest in asteroids, mass extinctions, and the history of life on Earth.