The Element Iridium
as Evidence of
Catastrophic Impacts Resulting in Major Extinctions

Iridium, an element belonging to Platinum Group of Precious Metals, is very rare in earth's crustal rocks but is present in higher concentrations in meteorites.
Meteorite impacts on Earth have been linked to the discovery of abnormally high concentrations of Iridium in rock layers belonging to specific geologic time periods.
These time periods, where the presence of Iridium in crustal rocks spikes, coincide with major extinctions of plant and animal life on Earth.
Consequently, Iridium anomalies, along with other impact evidence such as shocked quartz and tektites, have led some scientists to conclude that meteorite impacts were directly related to major earth extinctions.

A meteorite impact would have devastating effects on life. As the meteor passes through Earth's atmosphere, frictional heat upon entry would incinerate objects on Earth's surface causing wildfires and the immediate death and destruction of about 25% of all biomass. The actual impact would result in major earthquake tremors, followed by tsunamis, changes in sea level, massive volcanic eruptions, high winds and acid rainfall, the latter of which would not only affect life on land but also cause fish kill in marine environments. Volcanic eruptions may even occur on the opposite side of the Earth from where the actual impact occurred. Such eruptions are believed to have taken place when an asteroid formed the the K-T impact crater and there was simultaneous volcanism, known as the Deccan Traps, where India is today. All of these catastrophic events would have far reaching, global effects. Material ejected from the actual impact site (dust, ash, debris) would rise through the troposphere and into the stratosphere, blocking sunlight for months. Global temperatures would fall and Earth would be in a state similar to a Nuclear Winter. Earth's oxygen levels would significantly decrease as well.

The absence of sunlight would initiate a chain of events ultimately ending in global mass extinction for any life that survived the initial impact. Photosynthesizing phytoplankton and land plants are the first to succumb to the absence of sunlight. Herbivores, dependent upon plants, would die, followed by the carnivores. This chain of events is inevitable since plant life exists at the bottom of the food chain with many other life forms dependent upon plants for survival. Any species unable to adapt to these sudden changes in their environment would die out. Mass dying would occur on land and also in the oceans where many marine species are dependent upon phytoplankton for their existence.

When the polluting dust from the impact finally settled out of Earth's atmosphere, global warming would then begin. A Greenhouse Effect, caused by the increased presence of Carbon Dioxide and Nitrous Oxides, along with less UV blocking Ozone in the stratosphere, would lead to rising global temperatures. Clearly, all these scenarios make the struggle for survival almost insurmountable with large percentages of life disappearing forever and only a few life forms remaining to repopulate Earth. Over time these survivors would adapt to changing environments and evolve into new and different species.

Three extinction events have been linked to extraterrestrial impacts based on the presence of Iridium in rock layers:

The great Dinosaur Extinction, dated at 65 mya, commonly referred to as the Cretaceous-Tertiary (K-T) Extinction.

High Iridium concentration.
Crater Evidence.
Impact Theory is widely accepted though not necessarily as the single cause for extinction.
Debated by some scientists who are intrinsic gradualists rather than catastrophists.

The Permian Extinction which occurred approximately 245 mya.

Crater Evidence.
Very limited Iridium presence.
Disputed theory.

The Triassic-Jurassic Extinction which occurred approximately 200 mya.

High Iridium concentration.
No impact crater has yet been discovered.

Cretaceous Tertiary Extinction

In 1980 physicist Luis Alvarez along with his son, geologist Walter Alvarez, both of the University of California, developed the Alvarez Asteroid Impact Theory as an explanation for the extinction approximately 50% of all life, including the dinosaurs, that occurred approximately 65 million years ago. In Italy, high levels of Iridium were found in sedimentary rocks at the boundary between Cretaceous and Tertiary rock layers. The rocks were chemically dated to be around 65 million years old and this coincided with the K-T mass extinction. High concentration of Iridium, coming from meteorites that have impacted Earth, would eventually settle as a layer of "dust" on Earth's crust, be covered over time with additional sediment and lithified rock layers, preserving the record of impact in the geologic record. Similar Iridium layers, 1-2 cm thick, located at the K-T boundary, have been identified at other locations around the globe.

The "Alvarez asteroid", estimated to have been 4-9 miles in diameter, impacted the earth at an angle of approximately 20 to 30 degrees from the horizontal, forcing scalding hot debris to the northwest, causing a chain of globally catastrophic events as described in the Iridium section above. In 1991 scientists found evidence of what is believed to be the impact crater that caused this extinction event near the tip of the Yucatán Peninsula in the Gulf of Mexico. The crater, Chicxulub, is 120 miles wide and 1 mile deep.

However, "...Princeton paleontologist Gerta Keller contends that multiple impacts contributed to a prolonged extinction over several hundred thousand years."¹ This statement may be supported by additional discoveries. The Shiva crater, evidence of another huge impact event, also chemically dated to have formed approximately 65 million years ago, was found under the Arabian Sea off the coast of India near Bombay. Though somewhat destroyed by millions of years of seafloor shifting, when scientists "piece" evidence together, the crater would be about 370 miles by 280 miles across and 7.5 miles deep.
In North America alone there is evidence of a reduction in the number of dinosaur species over the millions of years preceding the Yucatán Peninsula and Shiva impact craters. Perhaps, the K-T impact events were the final blow to an already dying breed.

Whether the cause of mass extinction was Iridium-bearing meteorites or a combination of impacts and other factors, there is no doubt that the K-T boundary marks a major extinction event with the disappearance of 90 percent of known types of leaf-bearing trees and plants and up to 70 percent of all species, including all non-avian dinosaurs. Ironically, the carcasses of the deceased animals may have provided smaller, burrowing animals with enough food to last them for quite awhile. Many smaller mammals that coexisted with dinosaurs were able to survive the meteorite's devastating effects, repopulating and evolving into larger and more diverse species.

Permian Extinction

The largest mass extinction event occurred around 250 million years ago, when about 95 of all species went extinct, over 90% of marine and 70% of vertebrate land species. In April 2000, a 125 mile wide crater, called Bedout, was found buried off the northwestern coast of Australia. The crater, which would have been formed by a 10 kilometer wide asteroid, was dated at approximately 250.7 million years old and coincides with the "Great Dying" that occurred at the end of the Permian Period. In the area of the Bedout crater, Kevin Pope of Geo Eco Arc Research found shocked quartz, the same type associated with a meteorite impact. "In 1997, University of Oregon paleontologist Gregory Retallack reported finding elevated Iridium levels and shocked quartz crystals in Permian-Triassic rocks telltale signs of an impact".² Retallack also maintains that a major impact could have caused not only the increased volcanism many scientists hold as the cause for Permian extinctions, but also a polluting of Earth's oceans by the release of methane which would have depleted water of life-sustaining oxygen, thereby causing the high percentage of marine deaths at that time.

At present, there is only limited and disputed evidence of Iridium and shocked quartz occurring with the Permian impact event. Therefore, many scientists still attribute the Permian extinctions to major volcanism occurring around Siberia which lasted hundreds of thousands of years, an eruption which would have resulted in major climatic changes. Iridium amounts found in the area of the Australian Bedout crater were very small compared to those associated with the asteroid impact that formed the crater believed responsible for the K-T extinctions. There simply are no obvious Iridium spikes to support a major impact event as the sole cause of the Permian die-offs. Meteor impacts, large-scale volcanic eruptions, drastic changes in sea level, and severe climate changes have all been linked at one time or another to the Permian extinctions and, in fact, the mass dying may have been caused by a combination of occurrences.

Triassic-Jurassic Extinction

Approximately 200 million years ago, at the end of the Triassic period and the beginning of the Jurassic, an extinction event took place that obliterated about 23% of all marine families, most archosaurs, therapsids, the last of the large amphibians and reptiles and 42% of terrestrial tetrapod families. Strong evidence exists that a major impact event may have occurred that devastated the fauna and flora of North America, causing 60-80% of all plant and animal species to become extinct, while at the same time allowing all major groups of terrestrial vertebrates to evolve as well as the ascent of the Jurassic dinosaurs as the dominant species on Earth, a position they held, without challenge, for around 143 million years.

Less than 10,000 years after the Triassic-Jurassic boundary, large theropod dinosaurs appeared, as evidenced in fossilized skeletal remains found in over 70 locations in North America. Plant eating dinosaurs dwindled in numbers while carnivorous species became more abundant. Dinosaur diversity peaked 100,000 years after the Triassic-Jurassic boundary and dinosaurs continued to dominate for another 135,000 years.

The presence of Iridium spikes (an anomaly up to 285 parts per trillion; average maximum up to 141 ppt) at several locations in North America provides evidence that an impact possibly occurred at the Triassic-Jurassic time juncture. However, no impact crater has yet been found.
"As reported by Olsen, et. Al. in the May 17, 2002 issue of Science, levels of the metal Iridium that rarely occurs naturally on the Earth's surface and mostly arrives on extraterrestrial objects, has a prominent peak in rocks from the time when many species died out at the Triassic-Jurassic boundary."³

That dinosaurs could have survived a catastrophic meteor impact may be attributed to the fact that warm-bloodedness gave them an advantage in a climate that changed quickly from a stable one, to a much colder climate, then to a much warmer one. Also, scavenging various types of food would give them an advantage. Such were characteristics of the dinosaurs.

P.E. Olsen's impact theory as to the cause of the Triassic-Jurassic extinctions is not without challenge. Other scientists have different theories why the Triassic-Jurassic extinctions occurred including: concurrent Volcanic Flood Basalts resulting in a Greenhouse Gas Climate Effect (McElwain, 1999; Hesselbo, 2002) as well as sea level changes which would change existing habitats on a global scale (Hallam 1990).

Debunking Olsen's research (1987) and theories concerning a sudden supremacy of dinosauria, T. Thulborn states "...the emergence of big predatory dinosaurs was not the consequence of mass extinction at the Triassic-Jurassic boundary, and the footprint assemblages of the Newark Supergroup likely reflect local (Laurasian) events in dinosaurian history, rather than events of global significance."⁴ Consult Thulborn's article for specific details supporting his comment.

To summarize, scientists will continue to look for evidence of high-level Iridium concentrations in rock layers to support "Impact Extinction Theories". For there is no doubt that Iridium is a valid marker for a possible extraterrestrial event. When discovered and when theories are proposed, they will continue to be challenged, debated and countered with alternate possibilities. No doubt, in the past, meteorites have been responsible for sudden, catastrophic devastation and major environmental changes. Perhaps, the most plausible explanation to mass extinctions is that multiple factors caused the demise of extremely high percentages of life on earth within a distinct time period. Rather than being an instantaneous event, the changes in numbers of species and in their ability to adapt to environmental change may have been occurring for some time before an extraterrestrial impact pushed surviving species, already on the brink of extinction, over the edge.

Plate Tectonics alone is capable of changing climates over time by opening and closing oceans, uplifting mountain ranges, creating land bridges whereby species can intermingle, transmitting viruses and bacteria to other organisms with no prior immunity. These changes are gradual but, in each generation, may very well affect the development of life on Earth. Volcanism, no doubt, would have affected vast populations, exposing them to toxic gases and causing global climate changes as well. Scientists may never fully understand the complex interplay of events which were ultimately responsible for the mass dying recorded in the geologic record.

23 January, 2006
L. Immoor
BA, MA
Hofstra University
Hempstead, New York
Earth Sciences, Geology