SEE MASS EXTINCTION, OR NOT PAGE RETURN TO THE THEORIES OF THE TRIASSIC EXTINCTION PAGE GO TO RELATED WEBSITES PAGE WITH LINKS GO TO THE GLOSSARY
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BOLIDE IMPACTS

  Bolide impacts, also known as Meteorites have been attributed as the cause of other mass extinctions and most famously the K-T event. The K-T event occurred at approximately 65 Ma and is believed to be the trigger of the dinosaur extinction. It therefore seems possible that this theory may be applicable to the end-Triassic mass extinction at 210 Ma.

Picture of the Hale Bopp comet

 

In fact it is the work of Alvarez et al 1980 on the K-T boundary that has generated the growing interest on whether these large bolide impacts could have influenced the history of life.

 

In order to have any basis for the proposal of a bolide impact as the trigger of the end-Triassic, or in fact any mass extinction, there are certain pieces of evidence, which need to be found. These pieces of evidence can be thought of as the ‘fingerprints’ at a crime scene and if properly constrained can confirm or reject the suspect; in this case the theory of a meteoritic impact. Below is a list of some evidence that Earth Scientists and other scientific professionals may look for in the field or through analytical methods in the laboratory…

 

Crater – perhaps the most important piece of evidence as this shows where the impact occurred, how large it was and this allows calculation on how destructive it could have been.

 

Iridium anomalies – these may be found in sediments at various locations around the globe at the time boundaries of large impacts e.g. the K-T event.

 

Shocked quartz – which confirms the occurrence of an enormous release of energy in the form of heat and pressure over a very short period of time, examples of this can be a nuclear explosion or meteoritic impact.

 

Tsunami deposits – these can be caused by the shock waves released at an impact site, you may expect these to be found on continents with rocks from the age of the impact. Deposits may include very mixed up sediments from various locations due to the high energy being carrying material great distances through shallow marine environments and occasionally travelling kilometres inland, before loosing energy and depositing the load.

 

The main contender in terms of a crater location for the cause of the mass extinction is named the Manicougan. The Manicougan crater is located in Quebec (south eastern Canada), and is thought to be the largest impact structure known from the Phanerozoic. The crater has a diameter of roughly 100 km (Grieve, 1987). However the question still remains; is this the remains of what caused the observed mass extinction? In order to answer this question, it is necessary to accurately date the impact structure and boundaries of the Triassic/Jurassic sediments found around the world. Once the two dates have been agreed on it is then possible to compare them to one another and this will either show the theory is possible (if the dates match) or the theory should be rejected (if the dates do not match). Olsen et al, 1987 believes that the Manicougan is the best candidate based on a 214±5 Ma age from Jahn et al, 1978. More recent research has shown that the impact melt within the crater has an age of 214±1 Ma. The date of the boundary has also been placed at 202±1 Ma. Both ages are gained by using more accurate forms of radiometric dating, in particular U-Pb zircon dating. So the evidence points towards the Manicougan impact preceeding the end of the Triassic by approximately 12±2 Ma, therefore it could not be the cause of the observed mass extinction (J.P.Hodych, G.R.Dunning, 1992).

Picture from www.earthchangestv.com

 

In relation to this discovery it has now been proposed that there was also a mass extinction earlier in the late Triassic (Carnian/Norian boundary). The Thecodontians and many mammal-like reptiles went extinct at this stage and this is the widely accepted view of how the Dinosaurs attained dominance, as there were fewer predators to compete with (M.J.Benton, 1986 and M.J.Benton, 1988). This could have been formed by the Manicougan impact (Olsen et al, 1987) because the 214±1 Ma date overlaps the 223±9 Ma date of the Carnian/Norian boundary (Harland et al, 1990).

   

SEE MASS EXTINCTION, OR NOT PAGE RETURN TO THE THEORIES OF THE TRIASSIC EXTINCTION PAGE GO TO RELATED WEBSITES PAGE WITH LINKS GO TO THE GLOSSARY
GO TO AN INTRODUCTION ON THE EFFECTS OF AN IMPACT (IN RELATION TO THE K-T EVENT)