The Impact Hypothesis for the K-T Mass Extinction Essay


Cretaceous–Paleogene extinction event is one of the key events in the past of the planet that holds the key to understanding the widespread of mammal species today. As of now, there is no widely agreed theory that would explain it. The most viable hypothesis was proposed by Alvarez in 1980: it argued the extraterrestrial origin of the extinction, citing the layer of iridium which is a material that is rarely found on the planet, but is quite often found in the stars. It was supposed that a big asteroid hit the Earth, burning a considerable amount of its mass in the atmosphere, thus creating darkness that killed the plants and deprived the animals of food. The paper also reflects on other studies that refute this hypothesis.


It would not be correct to believe that the current balance in the biosphere could be traced to the beginning of life. Quite the opposite, the planet experienced several extinctions that wiped out a considerable number of species. A good example of such extinctions is the one that is associated with Cretaceous–Paleogene. The evidence suggests that almost three-quarters of species of the planet extinct. While this might be seen as an event that provided the mammals with the opportunity to populate the Earth, it is obvious that the scholars should examine the reasons for this distinction. At the present moment, Cretaceous–Paleogene extinction event gave rise to a heated scientific debate. The impact hypothesis, presented by Alvarez, seems to offer the most plausible explanation. However, some scholars reject it all together. This paper will examine the major aspects of this, also involving works of other scholars to support or refute it.


To begin with, it may be useful to turn to the original text that presented this hypothesis. Thus, in 1980, Luis W. and Walter Alvarez, together with some colleagues wrote and article that assumed that Cretaceous-Tertiary extinction was triggered by an extraterrestrial object, namely an asteroid impact. Here is the reasoning of the scholars: they point out that platinum metals, like iridium, are quite rare in the Earth’s crust, but are quite common among the stars (Alvarez, Alvarez, Asaro & Michel 1980). That is why any increase in the amount of this group of metals should draw attention of the scholars. It was found in all over the world, there are traced of iridium on the boundary of Cretaceous period which also coincides with mass extinction (Alvarez, Alvarez, Asaro & Michel 1980). So, the scholars suggest that an impact of an asteroid could release a lot of iridium into the atmosphere as it was burning, thus triggering darkness and death of plants which resulted in the death of animals as well (Alvarez, Alvarez, Asaro & Michel 1980). The article estimates that the asteroid in question could have been 10 kilometers in diameter.

Clearly, this is a hypothesis that seems to be quite plausible. However, there are several scholars that reject it. A good example is an article by Keller et al (2004). In the article, the scholars point out that Chicxulub crater was made by a big asteroid that fits the description of Alvarez; however, the impact may have taken place 300,000 years before the extinction (Keller et al 2004). Therefore, the impact hypothesis makes a wrong causation which is based on incorrect interpretation of available facts. In other words, the impact of the asteroid did take place, but it could not have triggered the mass extinction with the help of darkness due to large about of dust dispersed in the atmosphere. One should also note that this article approaches the issue from a number of perspectives, successfully proving the validity of its point.

One should also note that the interest towards impact hypothesis has not disappeared and many of the contemporary scholars support it. For example, Schulte et al (2010) wrote an article that did not only support the theory, but also adjusted it to make sure that it matches the available evidence, thus making it more accurate. For example, other than stating that the extinction happened 65 million years ago, the scholars made the number more accurate – 65.5 million years (Schulte et al 2010). In addition to that, the authors also explore the so-called “ejecta-rich deposits” which are thought to have been formed by the debris of the asteroid (Schulte et al 2010). As a result, the article is more detailed about the process of extinction, pointing out that environmental perturbations such as “darkness and cooling” are responsible for it (Schulte et al 2010)


Having examined all the points that were mentioned in the paragraphs above, one is able to come to the following conclusion: Cretaceous–Paleogene extinction is an event that is not fully explained and understood yet; that is why it is necessary to develop several hypotheses that would shed light on it. Though it is opposed by some, the impact hypothesis by Alvarez seems to be the most viable at the moment. It was originally proposed in 1980 and relies in the global deposit of iridium that can be found virtually anywhere I the world. The authors believe that it is the debris of a big asteroid that burned in the atmosphere and resulted in darkness that made three-quarters of the plants and animals extinct. While there are some studies that seem to refute it, the interest towards impact hypothesis is high.


Alvarez, L., Alvarez, W., Asaro, F., & Michel, H. (1980). Extraterrestrial Cause For The Cretaceous-Tertiary Extinction: Experiment And Theory. Applications of Space Developments, 241-271.

Keller, G., Adatte, T., Stinnesbeck, W., Rebolledo-Vieyra, M., Fucugauchi, J. U., Kramar, U., & Stüben, D. (2004). Chicxulub impact predates the KT boundary mass extinction. Proceedings of the National Academy of Sciences of the United States of America, 101(11), 3753-3758.

Schulte, P., Alegret, L., Arenillas, I., Arz, J. A., Barton, P. J., Bown, P. R., … & Collins, G. S. (2010). The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary. Science, 327(5970), 1214-1218.

The terms offer and acceptance. (2016, May 17). Retrieved from

[Accessed: October 27, 2021]

"The terms offer and acceptance.", 17 May 2016.

[Accessed: October 27, 2021] (2016) The terms offer and acceptance [Online].
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[Accessed: October 27, 2021]

"The terms offer and acceptance.", 17 May 2016

[Accessed: October 27, 2021]

"The terms offer and acceptance.", 17 May 2016

[Accessed: October 27, 2021]

"The terms offer and acceptance.", 17 May 2016

[Accessed: October 27, 2021]

"The terms offer and acceptance.", 17 May 2016

[Accessed: October 27, 2021]
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