Determining the Size and Energy of the K-T Asteroid

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Description

This activity allows students to calculate the mass, size, and kinetic energy of an asteroid that struck Earth 66 million years ago, based on the total abundance of iridium in a sediment layer. It supports concepts presented in the short film The Day the Mesozoic Died.

The activity begins with students watching the film, which describes the discovery of a layer of clay at the boundary between the Cretaceous and Tertiary rock layers (the K-T boundary). Through chemical analysis, scientists discovered that the layer contained an extraordinary concentration of the element iridium, which is rare in Earth’s crust but common in asteroids and comets. After watching the film, students conduct a series of calculations to estimate the mass and size of the K-T asteroid, based on the total abundance of iridium in the K-T boundary layer. They then estimate the kinetic energy of the meteorite as it struck Earth and compare the amount to that of other high-energy events.

Student Learning Targets

Apply the law of conservation of mass to determine a realistic estimate for the size of a chondritic asteroid necessary to supply the global abundance of iridium in the K-T boundary layer.
Estimate the kinetic energy of an extraterrestrial impacting body.
Identify changes in forms of energy resulting from the K-T impact.
Evaluate the degree of energy necessary to produce global change in Earth’s ecosystems.

Estimated Time

One 50-minute class period.

Key Terms

asteroid, density, heavy elements, iridium, kinetic energy, mass, meteor, meteorite, surface area, velocity

Primary Literature

Alvarez, Luis W., Walter Alvarez, Frank Asaro, and Helen V. Michel. “Extraterrestrial cause for the Cretaceous-Tertiary extinction.” Science 208, 4448 (1980): 1095–1108. https://doi.org/10.1126/science.208.4448.1095. To access this article, set up a free AAAS account.

Smit, J., and J. Hertogen. “An extraterrestrial event at the Cretaceous-Tertiary boundary.” Nature 285, 5762 (1980): 198–200. https://doi.org/10.1038/285198a0.

Terms of Use

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