Assignment 4

Due: on or before November 12, 2021

Exercise 4: Cratering Frequency on the Earth

In this exercise, you will make rough estimates of the rate of cratering on the Earth; solarviews.com/eng/tercrate.htm is a nice reference for Terrestrial impact craters.


1. Fill in Tables 1 and 2 using the crater list found on Views of the Solar System; http://solarviews.com/eng/crater.htm (the link found on the site solarviews.com/eng/tercrate.htm above).

Table 1: Terrestrial Craters: Craters Younger and Older than 300 Million Years

Crater Size

Number of Craters ≥ 300 My

Age of the Oldest Crater in Group

Number of Craters < 300 My

Age of the Oldest Crater in Group

D ≥ 151 km

craters

My

craters

My

150 km ≥ D ≥ 101 km

craters

My

craters

My

100 km ≥ D ≥ 51 km

craters

My

craters

My

50 km ≥ D ≥ 11 km

craters

My

craters

My

10 km ≥ D ≥ 1 km

craters

My

craters

My

D < 1 km

craters

My

craters

My

Table 2: Total Numbers of Terrestrial Craters

Crater Size

Number of Craters in Group

Age of the Oldest Crater in Group

D ≥ 151 km

craters

My

150 km ≥ D ≥ 101 km

craters

My

100 km ≥ D ≥ 51 km

craters

My

50 km ≥ D ≥ 11 km

craters

My

10 km ≥ D ≥ 1 km

craters

My

D < 1 km

craters

My

Note--On website, Ma stands for million years. Here, My stands for million years



2. How accurate are of your crater numbers? What are sources of error (uncertainties) are there in your estimates? Do you think you are counting all of the impacts over the last few billion years? Looking at the results in your results, give some reasons that support your answer. What are the ages of the oldest small craters? How do the ages of larger craters compare to the ages of the smallest craters? What do these results suggest to you?




4. Roughly, estimate how often do we suffer big hits? ____________________________ Define a big hit as an event that produces a crater with diameter larger than 100 km or so. Roughly when was the last big hit? __________________________________ Note that the Chicxulub crater, the purported dinosaur killer left a crater ~ 170 km in diameter and so is considered a big hit in our definition.

5. Roughly, how often do we suffer hits of size 10 to 50 km? ____________________________

6. Are your crater numbers consistent with the result that the cratering rate for the Moon increased by nearly a factor of 3 around 290 million years ago?