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).
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 |
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?