Exercise 4: Cratering Frequency on the Earth

Due: February 14, 2019, complete exercise in class

Make rough estimates of the rate of cratering on the Earth using Tables 1 and 2 filled in at home (using the crater list found on Views of the Solar System; http://solarviews.com/eng/crater.htm )

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

Crater Size	Number of Craters Older than 300 My	Age of the Oldest Crater in Group	Number of Craters Younger than 300 My
D ≥ 151 km	craters	My	craters
150 km ≥ D ≥ 101 km	craters	My	craters
100 km ≥ D ≥ 51 km	craters	My	craters
50 km ≥ D ≥ 11 km	craters	My	craters
10 km ≥ D ≥ 1 km	craters	My	craters
D < 1 km	craters	My	craters

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--In the Table on the link, Ma stands for million years;in the above table My stands for million years

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2. How accurate are your derived cratering numbers? What are the possible sources of error in your estimate? [that is, Do you think you are counting all of the impacts over the last few billion years? Why or why not.]

How do you think your crater numbers compare to those found for the Moon? If you think the numbers are larger than, the same as, or smaller than those for the Moon, explain how you arrived at your answer.

3. Fill in the cratering rate table below (Table 3). Use the data from your Tables 1 and 2.

Table 3: Cratering Rates for those Younger than and Older than 300 My

Crater Size	Time between Impacts: Craters Older than 300 My	Time between Impacts: Craters Younger than 300 My	Time between Impacts: all Craters
D ≥ 151 km	My	My	My
150 km ≥ D ≥ 101 km	My	My	My
100 km ≥ D ≥ 51 km	My	My	My
50 km ≥ D ≥ 11 km	My	My	My
10 km ≥ D ≥ 1 km	My	My	My
D < 1 km	My	My	My

Note--In the above table My stands for million years

4. Roughly, how often do we suffer big hits? ____________________________ Define a big hit as an event that produces a crater with diameter larger than 101 km. Roughly, when was the last big hit? __________________________________ Note that the Chicxulub crater, the purported dinosaur killer left a crater ~ 170 km in diameter.

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

6. Are your results consistent with the idea that the cratering rate for the Moon increaed by nearly a factor of 3 around 290 million years ago?