[meteorite-list] Cratering Interval Results
From: EL Jones <jonee_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:10 2004 Message-ID: <3D41263F.867C4DD7_at_epix.net> <!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> I downloaded the Earth Crater Database this evening and did some simple calculations on ages of craters and intervals between impacts. -- WOW! <br> <blockquote>Using 121 Impact events between 5 million years ago (Pliocene/Miocene boundary) and 650 million years ago (the Vendian Epoch of the Pre-Cambrian), ignoring the dating ± error margins, cratering intervals for Earth were calculated. <p>The average cratering interval is 5.25 million years! <br>The mode is 10 million years between events. <br>More than 80% of the intervals are nearly multiples of 5±0.5, <br>The Standard Deviation (SD) is 9.3 million years. Meaning 68% of the impacts discovered are within 18.6 million years of each other. <br>49 of the 121 (40%) impacts were statistically simultaneous--that is are dated at less than 100,000 between successive impacts. aka "0" <p>The earliest 2 impacts included were 54 and 46 million years apart. If they are excluded the Average interval becomes 4.9 million years and the Standard Deviation then is 7.4 --68% of the time impacts are just under 15 my from each other. <p>Impacts dated before 650 mybp were not included because there is a good chance that most craters before that time did not survive erosion. This was, however, around the time that early protozoan life is thought to have developed and was selected for that reason. Typical intervals between impacts before 650 my are 200-400 million years. The oldest crater identified is 2.023 Billion years old. <p>Impacts later than 5 million tended to be the type of crater which is much smaller than typical and was very likely to survive till present. The interval drops to the the 10's of thousands of years , suggesting that is the "normal" bombardment/flux of lesser impactors which may be distinct from the 5 million year cycle. <p>This does not begin to answer the question about periodic extinctions at 26 million year intervals, however it should be noted that some researchers think they find extinctions (local, regional or global) between 1 and never more than 10 million intervals. Geological ages, incidentally, are divided at major extinction /fauna changes in the fossil record and, the average boundary interval is 41.7 million years not 26 million! <p>The data appears to support a very specific, 5 million year, cycle of major perturbance in the solar system. The fact that the gaps in cratering are multiples of 5 million years lends support to the idea that Earth doesn't catch an asteroid every cycle. <p>Regards, <br>Elton</blockquote> </html> Received on Fri 26 Jul 2002 06:38:21 AM PDT |
 StumbleUpon del.icio.us reddit Yahoo MyWeb
|