[blam]

"As the freeze/thaw cycle does its work, some rocks rise, and other rocks fall through the soil. The net result is a circle of rocks of relatively similar size."

I'm familiar with that action...however, it does not produce iridium or diamonds.

"In samples taken from 15 of the features, Howard and his colleagues found iridium-rich magnetic grains and carbon spherules with tiny diamond fragments similar to those found at Clovis archaeological sites."

[muawiyah]

We are speaking of the ovals and circles on the coastal plaine, right? With the iridium layer being laid down almost simultaneously with the resumption of the freeze-thaw cycle (on a massive scale), all you’ve done is demonstrate that this was a big comet, not that it ploughed holes in the sand.