Trace no. 8 This is still another fake fossil. It is not
marks from medusae although it may look like it. Medusae are some
of the oldes organisms on earth. Therefore it has been tempting to
interpretate such structures in preCambrian rocks as biologically
formed.
But this interpretation is problematic for several reasons: First of
all 98% of a medusa is water, meaning that it quickly disappears after
death. Secondly the marks that a medusa makes on the beach very rarely
are preserved. Thirdly, the oldest medusae did not swim but were
attached to the bottom. Fourthly, there are many other processes which
may form concentric rings like these.
This piece is 1 800 000 000 years old (1,8 billion years). It was
found by Peter Haines in Proterozoic rocks in Australia.
It shows sand volcanoes formed when waterfilled sand is compacted under
clay beds. The water become pressed up like a small volcanoe. It is
possible that the form was preserved due to an algae mat.
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