Various explanations for the presence of what look like ripples or creases in sedimentary rocks have been proposed over the years. Some see them as evidence of long periods such as the Milankovitch cycles, and others see them as seasonal tide lines (a very short period as far as geochronology is concerned). At http://archaeologynewsnetwork.blogspot.co.uk/2014/09/ripples-in-ancient-… … we have an even shorter stretch of time. We are asked to remember walking along the sea shore and looking at the rippled patterns in the sand or shingle formed by the ebb and flow of waves – which occur in moments rather than annually or in thousands of years. Such ripples, we are told, as embedded and preserved in ancient rocks, seem to be especially common after extinction events – which may call for some scepticism. MIT researchers see the ripples, or wrinkles (an alternative way of describing them) are based on wave action, fossilised features that may be a vestige of microbial life – which has disappeared but left the pattern in their wake.