More scientific but there is a paywall: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1977.html http://www.nature.com/ngeo/journal/vaop/ncurrent/ful

More scientific but there is a paywall: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1977.html http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo19...