{"id":11865,"date":"2017-03-31T07:32:06","date_gmt":"2017-03-31T07:32:06","guid":{"rendered":"http:\/\/revoscience.com\/en\/?p=11865"},"modified":"2017-03-31T07:32:06","modified_gmt":"2017-03-31T07:32:06","slug":"massive-computer-analyzed-geological-database-reveals-chemistry-ancient-ocean","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/massive-computer-analyzed-geological-database-reveals-chemistry-ancient-ocean\/","title":{"rendered":"Massive, computer-analyzed geological database reveals chemistry of ancient ocean"},"content":{"rendered":"
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A stromatolite from Northern Wisconsin in the courtyard of Weeks Hall on the UW\u2013Madison campus. DAVID TENENBAUM<\/figcaption><\/figure>\n

A study that used a new digital library and machine reading system to suck the factual marrow from millions of geologic publications dating back decades has unraveled a longstanding mystery of ancient life: Why did easy-to-see and once-common structures called stromatolites essentially cease forming over the long arc of earth history?<\/span><\/p>\n

Stromatolites are contorted layers of sediment formed by microbes, and they are often found in limestone and other ancient sedimentary rocks deposited beneath oceans.<\/span><\/p>\n

\u201cGeologists have known for a long time that stromatolites were abundant in shallow marine environments during the Precambrian, before the emergence of multi-cellular life\u201d more than 560 million years ago, says Jon Husson, a post-doctoral researcher and co-author of a study now online in the journal Geology. \u201cBut, stromatolites are rare in the ocean today.\u201d<\/span><\/p>\n

The new study measures the slide in stromatolite prevalence based on descriptions of rocks sifted from more than 3 million scientific publications.<\/span><\/p>\n

\u201cPaleontologists have largely attributed the decline in stromatolites to the evolution of animals, starting some 560 million years ago,\u201d says Shanan Peters, a professor of geoscience at University of Wisconsin\u2013Madison and study first author. \u201cMany multi-cellular animals, like snails, eat microbes. The evolution of these big microbe-grazing animals hit \u2018reset\u2019 on the stromatolite\u2019s world. Or so the story has gone.\u201d<\/span><\/p>\n

The new study found a weak correlation between stromatolite occurrence and the diversity of animals, but a stronger link to seawater chemistry.<\/span><\/p>\n

\u201cThe best predictor of stromatolite prevalence, both before and after the evolution of animals, is the abundance of dolomite in shallow marine sediments,\u201d says Husson. Dolomite is a high-magnesium variety of carbonate, the type of sediment that forms limestone. Dolomite is harder to make than low-magnesium carbonate and it forms today in only a narrow range of marine environments.<\/span><\/p>\n

When the ocean water is super-saturated with carbonate, \u201cthat can make it easier for things like stromatolites to form,\u201d says Husson. \u201cIn Lake Tanganyika [Africa], there are stromatolites forming today, even though there are animals everywhere, snails and fish. The lake is super-saturated with carbonate, and it\u2019s begging to be precipitated. The microbes come along and help it to precipitate, and the result is an abundance of stromatolites.\u201d Elevated carbonate saturation can also help the formation of dolomite, thereby driving the correlation with stromatolites found in this study.<\/span><\/p>\n

Measuring the prevalence of stromatolites through all Earth history is difficult because counting the number of stromatolites alone is not sufficient. You must also know how many rocks could potentially have stromatolites, but do not.<\/span><\/p>\n

The big innovation of this study is the interplay of a new type of digital library and machine reading system called GeoDeepDive with a geological database called Macrostrat. Both were spearheaded by Peters at UW\u2013Madison.<\/span><\/p>\n