Disappearance of World’s Oldest Fossils Solved
The widespread and unusual disappearance of stromatolites, the oldest known fossils on Earth, may have been caused by the presence of single-celled organisms called foraminifera.
Stromatolites (“layered rocks”) are one of the most intriguing fossils known to science as they date back some 4 billion years and provide a snapshot of the emergence of life on Earth. They are the only fossils that encode the first 7/8 th of the history of life on earth, revealing fascinating information about the role that ancient microorganisms played in the evolution of life and in shaping earth’s environments. Today, stromatolites are nearly extinct in marine environments, living a precarious existence in only a few localities worldwide.
Stromatolites are structures made of calcium carbonate and shaped by the actions of microbes that trapped grains of coastal sediment into fine layers. They were in great abundance along shorelines all over the world about 3.5 billion years ago and dominated the scene for more than two billion years. However, around 1 billion years ago, their numbers mysteriously dropped until the point of almost complete eradication. Living stromatolites can still be found today, scattered across just a few localities worldwide.
The dramatic loss of the stromatolites has been perplexing scientists for many years. Some believe that it may be linked to the sudden appearance in the fossil record of different formations called thrombolites (“clotted stones”), which are produced through the action of microbes on sediment and minerals. Unlike stromatolites, they are clumpy, rather than finely layered. It was suggested that either stromatolites became thrombolites, or thrombolites arose independently of the decline in strombolites.
However, recent findings made by a team of scientists in the US and published in the Proceedings of the National Academy of Sciences, may provide the key to unlocking the mystery. The team of researchers discovered that foraminifera, amoeboid protists, may have played a role. The researchers started with samples of modern stromatolites from Highborne Cay in the Bahamas and seeded them with foraminifera. After about six months, the finely layered arrangement characteristic of stromatolites had transformed to a jumped arrangement more characteristic of thrombolites. The results indicate that active foraminifera can reshape the fabric of stromatolites and could have instigated the loss of those formations and the appearance of thrombolites.