Plankton fossils found in 3 billion-year-old rocks Researchers say they ve discovered microfossils of plankton in 3 billion-year-old rocks.  It is surprising to have large potentially complex fossils that far back   says Christopher H. House professor of geosciences at Penn State and lead author of a study published in the journal Geology.The embedded fossils are likely planktonic autotrophs  free-floating tiny ocean organisms that produce energy from their environment.The researchers looked at marine sediment rocks from the Farrel Quartzite in Western Australia. Isotopic analysis using secondary ion mass spectrometry was carried out at UCLA.To determine if these inclusions were actually biological in origin the researchers looked at 15 different samples of Farrel Quartzite and determined their stable carbon isotope ratios.The percentage of carbon 13 in the microfossils was indicative of material produced by biological processes. They found that the carbon 13 percentage in the background organic matter in the surrounding rock was different from that of the microstructures.  When considered along with published morphological and chemical studies these results indicate that the Farrel Quartzite microstructures are bona fide microfossils and support the interpretation that the spindles were planktonic   the researchers write in the journal article.The spindle-shaped microfossils are from 20 to 60 microns in length about the size of fine sand and within the size range of today s microplankton.Stable carbon isotope analysis can determine the biological origin of these microfossils because they used carbon dioxide to create energy and incorporated the carbon into themselves. During this process the organisms selectively incorporate more carbon 12 than carbon 13 from the available carbon producing a signature of biological origin.Dorothy Oehler who is also a co-author and research scientist Astromaterials Research and Exploration Science Directorate NASA/Johnson Space Center notes that the spindles appear to be the same as those found in rocks from the Strelly Pool Formation in Western Australia and the Onverwacht Group in South Africa and Swaziland that are both 3.4 billion years old.  The existence of these microfossils in diverse locations as far back as 3.4 billion years ago suggests that the oceans probably had life in them for a very extended period of time   adds Oehler.   Moreover this has implications beyond what we have done here suggesting the evolution of diverse life proceeded quickly.  Researchers from Nagoya University Japan collaborated on the project.The NASA Astrobiology Institute the Astromaterials Research and Exploration Science Directorate Johnson Space Center and the Japan Society for the Promotion of Science supported this research.Source: Penn StateYou are free to share this article under the Creative Commons Attribution-NoDerivs 3.0 Unported license.