Early life on Earth
A New Twist on the Evidence of Earliest Life on Earth The oldest undisputed traces of life on Earth are represented by graphite globules in >3.7 Ga rocks from the Isua supracrustal belt in west Greenland. The geological setting is interpreted as a low-strain tectonic domain (greenschist and amphibolite facies) with primary features such as pillow lavas, pillow breccia, cherts, banded iron formaions, as well as sedimentary features such as greywacke and hemipelagic deposits. This interpretation is consistent with a marine supracrustal depositional environment influenced by hydrothermal vents (that deposited sulfides, iron oxides and exhalative quartzites), gravity flows, and intermediate pelagic sedimentation, i.e. similar to exhalative ore formations of various ages located at numerous sites around the world. To evaluate a possible biological origin of such graphitic globules in wacky deposits, Dr. Tomas Hode and his colleagues are investigating an analogous setting in eastern Jämtland, Sweden. The eastern Jämtland rocks (~1.9 Ga) consist of well preserved greywacke, black schist, pillow lavas, exhalative quartz-banded iron- and sulfide-rich deposits similar to small-scale algoma-type BIF-settings, with a metamorphic grade that ranges between upper greenschist and amphibolite facies. Graphite is associated with black schist, greywacke, and exhalative banded quartz- and iron-rich deposits. The mode and occurrence of the graphite, as well as the geological setting and the sedimentary sequences in the studied area, show strong similarity to the Isua rocks as described by Rosing (1999), and may therefore be considered a good analogue to the Isua setting. Extracellular polymeric substances as a biomarker in the fossil record Text to be added.