Evidence for early life in Earth’s oldest hydrothermal vent precipitates

Abstract

There are no confirmed microfossils older than 3,500 million years (Myr) on Earth, probably because of the highly metamorphosed nature of the oldest sedimentary rocks 1 . Therefore, studies have focused almost exclusively on chemical traces and primarily on the isotopic composition of carbonaceous material,which has led to controversies regarding the origin of isotopically light reduced carbon 2 . Schists from the approximately 3,700-Myr-old Isua supracrustal belt in southwest Greenland contain up to 8.8 wt% graphitic carbon that is depleted in 13 C, and this depletion has been attributed to biological activity 3,4 . However, because non-biological decarbonation reactions and Fischer-Tropsch-type synthesis 5 can produce reduced Page 1 of 11 carbon with similar isotopic compositions, non-biological interpretations are possible 2 . Apatite with graphite coatings, within iron formations from the ca. 3,830-Myr-old Akilia supracrustal belt in southwest Greenland has been interpreted as the metamorphosed product of biogenic matter 6 , supported by the presence of biologically important heteroatoms within the graphite 7,8 . However, it has been suggested that some graphite in the Akilia iron formations was deposited by metamorphic fluids 8,9 . This latter interpretation is echoed in the Nuvvuagittuq supracrustal belt (NSB) by the presence of poorly crystalline, fluid-deposited graphite that coats apatite 10 , demonstrating that some apatite-graphite occurrences are produced abiotically during fluid remobilization and high-grade metamorphism.The NSB in northeastern Canada represents a fragment of the Earth's primitive mafic oceanic crust.The NSB is composed predominantly of basaltic metavolcanic rocks (Extended Data Fig. 1 Data Fig. 2). The presence of well-preserved, 20-3,000-µm chalcopyrite crystals within the NSB jasper and carbonate iron formations (Extended Data Fig. 3a) demonstrate the lack of postdepositional oxidation.Most NSB rocks were subjected to upper amphibolite-facies metamorphism around 2,700 Myr ago 14,20 . Here we describe parts of the NSB that were less affected by deformation (Supplementary Table 4) and focus on sites where metamorphic grade appears not to have exceeded lower amphibolite facies 17 . This setting is evidenced by local outcrops in the southwestern margins of the belt that preserve primary chert, diagenetic calcite rhombohedra with poikilitic textures, and minerals of low metamorphic grade such as euhedral stilpnomelane and minnesotaite in chert that lack pseudomorphic retrograde textures.

Frequent Flaring in the TRAPPIST-1 System—Unsuited for Life?

“…These questions on habitability are important, since the estimated age of TRAPPIST-1, which is at least 500 Myr (Filippazzo et al 2015) (Luger et al 2017 estimated 3-8 Gyr) could make possible the formation of life in ideal conditions, as the earliest life on Earth dates back to approximately 4 Gyrs (Dodd et al 2017), although complex life took much longer time to form (see Grosberg & Strathmann 2007 and references therein).…”

Hot Spring Microbial Community Composition, Morphology, and Carbon Fixation: Implications for Interpreting the Ancient Rock Record

“…As a result, geothermal springs in and near the 640,000 year old caldera in YNP are typically silica-saturated (Fournier, 1989) and serve as a proxy for ancient oceans at or near silica saturation. In addition, silica-saturated geothermal systems like those in YNP are ideal locations for understanding early life because: (1) there is evidence for the presence of geothermal systems throughout Earth's history (e.g., Djokic et al, 2017;Dodd et al, 2017); (2) they often harbor deep-branching microbes (Pace, 1997;Reysenbach and Shock, 2002); and (3) physicochemical conditions of the hydrothermal water excludes multicellular life enabling the formation (and preservation) of microbial structures in the absence of grazing. The Greater Obsidian Pool Area (GOPA) in the Mud Volcano Area of YNP contains silica-rich geothermal springs that are host to filamentous and microbial mat communities as well as stromatolites.…”

Ilvaite–manganilvaite series minerals in jasper and iron–manganese ore from the Northern Chichibu belt, central Shikoku, Japan

“…Microfossil-like objects in Precambrian jasper have attracted the attention of some researchers owing to their potential implications for the origin of life near a deep sea hydrothermal vent (Dodd et al, 2017). Jasper lenses in the present study are much younger (Early Permian deposition), but ilvaite spherules have some similarities to microfossils.…”