Hadean - Early Archean: 4.4 to ~ 3.5 Ga How to build a habitable planet? Jack Hills in Australia meta-conglomerat with the oldest minerals on Earth 4.4 Ga Geological time scale 1 : Hadean 2 : Archean Quasi no rock record Rock record First cooling of magma ocean Alteration of basalt to produce serpentinite crust ~ as today on seafloor 146 142 Sm → Nd (T1/2= 103 Ma) silicate/silicate fractionation before total decay of 146Sm ⇒ < 150 Ma, done early Hadean Acasta (Canada) oldest rocks on Earth, end of Hadean, 4.01 Ga Acasta (Canada) oldest rocks on Earth, end of Hadean, 4.01 Ga Acasta (Canada) oldest rocks on Earth, end of Hadean, 4.01 Ga Zircon ages Jack Hills (Australia) meta-conglomerat Archean in age but contains very old zircons Jack Hills (Australia) meta-conglomerat Archean in age but contains very old zircons Jack Hills (Australia) meta-conglomerat Archean in age but contains very old zircons ZrSiO4 1 mm U-Pb age at 4.4 Ga Part of the grain crystalized shortly after end of magma ocean Age distribution of zircons Different dates on different zircon layers Several age populations Oldest Quartz, micas and plagioclase ∂18O in zircons = 5 to 7.4 ‰ Original magma’s = ∂18O ~ 8.5 to 9.5‰ (La/Lu)N zircons⇒(La/Lu)N of magma~ 200 = TTG magma 4.4 Gyr zircons not so different from actual zircons Granitic inclusions present in zircons Quartz, micas and plagioclase ∂18O in zircons = 5 to 7.4 ‰ Original magma’s = ∂18O ~ 8.5 to 9.5‰ (La/Lu)N zircons⇒(La/Lu)N of magma~ 200 = TTG magma 4.4 Gyr zircons not so different from actual zircons Continental crust & oceans in Hadean Granitic inclusions, quartz, micas, plagioclase La/Lu data same as Archean crust Stable continental crust at 4.4 Ga ∂18O indicates that magma interacted with relatively cold water (~ 70 ºC) Liquid water is present Ocean present at 4.4 Ga Looks like Hadean already was habitable “cool early earth” (but was it inhabited?) Implications for the origin of life Early Hadaen (4.568-4.40 No life possible Ga) Magma Ocean Late Hadaen (4.40- 4.00 Conditions favorable Ga) Continental crust + liquid water for life ocean Late heavy bombardment Sterilization ?? Archean (4.00 – 2.50 Ga) Life is present Continents, oceans, plate tectonic, etc. Between 4.0 and 3.8 Ga Late heavy bombardment Between 4.0 and 3.8 Ga Collisions - impacts all over solar system NASA deep impact Hubble ST Fragment G impact Asteroid Eros 1 km 1994 Shoemaker-Levy 9 on Jupiter 33x13x13 km Surface comet Tempel 1 Mare Orientale on the Moon ~ 930 km multi-ring crater 140 km crater on Europa’s ice Collisions - impacts all over solar system NASA deep impact Hubble ST Fragment G impact Asteroid Eros 1 km 1994 Shoemaker-Levy 9 on Jupiter 33x13x13 km Surface comet Tempel 1 Mare Orientale on the Moon ~ 930 km multi-ring crater 140 km crater on Europa’s ice Collisions - impacts all over solar system NASA deep impact Hubble ST Fragment G impact Asteroid Eros 1 km 1994 Shoemaker-Levy 9 on Jupiter 33x13x13 km Surface comet Tempel 1 Mare Orientale on the Moon ~ 930 km multi-ring crater 140 km crater on Europa’s ice Cratering event on solid surface Cratering event on solid surface Cratering event on solid surface Cratering event on solid surface Suevite Cratering event on solid surface Suevite Melt-rock Cratering event on solid surface Suevite Fractured breccia Melt-rock Cratering event on solid surface Shocked minerals Suevite 100 µm Fractured breccia Melt-rock Tektites Cratering event on solid surface 1 cm Shocked minerals Suevite 100 µm Fractured breccia Melt-rock 3.4 Comparative stratigraphy of 3.5 Early Earth and Mare Lavas 3.6 Moon Orientale 3.7 Schrödinger Nulliak Quartzite 3.8 Cluster of Lunar Imbrium Early Amitsôq Gneiss Imbrian craters around Sereniatis LH B Isua Gneiss & Crisium 3.9 4.0 to 3.8 Ga Nectaris 4.0 Oldest Acasta Gneiss impact melt 4.1 4.2 4.3 4.4 Oldest Jack Hill Zircon Anorthosite crust Origin of 4.5 Origin of Moon Earth Late heavy bombardment 2 hypotheses Slow decline Rapid decline but short peak Cool early earth Another ? Archean rate Hadean Archean Arguments for the LHB ~ 3.9 Ga max. age of Lunar impact melt and = shock degassing ages of Lunar and Martian meteorites How to preserve ancient Lunar crust (4.4 Ga old anorthosites) if elevated bombardment in Hadean ? No elevated PGE in Lunar crust contrary to what expect if bombardment constant over 500 Myr (based on available samples) LHB = mass added to the Moon = 2x1013 g/an if extrapolated over whole Hadean > Lunar mass or Moon formed at ~4.1 Ga Terrestrial zircons do not show shock features and formed on a rather cool Earth Traces of LHB on Earth ? No impact marker in Isua (shocked qz, PGE) LHB missed Earth ? Chronology problem: LHB terminated before Isua Traces erased by sedimentation and erosion Search for it on other planets Extrapolate Moon data to Earth Moon: 1700 craters > 20 km, 15 > 300 -1200 km, multiple ring basins Earth: > 10 000 craters > 20 km, 200 > 1000 km, 1 crater 20 km every 104 years Possible consequences Vaporize all of part of oceans, ejection of atmosphere Large basins are formed Volcanism, fracture of oceanic crust Contribution of OM, and noble gases Impact rate and Hadean environments Hadean impact rate is elevated no life possible (hyp. 1) Cool early Earth hypothesis and effect of LHB Low impact rater : life originates in Hadean (hypothesis) Complete extinction during LHB, second start in Archean Major Hadean diversification but mass extinction during LHB, only hyperthermophiles survive on deep ocean floor, and radiate in Archean Major Hadean diversification but mass extinction during LHB, bottleneck effect, new radiation during Archean Origin and cause of LHB Models show that 0.350 to 1.2 Ga after formation of solar system, gas planets migrate towards their current orbits (Jupiter and Saturn inward, Neptune and Uranus outward) Destabilize orbits of asteroids and comets Objects come flying towards inner solar system Impact craters (basins) as a craddle for life ? hypothesis of origin in hydrothermal vents handicaped by high vent Tº > 350 ºC destroys all organic molecules Melt-rock generates hydrothermal circulation Important extension of hydrothermal environments in the crater, life > 106 year, enough to concentrate complex organic molecules Ries (25 km), Manson (35 km) and Puchezh-Katunki (80 km) mineralogy show temperature gradients 400 to < 100°C. Crater contains highly fractured and brechiated rocks, inducing active circulation and micro- environments with exposed mineral surfaces to favorable help catalyze pre-biotic chemistry Complex organic molecules delivered by the projectile Yellowstone Geyser system, complex biosphere Stromatolites first form to recolonize Ries crater lake Do complex organic molecules survive an impact ? Complex organic molecules are destroyed by the high temperatures generated by impact (Chyba et al., 1990) Still valid for asteroidal projectile at ~ 20 km/s Computer model : amino acids survive a cometary impact in the ocean Comet volatile and ice-rich, easily vaporized but the high energy cloud cools rather quickly The lower the impact angle, the lower temperature in the cloud, the higher the survival rate of organic molecules Text Oblique (angle < 15°) impact of a comet in the ocean could spread (> 10%) of its amino acid content Such impacts are rare, but considering impact rate in the Hadean or during LHB, they could have contributed to the concentration/reaction of amino acids in the oceans Association amino acids and altered clay particles (spherules) offer surface for pre-biotic chemistry ? Archean impact rate ? Ejecta layer Location Age (Ga) Thickness cm Acraman Australia 0.59 40 Sudbury Ontario 1.86 25 to 70 Ketilidian Greenland ~ 2.0 100 Dales Gorges Australia 2.48 30 Wittenoom Australia 2.54 100 Revilio Australia 2.56 20 Carawine Australia - S. Africa 2.63 2470 S4 (Barberton) South Africa 3.24 15 S3 (Barberton) South Africa 3.24 200 S2 (Barberton) South Africa 3.26 310 S1 (Barberton) South Africa 3.47 35 KT World 0.065 few cm (to 1 m) Archean and Proterozoic impact layers 1 cm 0.5 mm Impact ejecta layer Wittenoom, Australia Comparison Cretaceous-Tertiary layer 10 km impact 65 Ma ago Archean and Proterozoic impacts Ejecta layers thick and with large impact spherules, PGE anomaly but rare shocked grains Spherule composition originally basaltic, associated with tsunami deposition Large size impacts: > KT boundary, projectiles 20 to 50 km? Oceanic impacts ? Detection coincidence ? impact rate > today, peak in bombardments ? How did life cope with elevated rate ? Geological time scale 1 : Hadean 2 : Archean Quasi no rock record Rock record Archean continental crust: a long record Isua gneiss, sedimentary rocks, Greenland dated at 3.865 Ga Deposited as turbidite Amitsôq gneiss, plutonic rocks, Greenland dated at 3.82 Ga Magmatic origin Current distribution of Archean terranes Gneiss of Shaw (Australia) at 3.45 Ga Swaziland gneiss complex at 3.644 Ga Greenstone belts Banded Iron formation Barberton, komatiite, Gopping Gap, Pilbara, South Africa Australia 3.445 Ga 3.5 Ga Chert, Barberton, 3.445 Ga Pilbara, Australia 3.5 GA Shark bay Australia today Are these equivalent to stromatolites ? Films of Cyanobacteria trapping sedimentary grains in shallow water environments Greenstone belts Tholeitic basalt Grauwackes Kuhmo, Finland Kuhmo, Finland 2.65 Ga 2.65 Ga Late Plutonic rocks Granodiorite of Arola, Finland 2.65 Ga Proportion of Archean terranes Kuhmo, Finland 2.7 Ga Arola, Finland 2.7 Ga Gurur, India 3.1 Ga Komatiites: evidence for a warmer Archean Earth Magmatic rock that does not exist after end of