Pondering the Precambrian #42

Proterozoic:

NeoProterozoic:

Changes to the carbon cycle and environment  were detected from the Ediacaran/Cambrian boundary in China.

Using boron to detect the salinity of the paleooceans gives some interesting twists.

Evolution of multiple basins from the Neoproterozoic are described.

Is there a biochemical signal dividing metazoan clades into two?

Did animal-like embryos predate actual metazoans (animals).

How NOT to become a metazoan.

A Cryogenian interglacial deposit has been found in China.

When did the Sturtian glaciation begin during the Cryogenian in South China?

Mesoproterozoic:

Where was South China in the Nuna/Columbia and Rodinia supercontinents during the Mesoproterozoic?

The Stenian Copper Harbor and Nonesuch Formations have a marine origin.

PaleoProterozoic:

Evidence of explosive basalt volcanism found from the paleoproterozoic.

In French Guiana, a gold rich Rhyacian Period formation has been found.  It contains sedimentary layers within the volcanic ones.  Are they fossiliferous?

After the Lomagundi-Jatuli Event, the carbon-sulfur cycle seemed to return to strong activity in the aftermath in the Rhyacian/Orosirian Periods.

Archean:

It appears during the GOE, the ocean basins remained anoxic.

Earth's magnetic field may have been in place during the Archean.

Evidence of subduction from the Late Archean comes from Australia.

The Kaapvaal Craton may be a remnant of the Pilbara Craton that split off in the MesoArchean.

Extraterrestrial impacts might have triggered bursts in plate tectonics.

Ancient microbes played an important role in warming the early Earth.

Hadean:

The impact history of Earth should NOT be correlated to other planets in the solar system.

Origin of Life:

There is a hyperacidic, hypersaline geothermal system in Dallol, Ethiopia that is lifeless and that has implications for the origin of life.

DNA is only one of several possible genetic information molecules.

Lifelike chemistry has been created in the lab.

Ribose and other sugars have been found in meteorites.

Some of the earliest animal fossils are possibly chemical 'gardens' that produce pseudofossils.

Pondering the Precambrian #41

Proterozoic:

Glauconite is rare is precambrian deposits of the Bhima Basin.  Why?

NeoProterozoic:

There is evidence of the oxygen and other environmental conditions across the Ediacaran/Cambrian boundary from southern China.

Could the marine waters have been highly alkali at the terminal Ediacaran?

Cloudina acted as an anchor for Ediacaran reefs.

Sulfur and carbon cycles from the Ediacaran formations of the Lower Yangtze block.

Oxygen levels during the NeoProterozoic were transient.

There were two episodes of phosogenesis in the ocean water of the Doushantou formation.

The Doushantou and Datangpo formations from the Ediacaran and Cryogenian have been argued to represent evidence of photosynthetic productivity during the Snowball Earth episodes.  This is probably wrong.

There is evidence from India of biofilms from the Neoproterozoic.

The microfossils of the Katanga Supergroup are probably pseudofossils, alas.

Boxonia bearing stromatolites from Mongolia suggest variation in their formation compared to others.

Ediacaran Biota-like disc fossils have been found in the Cryogenian, 80 million years earlier than ever before.

The Cryogenian basin deposits of south China suggest massive hydrothermal activity during the Sturtian Glaciation (Snowball Earth).

What was the stratosphere of the Snowball Earth like?

The Tonian Callana Group has a carbon anomaly that does not match the one observed at Bitter Springs.

MesoProterozoic:

There is evidence of the breakup of the Columbia Supercontinent from Brazil.

PaleoProterozoic:

Kimberlites from the Siderian suggest there is an isolated mantle reservoir.  And may be fingerprints of the ancient makeup of the world's geology.

There was a very long lived tectono-magmatic event 1.8 billion years ago.

The geochronology of the Hart Dolerite of Australia is documented.

Archean:

There is evidence of oceanic crust subduction from the NeoArchean.

There is also evidence of mountain building from the NeoArchean.

There is evidence of a subduction/accretion/collision event at the end of the NeoArchean, confirming full blown plate tectonics were in progress at that time frame.

Mesoarchean deposits from islands suggest the pelagic environment was rich in boron.

Paleoarchean microfossils show a continuous cell wall amongst other characteristics.

Can Xenon help determine if the carbon traces in ancient rocks is biogenic or not?

The fingerprints of Ur, the earliest supercontinent, are in the Bastar Craton in India.

Hadean:

The energy budget and structure of the earth get modeled during and after the Thea impact.

Origin of Life:

Bacterial gene duplicates are more common in eukaryotes than expected.

Is there a relation between hydrothermal chemistry and the origin of cellular life?

META:

Archaea's biochemistry may give hints as to ancient ocean temperature.

A large virus may have helped make the first eukaryote allow endosymbiosis allowing for the evolution of photosynthesis in eukaryotes.

Pondering the Precambrian #28

Proterozoic:

NeoProterozoic:

Ediacaran:

A cyanobacteria normally associated with the Phanerozoic has been found in Ediacaran deposits in China.

There was a significant shift in what the limiting nutrients were across the Ediacaran/Cambrian boundary.

How did the black shales form across the Ediacaran/Cambrian boundary?

Was the Sao Francisco Basin a restricted basin during the Ediacaran?

A section in China appears to be a record of the late Ediacaran glaciations, showing a cold, dry climate.

The Cathayasian block was attached to Gondwana since 630 million years ago.

The fate of an inland sea from during the Neoproterozoic gets discussed.

Evidence of the Milkanovich cycles is preserved in Ediacaran deposits.

Tubular fossils from the Weng'an Biota are algae, not metazoans.

Weng'an Biota also provides examples of preserved encysting of eukaryotes.

Cryogenian:

Could the banded iron formations of the Cryogenian be related to ocean acidification?

There is evidence of a less than complete snowball earth from China during the Marinoan Glaciation.

Cryogenian Period deposits of Datangpo Formation of China from the interglacial period between the Sturtian and Marinoan glaciations show a very stratified ocean.

The majority of the time, the NeoProterozoic oceans were anoxic and were supersaturated with dolomite.

Tonian:

Fungus fossils appear to have been found in Tonian (neoproterozoic) or Stenian (mesoproterozoic) deposits in Canada.

There appears to have been a paleorifting event during the Tonian of the Sao Francisco-Congo continent.

The Sognefjel complex appears to have formed in the Asgardian Sea during the early Tonian.

Did the Paleo-South China Ocean close during the Tonian?

MesoProterozoic:

The Eastern European Craton has a Mesoproterozoic signal.

The southern Grenville formation dates from Mesoproterozoic and is from purely Laurentian sources.

Reported stromatolites from a Stenian lake cannot be proven to be biogenic.

Paleoproterozoic:

600 million years of sedimentation is examined from the Paleoproterozoic of Lapland.

Statherian Period evolution of the Oolongbuluke terraine is explained.

In Brazil, the Sobreiro Formation appears to be from the Orosirian/Statherian boundary.

Archean:

There is evidence of retreating oceanic slab subduction from the NeoArchean of China.

Evidence from India suggests there was significant local variation in Archean ocean conditions.

The Caozhuang basin appears to be a case of sagduction.

Fossils from paleoarchean South Africa show bacteria dividing and they appear to be very similar to cyanobacteria Pleurocapsales.

Eoarchean stromatolites get examined.

Hadean:

Was the Earth covered in a lava ocean before Theia impacted and created the moon?

META:

What are the implications of a hotter mantle, but colder subduction during the Precambrian?

Pondering the Precambrian #27

Proterozoic:

NeoProterozoic:

Did a massive volcanic eruption trigger the Gaskiers Glaciation?

Deposits from British Columbia may be evidence of deep sea conditions just prior to the Gaskiers Glaciation.

Fossil fats from the Cryogenian may actually be from algae instead of sponges.

Amoebozoa diversified earlier than expected during the Tonian 750 million years ago.

How were banded iron formations created in Egypt from the NeoProterozoic?

Was the Cambrian Explosion really that big a deal? Or did it really originate in the Ediacaran?

First record of carbonates with spherulites and cone-in-cone structures from the Ediacaran of Norway has been found.

MesoProterozoic:

The Yili Block was likely located in the NW margin of the supercontinent Rodinia.

PaleoProterozoic:

The apparent cyclical deposition of the Dales Gorge Member banded iron formation appears to be related to sea level rise and fall or tectonic activity.

The Vempalle Formation dolomites of India appear to have more in common with Phanerozoic carbonates than Proterozoic ones.

There's a sedimentation record from 2.27 BYA to 1.96 BYA in West Africa with evidence of volcanic ash and activity in the layers.

The first drillings into the Temagami Anomaly have uncovered potential links to the Sudbury Impact.

The Francevillian Biota of Rhyacian Gabon seems to have had something able to move.  Scientists have found evidence of trackways from shallow, oxygenated waters.

Archean:

Evidence from Mauritania suggests the Archean geophysics were as complicated as today.

Evidence of a breakup of a continent from the Archean.

There appears to be evidence of major crustal growth circa 2.6 BYA and 3.2 BYA.

There is evidence plate tectonics were active, despite prior theory, during the Archean.

MesoArchean:

There is evidence of a continental margin at the tail end of the MesoArchean in North China.

A subduction zone has been found from the MesoArchean/NeoArchean boundary.

Evidence of a continental rift was found in Hainan, China from the MesoArchean.

There is evidence of ephemeral oxygen oases in the Mesoarchean Ocean.

PaleoArchean:

South African barite deposits were not laid down in a marine environment, but from a spring.

Life was thriving during the paleoarchean 3.5 billion years ago.

EoArchean:

How the first continents formed in the EoArchean.

Hadean:

Was the Theia impact the reason for the heterogeneity of Earth's crust?

Origin of Life:

Was the repeated drying and wetting cycle of the margin of water the source of energy for the original polymerization of amino acids et al?

Did hydrogen peroxide play a crucial role in the origin of life?

Pluripotency and the origin of multicellular life.

Could the RNA world hypothesized never have existed?

Shallow pools of water might have been the original location for the origin of life, not the sea.

Pondering the Precambrian #26

Proterozoic:

NeoProterozoic:

The Earth's magnetic field was 10% of what it is today during the Ediacaran and the Earth's solid core may date from that period.

Evidence from Murmansk supports the weak magnetic field hypothesis during the Proterozoic.

Trace fossils from the Ediacaran have been found in Brittany, France.

Ediacaran environmental changes are recorded in Brazil.

The iodine content of the the Doushanto deposits of the Ediacaran.

Microorganisms are the source of organic carbon found in Sichuan from the Ediacaran into the Cambrian. 

It appears Cloudina and other tubular organisms from the terminal Ediacaran appear to have reproduced asexually.

There is evidence of hydrothermal activity altering various deposits during the Ediacaran.

Evidence of the breakup of Rodinia to the accretion of Gondwana in the Ediacaran from Paraguay.

A new biomarker has been found from the Cryogenian that hints at how complex life evolved after the Snowball Earth.

There was a deep marine organic reservoir in the Cryogenian.

Starting in the Cryogenian until the start of the Carboniferous, there was significant lack of impacts.  There might be evidence of the Snowball Earth via a global wiping of the impact craters from before that point, too.

Could the Great Noncomformity be due to the Snowball Earth?

The Great Noncomformity represents a 200to 300 million year gap in the depositional history of the world according to evidence from the North China Craton.

There are graphite particles in Cryogenian deposits of Nantuo.

Manganese ore deposits in South China were formed in the interglacial between the Sturtian and Marinoan glacials by microbial activity.

Is hydrothermal activity from the Tonian of the Western Australian Craton evidence of the breakup of Rodinia?

Mesoproterozoic:

Eukaryotes diversified earlier than previously thought, starting in the Ectasian.

Paleoproterozoic:

There was a 30 degree shift in the mafic dyke swarms during the Paleoproterozoic.

The surface conditions of at the start of the Great Oxygenation Event were anoxic.

There is evidence from the Yangtze Block that contradicts the hypothesis that there was a shutdown of plate tectonics during the PaleoProterozoic.

Archean:

A coupled crust/mantle formed before 2.5 billion years ago.

Evidence from the MesoArchean to the Paleoproterozoic of Norway show how the continents were built up.

More evidence of episodic crust growth starting in the MesoArchean.

There may be EoArchean deposits in the North China craton.

Sarmatia, Pilbara, and Kaapvaal Cratons were all part of the single supercontinent Vaalbara.

There's no evidence of pre 3.95 billion year old fossils.

Hadean:

Did the impact with Theia provide the volatiles the Earth needed for life?

Did asteroid impacts have a central role in the formation of the original continents?

META:

There is a 600 million year superocean cycle modulating a longer supercontinent.

Could sulfur dioxide have helped with the start of prebiotic carbohydrates?

There are biochemical hints that the last common universal ancestor - the last life form from which everything alive is descended - was not a hyperthermophile.

Reconstruction the Last Eukaryote Common Ancestor's genome to understand the evolution from the First Eukaryote Common Ancestor to the LECA.

Chunks of RNA can be formed prebioticly.

Studying algae suggest eukaryotes have received numerous DNA additions from bacteria.

Pondering the Precambrian #11

Proterozoic:

NeoProterozoic:

The problematic Orbisiana fossil from the Ediacaran of Russia is reevaluated.

Ediacaran life formed complex ecological communities.

Dickinsonia is confirmed to be an Ediacaran animals.  In fossils from the White Sea, molecular traces of steroids were found.

There is more evidence of sponges being present on the sea floor during the Cryogenian.

Precambrian Research is doing a special issue on the Cryogenian and especially the Tonian/Cryogenian transition.

There is evidence of the Rodinia supercontinent breakup during the Tonian.

MesoProtoerozoic:

From during the Stenian, there is evidence of an intracontinental rift forming in Australia.

There is evidence the shallow waters of the MesoProterozoic were anoxic.

Where and when did the PaleoAsian Ocean form?   Another view.

PaleoProterozoic:

There is evidence Africa and Brazil were part of the Congo-Sao Francisco continent during the PaleoProterozoic and of mountain building from that timeframe.

Carbonatite found in China gives a precise time for the beginning of the breakup of the Columbia supercontinent during the Orosirian.

Archean:

There is evidence of sulfur munching microbes from NeoArchean hydrothermal system ~2.7 billion years ago.

The oldest known paleosols - soil fossils - may have been found and date from the EoArchean.

The trace fossils from the PaleoArchean attributed to life might NOT be anything of the sort.

Hadean:

Hadean into the Archean, Earth seems to have lost an ocean's worth of water.  Or at least the hydrogen from it.

There is evidence suggesting there might have been banded iron formations and chert deposits laid down in the Hadean.

Do plate tectonics date from the Hadean?!

Origin of Life:

A new timeline has been proposed for the evolution of life.

What was the origin of life in the Hadean to PaleoArchean?

What was the time period for the origin of life?

Aging may have been a fundamental property of life and dates from life's actual origin..

Could formamide been the original prebiotic solvent?

Did liquid crystals help with the formation of life?

The ancestral eukaryote is slowly being understood.

Ws early photosynthetic life on Earth purple?

Pondering the Precambrian #9

Proterozoic:

There is evidence from the Proterozoic that Earth's day was 18 hours long.

NeoProterozoic:

Ediacaran:

The evolution of biological productivity and primary producers across the Ediacaran/Cambrian boundary

The Hüttenberg Anomaly appears to have been evidence of the Ediacaran oxygenation event.

Oxygenation variations in the atmosphere and shallow waters in the Yangzte platform.

Did anoxia kill off the Ediacaran benthic communities?

The Doushantuo fossils from China get examined closer.

Bilateral animal trackways and metazoan burrows have been discovered in the Ediacaran Dengying formation.

Two new disc critters from the Ediacaran have been found.  One was named for Sir David Attenborough.  The other for Barrack Obama.

Why did rangeomorphs grew so large during the Ediacaran?

What caused the mass extinction of the Ediacaran Biota?

Cryogenian:

Argonite fans were present in the bottom sediments during the Marinoan Glaciation.

Tonian:

India and Suixian sedimentary group were connected and either were on the margin of the supercontinent of Rodinia or were on a separate plate.

MesoProterozoic:

Evidence of an island arc from the Calymmian has been found.

PaleoProterozoic:

Australia was not connected to Laurentia from 1.8 gya to 1.65 gya during the Nuna/Columbia supercontinet.

During a continent breakup, there appears to have been enhanced terrestrial input into Chinese carbonates.

There is evidence of oceanic crust subduction from China.

During the Siderian, continental microbes and their 'crusts' on rocks might have helped seed the oceans with nitrogen.

Archean:

NeoArchean:

Continents rising above the ocean changed the climate and environment, permanently, on earth.  

Did the dawn of plate tectonics trigger a NeoArchean Snowball Earth episode?

The interplay between crustal arcs and mantle plumes was important in the Archean.

There is no support of wide spread increases in oxygen in shallow waters from South Africa leading up to the Great Oxygenation Event.

MesoArchean:

There might be evidence of two separate turns of the Wilson Cycles in Chinese deposits during the Archean.

Yet, it seems crustal production was periodic prior to 2.7 gya.

PaleoArchean:

Evidence of microbial mats was found from the PaleoArchean.

Hadean:

The Earth might have been able to form a high silica crust during the Hadean, less than 350 million years after its formation.

Origin of Life:

How primordial life might have replicated itself.

Experimental Paleontology:

Fish eggs were used to test how precambrian embryos might have been silicified.  

Pondering the Precambrian #8

Proterozoic:

NeoProterozoic:

Some paleosols found in the Baltic were formed during the NeoProterozoic during an extended weathering event.

What came first?  High levels oxygen in the atmosphere or animals?  Animals.

Evidence encrusting became an ability of Metazoans during the Ediacaran.

Were the Beltanelliformis fossils of the Ediacaran just cyanobacteria colonies?

There is evidence of carbon isotopic excursions from the Ediacaran Bilara Group in India.

The Ediacaran carbon isotopic excursions in South China are associated with phosphite upwellings.

There is evidence of the Ediacaran glaciations from Morocco.

Evidence of the transition from anoxic oceanic conditions during the Cryogenian to the oxic in the Ediacaran as well as the great meltwater from the Cryogenian snowball has been found.

Evidence of the mixing of glacial waters with the anoxic ocean has been found in California from during the Cryogenian.

There appears to have been an oxygen spike during the early Tonian.

There are banded iron formations in early NeoProterozoic Hainan, China.

Can Nanosims be useful in examining organic walled microfossils from the NeoProterozoic?

It appears something was burrowing in the late Ediacaran of Mongolia, much earlier than previously thought.


Exploring the effect of oxygen on the formation of haze in the NeoProterozoic atmosphere.

MesoProterozoic:

The Upper Vindhyans formation in India dates from the Late MesoProterozoic.

Evidence from China suggests the oceans of the Ectasian were anoxic to suboxic.

There is also evidence of Ectasian/Calymmian boundary oceans having banded iron formations.

Evidence from China also suggests active hydrothermal systems put a lot of iron into the shallow seas during the break up of the Columbia supercontinent.

Does photosynthesis in modern plants date to the Stenian?

PaleoProterozoic:

It appears the oceans of the Siderian become oxygenated 250 million years BEFORE the atmosphere did.

There is evidence a snowball earth scenario unfolded during the Siderian as well.

It looks like there is evidence of a tsunami or a storm from the PaleoProterozoic.

Organic remains in granular iron formations suggest they might be biological in origin.

Paleoproterozoic stromatolites from South Africa were formed in a restricted basin.

Evidence of the Great Oxygenation Event comes from rock salt from Russia.

Archean:

The Late Heavy Bombardment is being questioned.

By the end of the NeoArchean, the first modern continents had formed.

There may be volcanogenic pseudofossils in the PaleoArchean formation at Pilbara.

There's evidence of an oceanic plateau from the Archean in Nunavut, Canada.

University of Tuebingen in Germany and the Chinese Academy of Sciences in Beijing experimentally attempted to recreate the ocean of the Archean to explain its banded iron formations.

When did life originate?  At the dawn of the Archean?  Or later?

Hadean:

What the nitrogen cycle of a prebiotic Earth might have been like.

META:

Chromium isotopes can give false data for oxygen levels.

Chemists have found a plausible formula for the origin of life in Prebiotic earth.

Argnine might have played an important role in the origin of life.

A new origin of life hypothesis has been forwarded.

Did volcanic eruptions spew enough sulfur dioxide to kick off the origin of life?

Manganese oxides can produce pseudofossils.

Constraining the Early Earth's climate and oceanic acidity.

When was the earliest life could have originated?

Did ice in the earliest Earth's ocean help facilitate the origin of life?

Oceanic tides may greatly decrease when supercontinents form.

Hadean Earth Art

Scientists one Step Closer to Replicating the Primordial RNA World

Scientists at The Scripps Research Institute (TSRI) have taken a big step toward the laboratory re-creation of the "RNA world," which is generally believed to have preceded modern life forms based on DNA and proteins.

"This is probably the first time some of these complex RNA molecules have been synthesized with a ribozyme [a special RNA enzyme] since the end of the RNA world four billion years ago," said TSRI Professor Gerald F. Joyce, the senior author of the study.

The results from the study, reported this week in the online Early Edition of the Proceedings of the National Academy of Sciences, show the scientists have succeeded in creating a ribozyme that can basically serve both to amplify genetic information and to generate functional molecules.

The new ribozyme can replicate short lengths of RNA efficiently and perform transcription on even longer RNAs to make functional RNA molecules with complex structures--coming close to what scientists imagine in terms of an RNA replicator that could have supported life before modern biology, where protein enzymes now handle gene replication and transcription.

link.

Was an Impact the Source of a Hadrean Zircon?

Differentiated impact melt sheets may be a potential source of Hadean detrital zircon

Authors:

Kenny et al

Abstract:

Constraining the origin and history of very ancient detrital zircons has unique potential for furthering our knowledge of Earth's very early crust and Hadean geodynamics. Previous applications of the Ti-in-zircon thermometer to >4 Ga zircons have identified a population with relatively low crystallization temperatures (Tzirxtln) of ∼685 °C. This could possibly indicate wet minimum-melting conditions producing granitic melts, implying very different Hadean terrestrial geology from that of other rocky planets. Here we report the first comprehensive ion microprobe study of zircons from a transect through the differentiated Sudbury impact melt sheet (Ontario, Canada). The new zircon Ti results and corresponding Tzirxtln fully overlap with those of the Hadean zircon population. Previous studies that measured Ti in impact melt sheet zircons did not find this wide range because they analyzed samples only from a restricted portion of the melt sheet and because they used laser ablation analyses that can overestimate true Ti content. It is important to note that internal differentiation of the impact melt is likely a prerequisite for the observed low Tzirxtln in zircons from the most evolved rocks. On Earth, melt sheet differentiation is strongest in subaqueous impact basins. Thus, not all Hadean detrital zircon with low Ti necessarily formed during melting at plate boundaries, but at least some could also have crystallized in melt sheets caused by intense meteorite bombardment of the early, hydrosphere-covered protocrust.

Evidence of Biological Traces in Hadean Eon Zircons

Pondering the Precambrian #3

Proterozoic:

NeoProterozoic:

The Royal Tyrrell Museum has a lecture on the Ediacaran.

There is stronger evidence for the biomarkers for sponges being present starting in the Cryogenian.

MesoProterozoic:

The shallow seawaters of the Calymmian MesoProterozoic were very hypoxic, showing evidence of having .1% of the current oxygen in seawater.

PaleoProterozoic:

There is evidence of intracontinental rifting from China during the Rhyacian Paleoproterozoic.

Was there a 'Mawson continent' during the Paleoproterozoic?

Archean:

The SETI Institute has a lecture on volcanism during the Archean.

PaleoArchean:

At least part of the trace fossils from Australia are pseudofossils (not real fossils).

EoArchean:

There is evidence of atmospheric oxygen from the EoArchean, 800 million years earlier than ever detected (or suspected) before.

Hadean:

In an almost extraordinary claim, the Siberian Craton may have bits of the crust from the Hadean!

Penciling in Details of the Hadean

Penciling in details of the Hadean

Author:

House

Abstract:

Some truly remarkable graphite is described by Bell et al. in PNAS (1). Graphite is, of course, the same material as found in pencil tips or in the anode of lithium ion batteries. Graphite is, however, also a very common material in Earth Science, and is often the form of carbon found in very old fossils that have been subjected to substantial heat. The graphite described in the Bell et al. article is remarkable because it is exceptionally old, dating to the Hadean eon. Officially, the Hadean is defined as the time period from the formation of the Earth until 4 billion y ago. Until recently, this has been a seemingly convenient definition, leaving it as the geological eon without a rock record on Earth. Over the past quarter century, however, the discovery and exploration of detrital zircon minerals from the Jack Hills conglomerates of Western Australia (2) have provided a new window into this early time. Jack Hills zircons crystallized in magma chambers at various times as far back as 4.4 billion y ago (3, 4). So far, these zircons and their inclusions are currently our only tangible record of the first half a billion years of Earth history. Based in part on the extreme age of some of these zircon minerals, along with similarly old age dates for a Martian meteorite (5), the Planetary Science and Earth Science communities now appreciate that planets form and cool rather quickly (6). No longer is the Hadean just a placeholder on our timelines between the formation of the Earth and the oldest known rocks

Plate Tectonics Were Initiated by Mantle Plumes

Plate tectonics on the Earth triggered by plume-induced subduction initiation

Authors:

Gerya et al

Abstract:

Scientific theories of how subduction and plate tectonics began on Earth—and what the tectonic structure of Earth was before this—remain enigmatic and contentious. Understanding viable scenarios for the onset of subduction and plate tectonics is hampered by the fact that subduction initiation processes must have been markedly different before the onset of global plate tectonics because most present-day subduction initiation mechanisms require acting plate forces and existing zones of lithospheric weakness, which are both consequences of plate tectonics. However, plume-induced subduction initiation could have started the first subduction zone without the help of plate tectonics. Here, we test this mechanism using high-resolution three-dimensional numerical thermomechanical modelling. We demonstrate that three key physical factors combine to trigger self-sustained subduction: (1) a strong, negatively buoyant oceanic lithosphere; (2) focused magmatic weakening and thinning of lithosphere above the plume; and (3) lubrication of the slab interface by hydrated crust. We also show that plume-induced subduction could only have been feasible in the hotter early Earth for old oceanic plates. In contrast, younger plates favoured episodic lithospheric drips rather than self-sustained subduction and global plate tectonics.

Did the Late Heavy Bombardment Destroy the Hadean Crust?

Excavation and Melting of the Hadean Continental Crust by Late Heavy Bombardment

Authors:

Shibaike et al

Abstract:

No Hadean rocks have ever been found on Earth's surface except for zircons---evidence of continental crust, suggesting that Hadean continental crust existed but later disappeared. One hypothesis for the disappearance of the continental crust is excavation/melting by the Late Heavy Bombardment (LHB), a concentration of impacts in the last phase of the Hadean eon. In this paper, we calculate the effects of LHB on Hadean continental crust in order to investigate this hypothesis. Approximating the size-frequency distribution of the impacts by a power-law scaling with an exponent {\alpha} as a parameter, we have derived semi-analytical expressions for the effects of LHB impacts. We calculated the total excavation/melting volume and area affected by the LHB from two constraints of LHB on the moon, the size of the largest basin during LHB, and the density of craters larger than 20 km. We also investigated the effects of the value of {\alpha}. Our results show that LHB does not excavate/melt all of Hadean continental crust directly, but over 70% of the Earth's surface area can be covered by subsequent melts in a broad range of {\alpha}. If there have been no overturns of the continental crust until today, LHB could be responsible for the absence of Hadean rocks because most of Hadean continental crust is not be exposed on the Earth's surface in this case.

Discovery of Hadean Crustal Materials in SW China

Discovery of Hadean–Mesoarchean crustal materials in the northern Sibumasu block and its significance for Gondwana reconstruction

Authors:

Li et al

Abstract:

The micro-continental blocks in SE Asia are thought to be derived from the East Gondwana which has a basement as old as Hadean–Mesoarchean. However, such old crustal materials have not been found anywhere in SE Asia. In this paper, we report the occurrence of the Hadean–Mesoarchean crustal materials in the northern Sibumasu block, SW China. Our finding is based on inherited zircon U–Pb ages and Hf isotope model ages of co-magmatic zircon crystals from early-Paleozoic S-type granitoids in the northernmost Sibumasu. LA-ICP-MS zircon U–Pb isotopic analysis reveals that some S-type granitoids in this region formed between 468 Ma and 447 Ma. These rocks are strongly peraluminous, with high A/CNK ratios > 1.2 and normative corundum content > 2 wt%, and have low CaO/Na2O ratios less than 0.3 which indicates that they formed by anatexis of metapelitic crustal rocks. The ca. 470–450 Ma S-type granitoids contain inherited zircon crystals as old as Mesoarchean (∼3.1 Ga). The ɛHf(t) values of zircon crystallized from the magmas of these rocks vary from −49 to +16, with major peaks approximately at −46, −35 and −27. The corresponding model ages for the formation of the source crust are ∼4.39 Ga, ∼3.62 Ga and ∼3.12 Ga. This, together with the discovery of ∼3.1 Ga inherited zircon in the granitoids, indicates that the northern Sibumasu block has Hadean–Mesoarchean crustal materials. A Gondwana-wide comparison of crustal formation time data reveals that these Hadean–Mesoarchean crustal materials show similar age distribution with the crusts of the Pilbara and Yilgarn Cratons, Western Australia. Their derivation analysis provides a new line of evidence for the majority view that the Sibumasu block was attached to NW Australia before its breakup from Gondwana.

Did Life Originate During the Hadean Prior to the end of the Late Heavy Bombardment?

UCLA geochemists have found evidence that life likely existed on Earth at least 4.1 billion years ago -- 300 million years earlier than previous research suggested. The discovery indicates that life may have begun shortly after the planet formed 4.54 billion years ago.

The research is published today in the online early edition of the journal Proceedings of the National Academy of Sciences.

"Twenty years ago, this would have been heretical; finding evidence of life 3.8 billion years ago was shocking," said Mark Harrison, co-author of the research and a professor of geochemistry at UCLA.

"Life on Earth may have started almost instantaneously," added Harrison, a member of the National Academy of Sciences. "With the right ingredients, life seems to form very quickly."

The new research suggests that life existed prior to the massive bombardment of the inner solar system that formed the moon's large craters 3.9 billion years ago.

"If all life on Earth died during this bombardment, which some scientists have argued, then life must have restarted quickly," said Patrick Boehnke, a co-author of the research and a graduate student in Harrison's laboratory.

Scientists had long believed the Earth was dry and desolate during that time period. Harrison's research -- including a 2008 study in Nature he co-authored with Craig Manning, a professor of geology and geochemistry at UCLA, and former UCLA graduate student Michelle Hopkins -- is proving otherwise.

"The early Earth certainly wasn't a hellish, dry, boiling planet; we see absolutely no evidence for that," Harrison said. "The planet was probably much more like it is today than previously thought."

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Microbes Caused the RIse of the First MicroContinents?

Microbes, Mineral Evolution, and the Rise of Microcontinents—Origin and Coevolution of Life with Early Earth

Authors:

Grosch et al

Abstract:

Earth is the most mineralogically diverse planet in our solar system, the direct consequence of a coevolving geosphere and biosphere. We consider the possibility that a microbial biosphere originated and thrived in the early Hadean-Archean Earth subseafloor environment, with fundamental consequences for the complex evolution and habitability of our planet. In this hypothesis paper, we explore possible venues for the origin of life and the direct consequences of microbially mediated, low-temperature hydrothermal alteration of the early oceanic lithosphere. We hypothesize that subsurface fluid-rock-microbe interactions resulted in more efficient hydration of the early oceanic crust, which in turn promoted bulk melting to produce the first evolved fragments of felsic crust. These evolved magmas most likely included sialic or tonalitic sheets, felsic volcaniclastics, and minor rhyolitic intrusions emplaced in an Iceland-type extensional setting as the earliest microcontinents. With the further development of proto-tectonic processes, these buoyant felsic crustal fragments formed the nucleus of intra-oceanic tonalite-trondhjemite-granitoid (TTG) island arcs. Thus microbes, by facilitating extensive hydrothermal alteration of the earliest oceanic crust through bioalteration, promoted mineral diversification and may have been early architects of surface environments and microcontinents on young Earth. We explore how the possible onset of subseafloor fluid-rock-microbe interactions on early Earth accelerated metavolcanic clay mineral formation, crustal melting, and subsequent metamorphic mineral evolution. We also consider environmental factors supporting this earliest step in geosphere-biosphere coevolution and the implications for habitability and mineral evolution on other rocky planets, such as Mars.

Earth has had a Magnetic Field Since the Hadean

A Hadean to Paleoarchean geodynamo recorded by single zircon crystals

Authors:

Tarduno et al

Abstract:

Knowing when the geodynamo started is important for understanding the evolution of the core, the atmosphere, and life on Earth. We report full-vector paleointensity measurements of Archean to Hadean zircons bearing magnetic inclusions from the Jack Hills conglomerate (Western Australia) to reconstruct the early geodynamo history. Data from zircons between 3.3 billion and 4.2 billion years old record magnetic fields varying between 1.0 and 0.12 times recent equatorial field strengths. A Hadean geomagnetic field requires a core-mantle heat flow exceeding the adiabatic value and is suggestive of plate tectonics and/or advective magmatic heat transport. The existence of a terrestrial magnetic field before the Late Heavy Bombardment is supported by terrestrial nitrogen isotopic evidence and implies that early atmospheric evolution on both Earth and Mars was regulated by dynamo behavior.