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 #39

Proterozoic:

NeoProterozoic:

Global microfossil changes across the Ediacaran/Cambrian are characterized.

A new method of characterizing oxygen availability across the Ediacaran/Cambrian boundary has been found.

The lack of attention to taphonomy can mislead about the late Ediacaran fossils.

Data from Argentina covers the Ediacaran's oxygenation event.

Simulations of Ernettia suggest it was a filter feeder and fed better in groups.

Has there been a case of lateral gene transfer detected in bilaterians?

Ancient paralogies suggest jellyfish are a sister group to all other metazoans.

Green algae transitioned to macroscopic growth multiple times, but only as recently as the NeoProterozoic.

There is evidence of strange magmatism in the Sahara from the Ediacaran 580 million years ago.

An astronomical time scale for the middle/upper Doushantuo Formation has been established.

Braided rivers were not the rule prior to the evolution of plant life despite previous thought.

The Paleo Hunan Ocean was completely closed by 830 million years ago during the Tonian.

Evidence of two carbon excursions are detected in Tonian deposits in Namibia.

MesoProterozoic:

A new model suggests a sluggish, tepid mesoproterozoic ecosystem.

A very large igneous magmatic province has been found in South Africa from Stenian of South Africa.  These provinces are associated with mass extinctions like the Permian and Triassic/Jurassic.

An impact has been found in Scotland dating from the Mesoproterozoic.

Was anaerobic photosynthesis the reason for the delayed rise in oxygen in Earth's atmosphere?

PaleoProterozoic:

Iron stones were laid down by iron oxidizing bacteria during the Statherian.

There is evidence of deep subduction from North China from the Paleoproterozoic.

There is also evidence of a significant back arc continental collision during the Orosirian in the North China Craton.

There is evidence, according to Retallack, of macroscopic terrestrial life from the Orosirian.

The shape of the Dhala Crater in India from the Rhyacian is reconstructed.

Paleoproterozoic dolomites shed some light on the evolution of marine chemistry.

Archean:

The early Earth's oceans may not have been as hot as originally thought.

Compared to later granites, Archean granites had relatively unstable compositions.

Archean sulfur isotopes from Australia's Fraser Zone have unexplained ratios and amounts.

Did the subduction of the oceanic basins take place during the mesoarchean?

Could continents have existed from the dawn of the Archean, during the Eoarchean?

Eoarchean hydrothermal vent boron deposits give some insight to the origin of life.

Origin of Life:

Peptides can form without amino acids.

Could microscopic bubbles (interfaces) have helped kickstart life?

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 #25

Proterozoic:

NeoProterozoic:

Cobalt deposits may be 150 million years younger than previously thought and due to an orogenic event.

There's evidence suggesting scavenging was the origin of predation during the Ediacaran.

There's evidence of shifting from continental collision to a subduction in Africa during the Ediacaran.

There were very diverse microfossils from the Ediacaran Doushantuo Formation.

The fossilization method of the Ediacaran gets examined for the earliest metazoans.

Fossils from the Ediacaran site at Nilpena, Australia are biological snapshots of benthic communities.

Ediacaran discoid fossils from the Anti-Atlas Mountains in Africa have been found.

In the early Ediacaran ocean, there seems to have been a global zinc signature.

Did the complex forms of the Ediacaran arise in the benthic depths of the ocean because there were stable temperatures?

In China, the carbonate caps suggest a oxygen recovery after the Marinoan Glaciation ended.

The oxygen isotopes from the Cryogenian meteoric water are similar to today's.

A group attempts to model the global temperatures from the Tonian to the present.

MesoProterozoic:

Fossils from Brazil suggest two different microbial habitats from the Stenian at the site.

There is evidence of oxygenated lakes 1.1 billion years ago during the Stenian.

There is evidence of oxygenation in the form of red beds that were created during an orogeny around the Stenian/Ectasian boundary.

PaleoProterozoic:

Statherian microfossils from China suggest eukaryotes were moderately diverse by that point in time.

Evidence of the Huronian Glaciation has been discovered in China.  This may have been the first time a Snowball Earth scenario took place.

Phosphorite deposits appear to have come from a microbial reef in the Siderian of Australia.

Archean:

Features from 2.7 billion year old stromatolite formations hint at the presence of oxygen.

The is evidence of a shift from vertical to horizontal plate tectonics in the Archean.

During the Mesoarchean the bottom waters of the ocean appear to have been anoxic.

There appears to have been a cryptic craton core that emerged in the Paleoarchean.

Aerobic photosynthesis might have arisen 3.5 billion years ago during the Paleoarchean.

Origin of Life:

Abiotic amino acids from the Earth's mantle have been observed for the first time.

Are liquid crystal matrices an analog to the early protocells?

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 #10

NeoProterozoic:

The Ediacaran's Palaeopascichnus linearis appears to be the oldest macroscopic organism.

Exceptinal preservation of biomarkers was found in Ediacaran deposits from the Eastern European Craton.

The paleoenvironmental change gets examined leading up to the Gaskiers Glaciation in the Ediacaran.

The interglacial timeframe in the Cryogenian appears to should anoxic marine waters in South China.

The end of the Cryogenian Sturtian Glaciation according to new dating techniques supports a global and rapid deglaciation consistent with the snowball earth scenario.

At the dawn of the Sturtian glaciation during the Cryogenian, solar activity left no sign of any change.

Stromatoveris appears to be a survivor from the Ediacaran into the Cambrian.

Mesoproterozoic:

During the Stenian, the marine ecosystems were dominated by bacteria.

There is evidence of increased, but still limited biological productivity from the Ectasian/Calymmian boundary in Canada.

Paleoproterozoic:

There is evidence in from an Orosirian lake in Russia, that methanotrophic and autophototrophic biomes lived in the same body of water.

Orosirian micrometer fossils were identified using laser ablation mass spectrometry.

Researchers attempted to model the GOE atmosphere and had an interesting result regarding methane.

Evidence from the Boolgeeda Iron Formation in Australia suggests shallow water oxygenation took place while the iron banded formations were being deposited.

The Kaapvaal Craton shows evidence of subduction at the Archean/PaleoProterozoic Boundary.

Archean:

Shallow waters in South Africa just prior to the Great Oxygenation Event were still anoxic.

The disappearance of certain sulfur compounds appears to make a good proxy for the rise of oxygen in the Archean atmosphere.

There seems to have been intermittent surface ocean oxygenation prior to the Great Oxygenation Event during the NeoArchean.

There is evidence of continental collisions and subduction from the MesoArchean.

There is evidence of bacterial mats inhabiting terrestrial environments during the late PaleoArchean.

There is also evidence of bacterial speciation from the PaleoArchean deposits of Pilbara, Australia.

The Strelley Pool micro fossils from the PaleoArchean appear to be biological.

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.

Pondering the Precambrian #7

Proterozoic:

NeoProterzoic:

The Tarim Craton may have been connected to the North India Block rather than Australia within the supercontinent of Rodinia during the Tonian.

Has evidence of mountain building during the Tonian been found in Scotland?

The Tonian/Cryogenian transition seems to have been located in Svalbard.

How complete is the evidence of glaciations during the Cryogenian in Scotland?

How oxygenated was the ocean between the Snowball Earth episodes?

Caution with carbon-13 shifts are urged in Cryogenian deposits as they are deposit dependent.

Evidence of hydrothermal modification of a dolostone during the Marinoan Glaciations.

Was there a delayed oxygenation of the oceans from the Cryogenian to the Ediacaran?

Evidence from Mongolia's 540 million year old Khesen formation documents the rise of animals.

Evidence that Ediacaran Parvancorina was motile and could sense benthic currents.

Were there constant anoxic bottom waters during the Ediacaran?

Cyanobacterial-algal crusts have been found from Ediacaran paleosols.

MesoProterozoic:

Cyanobacterial microfossils are examined from Calymmian China.

Were tellurium and selenium weathered from sandstones into the Mesoproterozoic oceans?

PaleoProterozoic:

Biosignatures have been found for eukaryotes from Statherian China.

There is evidence of an impact in India during the Siderian.

Was there a subduction cessation during the Siderian in China?

More evidence of warm subduction during the Orosirian from Cameroon.

Was the Great Oxygenation Event really an abiotic process?!

There appears to have been gradual oxygenation in the oceans (in some cases) just prior to the GOE.

A large igneous province is detected from India from the Rhyacian.

Was the early biosphere nutrient limited?

Archean:

Evidence from China, specifically the North China Craton, about the composition of NeoArchean sea water.

Inland lakes appear to have fostered the diversification of microbial life during the MesoArchean.

The oldest known paleosols (fossil soil) date from the PaleoArchean (3.46 billion years ago) and originate in Australia and may have formed from sulfuric acid weathering.

Could there be a problem with the cherts being used from the PaleoArchean to claim microbial life?

Or is there a definitive example of fossil life from the PaleoArchean?  Does that mean life is common in the universe?

Is some of Earth's magma ocean preserved in PaleoArchean rock?

META:

Exploring the Precambrian lithosphere of Zambia and Malawi.

The effect of paleoseawater chemistry on hydrothermal ridges.

Origin of Life:

The origin and diversification of the endosymbiont known as the mitochondria.

A new lineage of eukaryotes has given information on mitochondrial genome reduction.

Pondering the Precambrian #4

NeoProterozoic:

Ediacaran:

From Brazil, Ediacaran vase shaped fossils have been found.  is this the earliest known protist fossils yet?

How are the various frond critters of the Ediacaran related to each other?

How did the Ediacaran critter Dickinsonia grow?

A mixed Cloudinia-Corumbella-Namacalathus assemblage shows increasing ecological complexity over the course of the Ediacaran.

Cryogenian:

Did a freshwater layer exist on the world's oceans and persist after the Snowball Earth episodes like the one in the Cryogenian?

As the Snowball Earth ended, how much oxygen weathering took place and what were the biotic impacts?

Tonian:

There was a huge Andes-like mountain range on the northwest of Rodinia that may have lasted for 100 million years during the Tonian 800 million years ago.

MesoProterozoic:

Wind patterns have been inferred from dunes from Calymmian Brazil.

The diversity of Eukaryote microfossils of Calymmian China is impressive.

PaleoProterozoic:

In Statherian China, there is evidence of a sillicified microbiota from the Dahongyu Formation.

The Sudbury Impact appears to have caused long lived volcanic eruptions during the Orosirian PaleoProterozoic.  Since it was one of 150 impacts within a relatively short period, combined with this above volcanism, it should be no surprise life didn't recover to take a second stab at complexity for a billion years.

The Sudbury Basin continued to have geothermal heat during the Huronian snowball earth.

Can the Rhyacian/Siderian Glaciations (huronian snowball earth) be dated based on subglacial hydrothermal activity?

Beginning in the Siderian, ancient carbon was subsumed into the Earth's mantle.

Did anaerobic oxygenic photosynthesis (read the paper) come about in cyanobacteria prior to modern aerobic photosynthesis?

During the Siderian, Earth had a hazy, methane filled atmosphere.

Did eukaryotes arise during the Siderian?

Archean:

Lenticular organisms from South Africa are related to the Pilbara forms.

Did life arise during the EoArchean WITHOUT using phosphate?

Fossils were found from the Eoarchean 3.77 billion years ago in Quebec, Canada.

How did the crust form?

Hadean:

The Earth probably began with a solid shell for a crust, like Mars.

META:

New branches have been found in Archaea.

Iron eating, methanogen organisms probably kept the Earth warm for its first 2 billion years.

Mineral self assembly was common in the early years of the Earth.

Ediacaran NeoProterozoic Skeletal Metazoan Cloudina was Separate From Other Ediacaran Lifeforms

Flexible and responsive growth strategy of the Ediacaran skeletal Cloudina from the Nama Group, Namibia

Authors:

Wood et al

Abstract:

The Ediacaran skeletal tubular putative metazoan Cloudina occurs globally in carbonate settings, which both provided lithified substrates and minimized the cost of skeletonization. Habitat and substrate preferences and the relationship of Cloudina to other metazoans have not been fully documented, so we know little as to its ecological demands or community dynamics. In situ Cloudina from the Nama Group, Namibia (ca. 550–541 Ma), formed mutually attached reefs composed of successive assemblages in shallow, high-energy environments, and also communities attached to either stromatolites in storm-influenced deep inner-ramp settings or thin microbial mats in lower-energy habitats. Each assemblage shows statistically distinct tube diameter cohorts, but in sum, Cloudina shows an exponential frequency distribution of diameter size. In reefs, we document a periodicity of size variation, where mean, minimum, and maximum tube diameters vary together and show a systematic increase toward the top of each assemblage. We conclude that most Nama Group Cloudina represent one ecologically generalist taxon with highly variable size, that size was environmentally mediated, and that Cloudina could respond rapidly to periodic environmental changes. While Nama Group skeletal metazoans coexisted with soft-bodied biota, there was no apparent ecological interaction, as they were segregated into lithified carbonate and non-lithified clastic microbial mat communities, respectively. We infer that ecological flexibility allowed Cloudina to form varied communities that colonized diverse carbonate substrates under low levels of interspecific substrate competition. This is in notable contrast to the earliest Cambrian skeletal epibenthos that formed biodiverse reef communities with specialist niche occupancy.

How Long did the Ediacaran NeoProterozoic Shuram Event Last?

Rock magnetic cyclostratigraphy of the Doushantuo Formation, South China and its implications for the duration of the Shuram carbon isotope excursion

Authors:

Gong et al

Abstract:

The Shuram excursion (SE), one of the largest-known negative carbon isotope anomalies, has been globally observed in Ediacaran rocks. Precisely determining the duration of the SE is pivotal to understanding its controversial origin. Here, we present a detailed paleomagnetic, rock magnetic, cyclostratigraphic and carbon isotopic study of the SE in the Doushantuo Formation at the Dongdahe section in eastern Yunnan Province, South China. Although paleomagnetic results likely show a late Mesozoic remagnetization, careful mineralogic analyses indicate that the rock magnetic cyclostratigraphy carried by detrital pseudo-single domain (SD) or small multidomain (MD) titanomagnetite grains faithfully records orbitally-forced climate cycles in the Ediacaran. Multi-taper method (MTM) spectral analysis of magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) series reveals significant spectral peaks at similar frequencies. Based on the ratios of their frequencies, these spectral peaks are assigned to a suite of Milankovitch cycles (long eccentricity, short eccentricity, obliquity and precession), yielding a sediment accumulation rate of 1.0 cm/kyr for the Doushantuo Formation. A 9.1 ± 1.0 Myr duration is indicated for the entire SE in South China. This result is in good agreement with independent estimates from North America and South Australia, thus supporting a primary origin for the SE. In combination with published geochronologic data, we suggest that the onset of the SE occurred at ca. 560 Ma, which provides a chronostratigraphic framework for evaluating the relationship between the SE and the evolution of metazoans in Ediacaran time.

What Kind of Asteroids Impacted the Earth During the PaleoProterozoic?

Chromium isotope evidence in ejecta deposits for the nature of Paleoproterozoic impactors

Authors:

Mougel et al

Abstract:

Non-mass dependent chromium isotopic signatures have been successfully used to determine the presence and identification of extra-terrestrial materials in terrestrial impact rocks. Paleoproterozoic spherule layers from Greenland (Graenseso) and Russia (Zaonega), as well as some distal ejecta deposits (Lake Superior region) from the Sudbury impact (1,849 +/- 0.3 Ma) event, have been analyzed for their Cr isotope compositions. Our results suggest that 1) these distal ejecta deposits are all of impact origin, 2) the Graenseso and Zaonega spherule layers contain a distinct carbonaceous chondrite component, and are possibly related to the same impact event, which could be Vredefort (2,023 +/- 4 Ma) or another not yet identified large impact event from that of similar age, and 3) the Sudbury ejecta record a complex meteoritic signature, which is different from the Graenseso and Zaonega spherule layers, and could indicate the impact of a heterogeneous chondritic body.

Ecological and Biological Shifts During the Late Ediacaran NeoProterozoic

Ediacaran distributions in space and time: testing assemblage concepts of earliest macroscopic body fossils

Authors:

Boag et al

Abstract:

The mid-late Ediacaran Period (∼579–541 Ma) is characterized by globally distributed marine soft-bodied organisms of unclear phylogenetic affinities colloquially called the “Ediacara biota.” Despite an absence of systematic agreement, previous workers have tested for underlying factors that may control the occurrence of Ediacaran macrofossils in space and time. Three taxonomically distinct “assemblages,” termed the Avalon, White Sea, and Nama, were identified and informally incorporated into Ediacaran biostratigraphy. After ∼15 years of new fossil discoveries and taxonomic revision, we retest the validity of these assemblages using a comprehensive database of Ediacaran macrofossil occurrences. Using multivariate analysis, we also test the degree to which taphonomy, time, and paleoenvironment explain the taxonomic composition of these assemblages. We find that: (1) the three assemblages remain distinct taxonomic groupings; (2) there is little support for a large-scale litho-taphonomic bias present in the Ediacaran; and (3) there is significant chronostratigraphic overlap between the taxonomically and geographically distinct Avalonian and White Sea assemblages ca. 560–557 Ma. Furthermore, both assemblages show narrow bathymetric ranges, reinforcing that they were paleoenvironmental—ecological biotopes and spatially restricted in marine settings. Meanwhile, the Nama assemblage appears to be a unique faunal stage, defined by a global loss of diversity, coincident with a noted expansion of bathymetrically unrestricted, long-ranging Ediacara taxa. These data reinforce that Ediacaran biodiversity and stratigraphic ranges of its representative taxa must first statistically account for varying likelihood of preservation at a local scale to ultimately aggregate the Ediacaran macrofossil record into a global biostratigraphic context.

Evidence of a Radical PaleoOcean Chemistry Change Circa 545 Million Years Ago From Russia

Demise of Ediacaran dolomitic seas marks widespread biomineralization on the Siberian Platform

Authors:

Wood et al

Abstract:

The trigger for biomineralization of metazoans in the terminal Ediacaran, ca. 550 Ma, has been suggested to be the rise of oxygenation or an increase in seawater Ca concentration, but geochemical and fossil data have not been fully integrated to demonstrate cause and effect. Here we combine the record of macrofossils with early marine carbonate cement distribution within a relative depth framework for terminal Ediacaran to Cambrian successions on the eastern Siberian Platform, Russia, to interrogate the evolution of seawater chemistry and biotic response. Prior to ca. 545 Ma, the presence of early marine ferroan dolomite cement suggests dominantly ferruginous anoxic "aragonite-dolomite seas," with a very shallow oxic chemocline that supported mainly soft-bodied macrobiota. After ca. 545 Ma, marine cements changed to aragonite and/or high-Mg calcite, and this coincides with the appearance of widespread aragonite and high-Mg calcite skeletal metazoans, suggesting a profound change in seawater chemistry to "aragonite seas" with a deeper chemocline. By early Cambrian Stage 3, the first marine low-Mg calcite cements appear, coincident with the first low-Mg calcite metazoan skeletons, suggesting a further shift to "calcite seas". We suggest that this evolution of seawater chemistry was caused by enhanced continental denudation that increased the input of Ca into oceans so progressively lowering Mg/Ca, which, combined with more widespread oxic conditions, facilitated the rise of skeletal animals and in turn influenced the evolution of skeletal mineralogy.

Is the Shuram Event Still Younger Than the 580 Million Years agoEdiacaran NeoProteorozoic Gaskiers Glaciation Though?

Silicified glendonites in the Ediacaran Doushantuo Formation (South China) and their potential paleoclimatic implications

Authors:

Wang et al

Abstract:

The Ediacaran Period is punctuated by the ca. 580 Ma Gaskiers glaciation in Newfoundland. However, paleoclimatic data are scarce in Ediacaran successions in South China, where abundant geochemical and paleobiological data are shaping current understanding of Ediacaran evolutionary and environmental history. Here, we report the occurrence of silicified glendonites in the Ediacaran Doushantuo Formation deposited in an inner-shelf environment on the South China block. Petrographic evidence suggests that these silicified glendonites are pseudomorphs after syndepositional or early authigenic ikaites formed at near-freezing temperatures. The glendonite-bearing stratigraphic interval is characterized by positive δ13C values. It predates both the negative δ13C excursion EN3 (widely believed to be an equivalent of the Shuram negative excursion) and excursion EN2. Although alternative interpretations may be possible, these glendonites may be related to and correlated with the Gaskiers glaciation. If confirmed, this correlation suggests that the Shuram event postdates the Gaskiers glaciation, thus having important implications for Ediacaran climate changes, carbon cycles, and biological evolution.

Could the mid Ediacaran Shuram Event be Significantly Older Than 551 Million Years Ago?

The stratigraphic complexity of the middle Ediacaran carbon isotopic record in the Yangtze Gorges area, South China, and its implications for the age and chemostratigraphic significance of the Shuram excursion

Authors:

Zhou et al

Abstract:

The middle Ediacaran Shuram excursion represents the most pronounced negative carbon isotopic shift in Earth history, and has been considered as evidence for a profound disturbance to the global carbon cycle and proposed as a key chemostratigraphic marker for Ediacaran stratigraphic subdivision and global correlation. Previous study has revealed a pronounced negative δ13C shift (EN3) in the upper Doushantuo Formation of South China, which has been interpreted as an equivalent of the Shuram excursion. Detailed δ13C investigation of multiple sections of the Ediacaran Doushantuo Formation around the Huangling Anticline, western Hubei Province, South China, indicates that the δ13C variation in the upper Doushantuo Formation is more complex than previously reported. In the western region of the Huangling anticline, a moderately positive δ13C excursion (here termed the Diaoyapo positive excursion) bisects two strongly negative δ13C excursions (here termed the Jiuqunao negative excursion and the younger Miaohe negative excursion), with a ∼551 Ma ash bed capping the Miaohe negative excursion. In the central region, there is only one negative δ13C excursion, whereas in the eastern region, the negative δ13C excursion is absent. The variable stratigraphic expression of these δ13C excursions is most parsimoniously interpreted as reflecting local facies variation, diagenesis, and/or a cryptic unconformity. The more complete but more complex δ13C chemostratigraphic record in the western region of Huangling Anticline implies that, depending on how this record is correlated with the Shuram excursion, the latter may be significantly older than 551 Ma if it does represent a global chemostratigraphic marker.