New atmospheric paleoclimate tool: Rock Salt

Rock salt holds the key to a paradigm shift

A macro shot of salt crystals taken in the Natural History Museum of Vienna. Image: Wikimedia
A macro shot of salt crystals taken in the Natural History Museum of Vienna. Image: Wikimedia

Boulder, Colo., USA – A team of international scientists from China, France, Scotland, United States and led by Canadian Professors Nigel Blamey and Uwe Brand of Brock University in southern Ontario made a scientific breakthrough by measuring the oxygen content of Earth’s ancient atmosphere. They discovered that gases trapped by halite (rock salt) during crystallization may contain atmospheric gases, among them oxygen.

Oxygen is a key component in determining the origin and evolution of higher life forms that ultimately made Earth’s land and sea their home. The gases in inclusion of halite represent direct measurements of the ancient atmosphere, and can be used to calculate the dissolved oxygen content of past seawater and lay out the requirements for the evolution of higher life forms in the shallow and deep ocean.

This discovery has applications beyond the origin of life, to evaluating salt units as depositories for hazardous waste material, to tracking atmospheric changes in carbon dioxide and methane with climate change, to pinpointing the genesis of economic metal deposits, and application of this important scientific discovery to the search for life on extraterrestrial bodies.


The paper: 

Paradigm shift in determining Neoproterozoic atmospheric oxygen

Nigel J.F. Blamey et al., Department of Earth Sciences, Brock University, 1812 Sir Isaac Brock Way, St Catharines, Ontario L2S 3A1, Canada. This article is OPEN ACCESS online athttp://geology.gsapubs.org/content/early/2016/07/08/G37937.1.abstract.

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July 16, 2016 3:32 pm

The big assumption here is that the halite inclusions are the same age as the enclosing rock. Maybe, maybe not.

Johnny Cuyana
Reply to  wryheat2
July 16, 2016 4:22 pm

wryheat2: agreed. that diagenesis … especially with a host characterized with such unstable mineralogy; she’s a tough cookie to understand!

Reply to  wryheat2
July 16, 2016 5:41 pm

I’m afraid the big assumption is that any crystal inclusions are stable over the course of geologic time. That’s the essential problem with data derived from ice cores also.
Gasses seek equilibrium and crystals are porous to varied degrees. Ice is particularly porous to carbon dioxide, which is known to migrate in water ice. Only recently have some more rational members of the paleo-science community recognized this and begun to make some attempt to account for it. Water ice is not a permanent sequestration of atmospheric gas.
It’s extremely likely, if not a down right certainty, the same can be said of sodium chloride.

higley7
Reply to  Bartleby
July 16, 2016 6:24 pm

Jaworowski, an established expert in ice cores, recognizes the traumatic conditions of ice core extraction, including micro fracturing and depressurization, and estimates that 30–50% of the gases in the cores is lost on the way to the surface.
His estimate explains two things. One is the relatively low CO2 seen in the ice core records, and the other, the smoothing out of the ups and downs. Ingenuously, this is interpreted by the IPCC, who thinks ice core CO2 measurements are absolute measurements of atmospheric CO2, as indicating that CO2 has always been very low and only in the last 65 years has it risen due to our CO2 emissions.
If you back calculate an additional 40% into the CO2 measurements, you end up with atmospheric CO2 being the same or higher than now, with the lows in the <300 ppm being very rare. At best, one has to admit/accept that ice core CO2 measurements are under-estimates and that they are significantly, about 40%, low.

Ian Macdonald
Reply to  Bartleby
July 16, 2016 10:18 pm

The LENR experiments, and also the process of hydrogen embrittlement of metals, have demonstrated that given time and sufficient pressure, small molecules can pass right through solids. It is therefore unreasonable to assume that over geological time,.’trapped’ gases in solids will remain unaltered.

Reply to  Bartleby
July 17, 2016 3:44 am

Bartleby,
In the case of CO2 and ice, that depends of temperature. There were theoretical migration speeds deduced from increased CO2 levels near remelt layers of relative “warm” (-20°C) coastal ice cores from Antarctica (Siple Dome) which show a migration at medium depth (~2.7 kyear) of around 10%, meaning that the resolution of ~20 years increased to ~22 years. At full depth, the migration decreased the resolution to 40 years.
See: http://catalogue.nla.gov.au/Record/3773250
No big deal at all. For the much colder (-40°C) inland ice cores like Vostok (420 kyear) and Dome C (800 kyear), there is practically no migration even not over 800,000 years.
If there was appreciable migration, the interglacial peaks each some 100 kyear apart would flatten over time, but the T-CO2 ratio remains the same over the full length of the ice cores. Moreover, if there was migration of the peaks from the interglacial to the full glacial periods, that also means that during glacial periods the CO2 levels were (far) below the measured 180 ppmv, which effectively would have killed all C3 plants…
Migration depends of the effective diameter of the atom/molecule and the pore diameter of the materials involved. It is known that atomic hydrogen does migrate through steel at high temperatures. When there are small air inclusions in the metal, H2 molecules are formed and can’t migrate further, but can induce extreme pressures which can rupture pipes and vessels.
In the case of ice cores, some molecules can escape just prior to full closure of the bubbles. That is the case for Ne, Ar, O2 and others, but not for CO2:
http://www.bowdoin.edu/~mbattle/papers_posters_and_talks/Closeoff_fractionation_EPSL.pdf
In the case of salt: as far as I know, that are very tight crystals and I don’t expect much migration over time. I only wonder what they have included: salt crystals are formed in solution, thus any “air” included is more probably out of the solution and not from the atmosphere…

FerdiEgb
Reply to  Bartleby
July 17, 2016 7:58 am

highley7,
Let the late Dr. Jaworowski rest in peace together with his ideas about CO2 in ice cores. He was an expert about the fallout of nuclear bomb tests and the Tsjernobyl disaster in ice cores, but I haven’t found anything about any work of him on CO2, except a lot of objections in a letter of 1992, which were thoroughly refuted by the work of Etheridge e.a. on three ice cores of Law Dome in 1996.
As CO2 in ice cores is between 180-300 ppmv and the surrounding atmosphere at measuring time was 350-380 ppmv, how can one measure too low values in the ice core, if any migratrion would give an increase in CO2, not a decrease?
Not only that is impossible, but there are too many other impossibilities in his letter… See my objections at:
http://www.ferdinand-engelbeen.be/klimaat/jaworowski.html

Alan Kendall
Reply to  Bartleby
July 17, 2016 8:57 am

A major problem, already noted here and not addressed in the paper, is that the gas in the inclusions would have been dissolved in the brine and is not a sample of the atmosphere. Oxygen levels in halite-saturated brines are very, very low, even when the brine is in contact with an atmosphere with a high oxygen content (like today). The problem with the Proterozoic determined oxygen levels is that the oxygen contents in the inclusion gases are so HIGH, when they would be expected to be very low. I have contacted the first author about this. If I get a reply, I’ll post here.

Latitude
July 16, 2016 3:39 pm

Problem is going to be dating the halite…

Don K
Reply to  Latitude
July 17, 2016 5:08 am

No more problem than dating any other non-igneous rock. If it’s less than about 550 million years old, you look for index fossils in the underlying and/or overlying beds. If older than that, you hope for bracketing layers of lava or tuff that can be radiometrically dated. But you’re right. That can be much harder than it sounds.

Alan Kendall
Reply to  Latitude
July 17, 2016 9:00 am

Age determination of the salt mentioned in paper and relevant references are given. Dating the salt seems secure.

Mark - Helsinki
July 16, 2016 3:40 pm

Where are the proxies from? Assuming these are dry sea bed proxies? How to remove gases from drying sea bed and not atmosphere?

Reply to  Mark - Helsinki
July 16, 2016 5:42 pm

Good question

Reply to  Mark - Helsinki
July 16, 2016 11:49 pm

“Modern halite for testing the oxygen paleobarometer
were recovered from ponds at the Mosaic
salt mine near Carlsbad, New Mexico (USA), and
Lake Polaris, Southern Cross (Australia). The
material consisted of rafts of cumulate halite growing
at the water-atmosphere interface of the ponds,
and their inclusions were tested for N2
, O2
, and Ar
gas contents. The results fall within acceptable
parameters of modern atmospheric air (Fig. 1).
Messinian Halite
Material from the latest Miocene was obtained
from the Racalmuto mine of Sicily. Based on its
fabric and texture, the halite is of the cornet variety
with bands rich in inclusions and precipitated
at the water-atmosphere interface (Fig. DR2). Its
gas content overlaps significantly with those of
the air standards (capillary tubes) and modern
halite from Carlsbad (Fig. 1). This suggests little
change in atmospheric oxygen over the past 6 m.y
Cretaceous Halite
Material from this period covers a time of
controversial atmospheric oxygen gas contents
(Berner and Landis, 1988; see Fig. DR3).
Chevron halite from the Cretaceous Mengyejing
Formation of Tibet gives average oxygen of
25.8%, which is higher than the modern level
of 20.946% (Fig. 1), and supports the assertion
of elevated pO2
during the mid-Cretaceous. It
is highly unlikely that oxygen could have been
injected into halite inclusions without evidence
of morphochemical disruption, and we must
conclude that Cretaceous atmospheric oxygen
was most likely higher than present-day levels.
The tests performed on the modern, Messinian,
and Cretaceous halites support halite’s robustness
as an atmospheric oxygen archive.
NEOPROTEROZOIC HALITE AND
ATMOSPHERE
Our Neoproterozoic halite samples are from
the Empress 1A and Lancer 1 drill cores from the
Officer Basin, southwestern Australia (Fig. 2),
a broad marine shelf tectonically stable since
Neoproterozoic time (Figs. DR4 and DR5). The
samples at the two localities are from the “B”
interval of the Browne Formation (Fig. DR6) that
is bracketed to 830–800 Ma based on chemostratigraphy
and geochronology (Hill and Walter,
2000; Swanson-Hysell et al., 2015). In summary,
the halite samples were screened for their
preservation using petrography, chemistry, and
stable isotope compositions (Lécuyer and O’Neil,
1994; Spear et al., 2014), and Table 1 summarizes
the fabric and geochemical parameters.
The Neoproterozoic halite inclusion gases
are all oxygen depleted relative to modern atmosphere
(Fig. 1; Fig. DR1). Inclusion oxygen from
sample 1478 (Empress core) is low at 1.64%,
and based on depositional and geochemical features,
the halite formed in the salt basin during
rising water level and in dysoxic bottom water
(Schreiber and El Tabakh, 2000). In contrast,
the other halite samples from the Neoproterozoic
Browne Formation are replete with bands
rich in fluid/gas inclusions (Fig. 3). CFS-MS
analysis of inclusions shows average oxygen
contents ranging from 10.15% to 13.43%
(Table 1). Thus, atmospheric oxygen during the
mid-Neoproterozoic was on average 10.9% or
about half of the modern level of 20.95%.

FerdiEgb
Reply to  Steven Mosher
July 17, 2016 8:03 am

Thanks Steve for the clarification. Seems worth to look deeper in this possible proxy…

gymnosperm
Reply to  Steven Mosher
July 17, 2016 8:06 am

This appears to be a nice new tool, and at 800 mya we will take any data we can get, even if it must be taken with a grain of…yet their results are not surprising. It is generally assumed (e.g. Huey and Ward) that atmospheric O2 rose dramatically about 340 mya when large forests first appeared on land, effectively opening 1/3 of the planetary surface to photosynthesis.
The Cretaceous high point is also not surprising as there were very high rates of sea floor spreading, LIP production, and it was hot, driving gasses from the ocean to the atmosphere. The atmosphere was probably just plain bigger then, with higher surface pressure.

Jan Christoffersen
Reply to  Steven Mosher
July 18, 2016 11:34 am

Steve,
Could they also have measured CO2?

July 16, 2016 3:45 pm

I’m not a geologist (my color-blindness bars me from reading those annoying maps), so I’m going to ask a stupid question: is there a way to provide chronological dating for halite the way that we can for ice fields? Is there a dependable way to date these deposits? Otherwise, how can this evidence be effectively used?

R. Shearer
Reply to  Bryan R. Johnson
July 16, 2016 4:04 pm

One ought to be able to date sedimentary layers above and below the salt deposit.

Johnny Cuyana
Reply to  R. Shearer
July 16, 2016 4:19 pm

bryan r. j: as you recognize, correctly, chronological placement is a critical metric; as always, every case is different … as different as the respective geologic setting. even in general, there are way too many physical variables for me/anyone to comment here meaningfully … especially in view of the fact that i have not read the paper.

Bryan Johnson
Reply to  R. Shearer
July 16, 2016 4:41 pm

Ah, good point. As I said, I’m not a geologist. “Older, lower; younger, higher.” I’ll just stick to fishing, thanks.

Duster
Reply to  R. Shearer
July 16, 2016 11:05 pm

Salt (Halite) has several properties that provide lots of hope and gloom simultaneously. Under enough pressure it behaves like a liquid forming “domes” that are the halide equivalent to plutons (a dollop of magma that has worked it way upward into older rocks before crystallizing. Salt domes are important indicator formations in petroleum geology:
http://geology.com/stories/13/salt-domes/
Salt is an evaporite mineral and is always associated with former water bodies (effectively all salt is sea salt, so if you sell it, don’t tell your customers). The final period in the formation of an evaporite before burial would typically involve periods of flooding and desiccation at the surface. Theoretically that means that developing crystals of salt could trap gases and even water. After burial things get far more complex. Deeply buried salt formations prefer not to stay there, so ancient salt formations that haven’t undergone extreme burial and exposure environments are uncommon at the very least. All in all, I would recommend taking the content of the article with pinch of salt.

Duncan
Reply to  Bryan R. Johnson
July 16, 2016 9:12 pm

Aaahh whatever, plus or minus a few million years, after several billion, does it matter? But I must say they last decade has been the worst ever.

Michael Carter
Reply to  Bryan R. Johnson
July 16, 2016 11:08 pm

Bryan
I am red-green colour blind too and ended up with a MSc in Earth science (sedimentary geology). Geology is largely about processes. We can get around the colour problem. Minerals are better identified though other means as colour varies due to impurities. So if your heart is in it go for it. I enrolled at age 44 🙂

Reply to  Michael Carter
July 17, 2016 4:09 am

There are new glasses that allow color blind people to see colors (effective in most cases and some interesting emotional reactions from people that try them for the first time).
Search it on Google.

Gary Hladik
Reply to  Michael Carter
July 17, 2016 10:39 am

Actually, we’re all horribly colorblind, because even “normal” humans can only see a very narrow portion of the electromagnetic spectrum. Maybe someday we’ll have glasses that extend our vision into the ultraviolet and near infrared. Hey! Then could we “see” the so-called “greenhouse effect” all the time?
Hmm, I guess we’re all partially deaf, too:

E.M.Smith
Editor
Reply to  Michael Carter
July 17, 2016 3:36 pm

Some birds have 4 sizes of cones and see more colors than we do. Others, and some mammals have only two sized cones, so see fewer colors. There is no standard color palette for animal vision…
It might someday be possible to genetically add more cones and more colors via genetic engineering, but it will be a while…
Each length cone couples to that wavelength light, so for color vision, size really does matter…

July 16, 2016 3:46 pm

It’s good to see scientists are still vigorously looking for new repositories of palaeo climate and atmosphere data.

Johnny Cuyana
Reply to  ptolemy2
July 16, 2016 4:14 pm

yes, indeed, such investigation continue; perhaps sometimes more so than we think.
real science = search for truth … at once and forever.

Evan Jones
Editor
Reply to  Johnny Cuyana
July 16, 2016 5:03 pm

People(s) generally overreact and are subject to fads, occasionally valid, usually consisting of varying extremities of exaggeration. The usual AGW = CAGW. I have lived through a number of them (but none as quite as bad as this).
As a lukewarmer and a sea monster I would expect another ~15+ years of relative flat followed by ~30 years of ENSO/PDO-related warming at or about the 1977 – 2007 rate. At which point there will be much caterwauling about “tipping points” that have nothing to do with any of this. Then flat again for another ~30.
By that time we’ll almost certainly have left fossil fuels (at least for electricity generation) largely in the dust. And without a single additional regulation, tax, handout, or policy necessary. (If we would get back to reinforcing success rather than propping up inevitable failures government might just possibly play a positive role in all this. But not till then.)

charles nelson
July 16, 2016 3:57 pm

I’m sure that by using just one teaspoon of salt, from one deposit they’ll be able to pin global temperatures 1.9 million years ago down to two decimal points. They’re very clever people these scientists.

Gregory
Reply to  charles nelson
July 16, 2016 7:32 pm

And it will show that it’s worse than we thought.

Mike McMillan
Reply to  charles nelson
July 16, 2016 9:27 pm

They aren’t talking 1.9 million years ago. They’re going back 800 million.

Gary Pearse
July 16, 2016 4:22 pm

I’m with Wryheat and latitude: Halite is, of course, very soluble. You could get a salt layer between, say, Devonian shales or limestones that, under pressure will flow, piercing overlying deposits forming salt domes and diapirs. These “flow by a process of solution and recrystallization on a minute scale. This means trapped gases can easily be lost and new gases trapped. This mineral is too unreliable because of this behavior. Small pods of salt near the surface may have dissolved when the environment was wet and recrystallized when arid conditions returned. I would need to see the paper to see how they are given assurance that the age of the salt deposit is the same as the enclosing rocks.

Reply to  Gary Pearse
July 16, 2016 11:54 pm

paper is open acces
Overall, the original halite crystal fabric must
be devoid of any depositional and/or post-depositional
tectonic and/or halotectonic folding,
faulting, and fracturing to allow the preservation
of bedding and crystal fabrics and textures
(Spear et al., 2014). Recrystallized or diagenetically
formed halite may be identified by
unusually large, distorted, sporadically distributed
interlocking mosaics of clear crystals with
large and abundant inclusions (Schreiber and
El Tabakh, 2000). Halite cement forms during
early burial, and the entire process is complete
by ~45 m depth (Casas and Lowenstein, 1989),
and afterward halite is no longer susceptible to
dissolution and alteration except under hightemperature,
fluid burial, and tectonic conditions.
Geochemistry may be an additional screening
tool to identify the primary state of inclusions
in halite. Bromine and d34S are two such tools
to ascertain the primary and marine nature of
halite. The sulfur isotope composition is largely
controlled by the sulfur content of the ambient
but geologically variable seawater, whereas Br
content will range from 65 to 75 ppm at the
onset of halite crystallization, depending on the
partition coefficient, and reach ~270 ppm at the
offset (McCaffrey et al., 1986). Also, the major
ion chemistry of the inclusion fluids reflects the
preservation potential of the halite (Spear et al.,
2014). Maturation of halite deposits is generally
complete within 45 m of burial manifested
by the occlusion of all intercrystalline porosity
by clear halite cement (Schléder et al., 2008).

Neil Jordan
July 16, 2016 5:03 pm

Natural sea salt contains potassium chloride along with sodium chloride. If there is any potassium in the halite, then there is natural radioactive potassium-40. Potassium-argon dating might be possible:
http://www.sciencedirect.com/science/article/pii/0016703780901532
“Abstract Polyhalite, K2Ca2Mg (SO4)4-2H2O, is an important mineral in many evaporites. Although its use for K-Ar dating has never been investigated, our results indicate that it is a very useful mineral for dating events ranging from the time of potash mineralization to any younger events which may have affected the evaporite. . .”

The other Phil
July 16, 2016 5:50 pm

We should all read this with a grain of salt (someone had to say it).

commieBob
July 16, 2016 6:23 pm

From the abstract:

The measured pO2 puts oxygenation of Earth’s paleoatmosphere ∼100–200 m.y. ahead of current models and proxy studies. It also puts oxygenation of the Neoproterozoic atmosphere in agreement with time of diversification of eukaryotes and in advance of the emergence of marine animal life.

It sounds to me as if Blamey et al. are attributing the diversification of eukaryotes (800 million years ago) to an increase in oxygen. They use that as evidence that they have correctly dated the increase in oxygen.
As far as I can tell, nobody else thinks the lag between the diversification of the eukaryotes and the rapid increase in atmospheric oxygen is a problem.

Paul Westhaver
July 16, 2016 7:01 pm

Wouldn’t the halite be forming at the ocean -to- atmosphere boundary? In which case the O2 would be some average of 02 dissolve in the atmosphere and ocean?
Am I off base?
http://img.earthshots.org/2011/full/356.jpg

Reply to  Paul Westhaver
July 16, 2016 7:36 pm

Once the saline solution reaches saturation, the crystals will form anywhere a crystal lattice can initialize.

Paul Westhaver
Reply to  ATheoK
July 16, 2016 8:09 pm

OK. So why the assumption regarding atmospheric O2? Is dissolved O2 an indicator of atmospheric O2 regardless of temperature, pressure, and other elements and compounds? Seem like a leap to me.

Reply to  ATheoK
July 17, 2016 6:16 am

No disagreement from me there, Paul.
I doubt O2, CO2 or many gases just squeeze into the crystal lattice; but many crystal lattices can have voids where foreign materials get included.
What remains unproven is that sodium chloride halite crystals can provide pure unchanged atmospheric gases from any specific time.
Especially since all it takes to alter halite crystals is humidity that halite can draw moisture from, dissolve the exterior and then re-crystallize when dryer air moves in.
Even very dry ground samples have a certain proportion of moisture content.
Bringing us back to that bit of science that climate mumbo jumbo likes to avoid. ‘Extraordinary claim(s) require extraordinary evidence.’
Simple correlation studies are insufficient to ‘prove’ halite age analysis. There should be extensive laboratory tests that conduct multiple levels of lab tests on many samples.

Paul Westhaver
Reply to  ATheoK
July 17, 2016 4:09 pm

Ok That is what I was thinking. What is the calibration reference.? The paper refers to proxy…???

Shoshin
July 16, 2016 8:00 pm

Another issue is the clay content of the salt deposit. Clays are well known to adsord/desorb gasses under various pressure regimes. CO2 and methane are common gases that clays can affect. THis has always been one of my biggest concerns about ice core data. And yeah, I’m a rock jock.

tty
Reply to  Shoshin
July 17, 2016 1:44 am

And yes, there are clay minerals from dust in glacier ice. Mostly from the Gobi in Greenland and from Patagonia in the Antarctic. And most dust (=clay minerals) during glacial maximums when CO2 is at a minimum. Hmm…

Dr. Strangelove
July 16, 2016 8:31 pm

“This discovery has applications beyond the origin of life, to pinpointing the genesis of economic metal deposits, and application of this important scientific discovery to the search for life on extraterrestrial bodies.”
How is this relevant to finding metals and aliens? Sodium is a metal but we’re more interested in gold, silver, copper, lithium, iron, aluminum, etc. Get salt rock samples from exoplanets and look for traces of oxygen?

William
July 16, 2016 8:48 pm

Surely there are some trees nearby.
Just count the rings, and all will be revealed.
Why does everybody always try to find something wrong with it?

jorgekafkazar
Reply to  William
July 16, 2016 9:13 pm

Because, historically, there’s usually “something wrong with it.” E.g., models used to verify a hypothesis, rather than test it. If we’re cynical and sarcastic, it’s only to be expected, given the poor state of post-Normal Science. I even read the redoubtable* researcher’s name as “Nigel Blarney” several times.
* This may not mean what you think it does.

William
Reply to  William
July 17, 2016 3:08 am

Whoops!
Forgot the /sarc tag.

rtj1211
July 17, 2016 1:47 am

It’s usually a good idea, if you are going to claim something as a ‘paradigm shift’, to point out to your channels of communication just how that shift will impact on things.
To me, this is just another tool in the armoury of climate geologists, finding another set of samples to measure gas concentrations.
Please explain what is so unique about rock salt as compared to any other rock form and hence which vast new vistas can be opened up to forensic analysis as a result……

Wim Röst
July 17, 2016 2:08 am

The Antarctic Epica Dome ice core brings us only back an 800.000 years. So any extension in time of the research of the ‘enclosed bubbles’ can give us much extra information.
But indeed, the right interpretation will be difficult, given the many circumstances of depositing the salt and given the plasticity of the salt. The following picture gives an image of the possible salt structure from the Realmonte Salt Mine in Sicily:
http://66.media.tumblr.com/d324289021341ed74f0aa666da7e545f/tumblr_n4eip5U86O1rhb9f5o1_r1_1280.jpg

Alan Kendall
July 17, 2016 2:41 am

There have been some comments here expressing scepticism suggesting the halite and its inclusions will have suffered change and therefore the conclusions the authors reached about the Proterozoic atmosphere are suspect. Having read the paper I can be reassuring. A thinsection photograph of the halite within the paper shows growth bands defined by fluid inclusions. If there had been any resetting of the inclusions that would have caused the elimination of the inclusions or, at the very least, their migration within the halite crystal. The preservation of the growth lines indicates no such changes have occurred.
My only criticism of the paper is that the Proterozoic halite was all of the chevron halite type but the recent halites were all cumulate. There would have been no problem sampling modern chevron halites – most salt crusts are composed of them. It also would have been possible to artificially grow halite in the laboratory with different oxygen levels.
The authors will have problems extending their study. There are few, if any, other well preserved halites in the Precambrian for them to sample.

Gamecock
July 17, 2016 3:35 am

‘This discovery has applications beyond the origin of life, . . . to tracking atmospheric changes in carbon dioxide and methane with climate change, . . . .’
They struggle for relevance. Basic research is dead; all research is applied.

tadchem
July 18, 2016 4:41 am

Salt does not crystallize from air. It crystallizes from salt water (brine). Any oxygen trapped in inclusions within the crystal came from that brine solution, and had been subject to the biological processes of the denizens of that brine. These biological processes alter the isotope ratios, so the isotope ratios are NOT a good proxy for the atmosphere.

Resourceguy
July 18, 2016 7:01 am

Okay, let’s look at the huge salt formations in the Gulf of Mexico and offshore Brazil.

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