The Earth Story

Saint George Basin Out in the far north of Western Australia and only accessible by air or boat lies this beautiful blue harbour carved by the rising sea at the end of the last ice age out of the ancient rocks. The dark green areas are tidal flats filled with mangrove forests that are submerged by the twice daily high tides, while the rest of the bay is bounded by steep cliffs. At the lower right, the Prince Regent River joins the basin, and the whole area is part of a UNESCO Biosphere Preserve of the same name, now incorporated into a larger national park encompassing the whole Mitchell plateau.

The Bitter Springs Chert Formation

The Bitter Springs chert formation is located at the North East of the Amadeus Basin in Central Australia. This formation is made up of dark limestones and finely laminated layers of black chert (a fine-grained sedimentary rock). This chert is known as chalcedonic (fibrous translucent white/grey quartz). This particular formation is of special interest as despite the fact its 850 million years old it contains very well preserved Proterozoic (2500 to 542 million years ago) fossils. These fossils include 30 species of microfossil (<4mm), including cyanobacteria (bacteria that gain energy through photosynthesis), fungi and dinoflagellates (single celled micro-organism with no skeleton and largely photosynthetic). These are so well preserved that in a thin section under a microscope 3D morphology can be seen. Due to this fact it can be seen that cyanobacteria have always been morphologically similar to how they appear today. The formation also shows stromatolites (as seen in the picture, layered structures made up of sedimentary grains which are trapped by sticky mucous layers secreted by cyanobacteria) and proves they are the product of cyanobacteria.

This formation also contains evidence of early eukaryote (cells containing a nucleus and organelles such as mitochondria and chloroplast) cell fossils. These cells have preserved some structures inside them such as their nuclei (contained the cell’s genetic material when it was alive).

~SA Picture: http://bit.ly/1PuUmg8 by Daderot Paper: http://bit.ly/1EUZYOb by J. William Schopf Further reading: http://bit.ly/1PuUc8C

Banded Iron Formations – an insight into early life on Earth

While the earth formed some 4.5 billion years ago in the Hadean Eon, most of the rocks we see nowadays are much younger than that. Looking at changing rocks through time we can see a number of distinct environments and time periods represented, such as the impressive exposures of white chalk from the Cretaceous Period, but relatively few opportunities to study the very oldest rocks on the planet remain. On Earth, through the combined actions of metamorphism, erosion and remelting of rocks, Hadean rocks are in very short supply. More samples exist from Earth’s next Eon, the Archaean, including fascinating examples like these that imply a very different world. Banded iron formations (BIFs for short) are distinct, layered, and often heavily deformed rocks. Typical BIFs show repeating, consecutive, iron-rich and iron-poor layers; bands of a few millimetres to centimetres of black, silver or grey iron oxides such as haematite (Fe2O3) or magnetite (Fe3O4) alternate with layers of sediment lacking in iron, like shale or chert that are often red in colour, producing a beautiful layered effect. These formations are therefore an excellent indicator of the Earth’s early environmental history.

About 2.4 billion years ago, oxygen first appeared in Earth's atmosphere, the product of organisms called cyanobacteria which first developed the process of photosynthesis around that time. Prior to this, oxygen generally reacted with dissolved iron or organic matter in the oceans, but once these sources became oversaturated O2 started to fill the atmosphere; this is often referred to as the Great Oxygenation Event, the first accumulation of biologically induced oxygen.

Without oxygen in the atmosphere, iron does something we're not familiar with today - it actually dissolves in water and can be held in the oceans like salt. Once oxygen began building up in the atmosphere, suddenly all this iron became insoluble, started precipitating out and sinking to the sea floor. This appears to have been a periodic process; periods of abundant dissolved iron alternated with periods of limited dissolved iron and formation of cherts and shales. Once enough oxygen was present to use up the iron dissolved in the oceans, BIFs could no longer form, so the planet no longer makes them today. Their age usually means that they have been subject to a number of deformation processes, producing beautiful folded effects in specimens. Banded iron formations truly are a unique insight into early planetary history. ZM

Further information:

Genesis of Banded Iron Formations: http://econgeol.geoscienceworld.org/content/89/6/1384.abstract Banded Iron Formations: http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Banded_iron_formation.html

Image credit: http://www.flickr.com/photos/jsjgeology/14872616219/

Figure: Folded jaspilite BIF (Hamersely Group, Neoarchean to Paleoproterozoic, ~2.47-2.55 Ga; Hamersley Range, Western Australia)

Mantle changes allowed oxygen to reach the air.

For the first couple of billion years of our world's history our planet was a pretty bleak and barren place. Life sole handhold on the Earth's rocky and watery skin consisted of extremophile bacteria until one of them managed to use a different chemical pathway to feed: photosynthesis. The culprits were cyanobacteria (aka blue green algae, covered at http://tinyurl.com/lmwmbry) and they eventually poisoned off most of the existing ecosystem, pushing it into increasingly niche habitats, where they remain today.

They did this by giving off free oxygen, which is normally very reactive and therefore binds quickly to other elements. The photo shows one of the consequences, marine banded iron formations from western Australia. As the molecule that made the world (as a recent book would have it) slowly spread the iron erupted in volcanic gases in the atmosphere and dissolved in the oceans bound to it and sank to the sea bottom. Once it was all used up, the molecule we all depend on for respiration started entering the air, where it slowly grew to its current 21%. This was the first of three main pulses of oxygenation known as the Great Oxygenation Event (GOE).

Research published in Nature last year suggests that the Earth made its own contribution to the process: there was an unexplained large decline in mantle melting that created ideal conditions for the event to happen. The team built a database of trace covering 70,000 samples of basalt in order to create a geochemical timeline of Earth's history, and discovered this mysterious drop that was roughly coincident with the GOE. They analysed the trace elements in the basalt and discovered that both the intensity and depth of mantle melting plummeted. They confirmed it using granites, formed from crustal melting, but with the heat energy often rising from the mantle.

Much of the world's iron comes from the weathering of volcanic rocks and erupted gases rich in iron. Melting got shallower and therefore the lavas and gases less iron rich, and combined with the decline in volcanism that followed that in melting, led to less iron dissolved in the air and oceans to soak life's molecule up, allowing oxygen to reach the atmosphere. The reductions in the iron contribution from volcanic gases are particularly important as they would have reacted with any oxygen as soon as it was released into the air. Their lowering made the chemical space for O2 to flourish.

This is the strongest empirical evidence yet for a connection between the depths of the Earth and the GOE, based on a statistical evidence of the preserved traces of deep geochemical activity in the rock record. Their evidence is more precise and detailed than any so far, allowing for better correlations to be reached with a greater degree of confidence. This is also the first hypothesis that answers the question of how did cyanobacteria overcome the chemical oxygen sinks in the seas and air in order to release free oxygen. The simple answer is that those sinks diminished, and by the time they increased again there was enough photosynthesis to absorb them all, and two billion years of built up sink had been reacted away into sea bottom forming the beautiful red rocks in the photo.

So there we have it, while the air we breathe was made useful for our kind of life by photosynthesis, it may be thanks to a change in the depths of the Earth that the oxygen we need established itself in the atmosphere. This led of course to the gradual evolution of oxygen respiring life, leading to where we are today, 2.5 billion years later.  

Loz

Image credit: Simon Poulton.

http://www.princeton.edu/research/news/features/a/?id=7554

Plymouth Rock

Sometimes it’s not just geologists who celebrate a wondrous rock!

Plymouth Rock is the traditional landing site for the pilgrims of the Mayflower. Many visitors are underwhelmed at the stone celebrated as America’s birthstone. It is, after all, just a boulder, and originally it weighed in at about 10 tons (~3 cubic meters in size).

Is this even the real Plymouth Rock? Maybe – only the oral history of an old man in 1741 claimed that it was. However, whether real history or legend, the story “took.” And in 1774, it took 20 teams of oxen to drag the thing from the shore to the town square, or half of it anyway, since it broke into two pieces in the attempt. The rock again broke into two pieces in 1834 while being moved to the front lawn of the town museum. The rock has suffered so much touristic vandalism that small chunks of it can be found in suspicious museums (like the Smithsonian) all over the country.

Geologically speaking (hey, this IS the Earth Story), it’s a glacial erratic: that means, it was carried to this site by a glacier of the distant past (estimated to be ~20,000 years ago in this case) and dumped onto the shoreline when the glacier melted away. Petrologically, it is granodiorite (a medium- to large-grained plutonic rock that is just a bit less rich in quartz than a more normal granite) interpreted to be part of the Dedham Granite.

Dedham granite crops out in several plutons around Boston Harbor, and has been zircon dated to ~607 – 630 million years in age (latest Proterozoic). It is interpreted as originating from the partial melting of even older sedimentary protoliths. As plate tectonics go, at the time of its formation, this granite (including what would someday be Plymouth Rock) was part of the supercontinent Pangea; when Pangea split apart ~250 million years ago, the Dedham granite was also split apart, much of it remaining in Africa. Thus, Plymouth Rock can also be considered a geologic pilgrim contributing to the foundation of America.

Today, about half of the boulder that’s supposed to be the original Plymouth Rock is set within an enclosure at Plymouth Rock State Park, and the other half can still be found on Plymouth Harbor in Plymouth Massachusetts.

Annie R. -- Happy Thanksgiving from TES!

http://www.history.com/news/the-real-story-behind-plymouth-rock http://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=MAZdgr%3B0 http://www.newenglandtravelplanner.com/go/ma/southshore/plymouth/sights/plymouth_rock.html

First manganese, then the world!

The rocks you see here being sampled by Caltech grad student Jena Johnson look rather ordinary; somewhat weathered and covered by dirt, but they sit in a key spot for the development of life as we know it. These rocks, found across large portions of South Africa, are just over 2.4 billion years old. That age means these rocks come from the time just before the rise of oxygen, when the mechanism that would allow for photosynthesis was evolving.

These rocks are kinda interesting too. They contain large amounts of manganese, and that’s not a rock type we see very often today; it’s not easy to concentrate manganese into big thick layers of rock.

But right around the time oxygen started being produced by photosynthesis, it could have been possible. Manganese has multiple “oxidation states”, meaning manganese atoms can gain or lose variable amounts of electrons. Manganese (II) has a +2 charge and can dissolve easily in water. Manganese (III) or (IV) don’t dissolve in water; they precipitate out and form solid oxides like those seen in this unit.

That fact makes this unit really interesting because manganese oxides like these could be formed from the processes giving rise to photosynthesis. Manganese (II) could have been dissolved in the ocean and then converted to manganese (III) or (IV) as life began figuring out the steps in photosynthesis.

Even more interesting…the chemical pathways involved in photosynthesis today actually involve manganese. That could indicate reactions involving manganese were involved in the evolutionary steps along the way, and these manganese-rich layers from the right time period might record that step.

How could you tell geologically if that were the case? Well, this unit could do it. Researchers would need to verify that the manganese oxides formed from the seawater but at a time without free oxygen. Basically that would mean that some organism had evolved the ability to take sunlight and use the energy from it, giving off oxidized manganese as a byproduct, but hadn’t yet figured out the next step of giving off oxygen as a byproduct.

Using cores from drilling efforts led by the Agouron Institute, researchers from Caltech in the group of Professor Woodward Fischer have done just that.

They first examined the cores in extremely high detail to understand the textures in the manganese oxides and verified that they were deposited as sedimentary grains. The manganese is distributed throughout the rocks in thin layers and grains and is associated with carbon bearing the isotopic signatures of biologic material. These results mean that the manganese was deposited in a sedimentary environment; it came directly out of the ocean rather than being added by some other process.

Secondly, the researchers examined other minerals in the sample and found pyrite, a diagnostic mineral for the lack of free oxygen. When oxygen is present, pyrite rusts; we even see this today, the iron is oxidized and the sulfide becomes sulfate. This mineral strongly suggests that the manganese oxides formed from waters without free oxygen.

Finally, the researchers also analyzed sulfur isotopes. One of the best pieces of evidence we have for when oxygen began to rise is a change in the behavior of sulfur isotopes; without going into too many details, you can literally say “yes or no” to oxygen being present using sulfur isotopes. That measurement agrees; there was no free oxygen present when these manganese nodules formed.

This group has found rock units that capture a snapshot in evolution. Some sort of bacterium developed the ability to take manganese from the water, use manganese in a process that collects sunlight, grow itself using some of the energy from that reaction, and discard the newly-oxidized manganese back into the ocean, where it would float to the bottom as a sediment.

The bacterium could live off of that process, but it could only do so as long as it had an ample supply of manganese. If the manganese ran out, it couldn’t continue that process. That is, unless it could find in the water some other, more abundant element to use in the process. Eventually, an organism would figure out that water could do just that; it could hold onto the manganese, take what it needs from the water, and release oxygen as the byproduct.

This rock unit is a snapshot of one of the major evolutionary steps that gave rise to life as we know it, and this research has put together a piece of that remarkable story.

-JBB

Image Credit: Caltech http://www.caltech.edu/content/stepping-stone-oxygen-earth

Original paper (PNAS, Subscription required): http://www.pnas.org/content/early/2013/06/20/1305530110.full.pdf+html

THE BELT SUPERGROUP: Take a Walk on the Proterozoic Beachfront

The Belt Supergroup is a Precambrian sedimentary formation that crops out across a wide expanse of Idaho, Western Montana and SE British Columbia., and, due to the splitting and wandering of tectonic plates, it’s highly probable that parts of it are found in Siberia, China, and even Australia.

Study of the Belt is integral in “uniting” the early super-continent of Rodinia, a Meso-Proterozoic Pangaean-like aggregation of nearly all of the earth’s landmasses. Back in the ‘70s when I collected rocks from the Belt, they were thought to be ~800 – 1.5 billion years. Since then, the entire group has been re-dated to ~1.4 to 1.45 billion years in age. The age of the development of the Rocky Mountains that contain the Belt rocks are ~80 million. Geology progresses…

The sediments are in an excellent state of preservation: for so old a formation, there are exposures that look as if they formed yesterday. Some surfaces show the imprints of rain drops and mud cracks left behind when drying from a gentle rainfall. The flow of water over sands and clays formed ripple marks, just as those seen in the shallow waters of today’s rivers and seas. The only fossils that the Belt rocks are famous for are stromatolites (http://tinyurl.com/jvskq22 ), primitive colonies of cyanobacteria that cemented sedimentary particles into accretionary forms. Some reports of other kinds of early life forms turn out to be pseudofossils, though others may be authentic. Walking on the sands of the Belt is, literally, to walk on the beach of the Meso-Proterozoic. A time machine…

Imagining a Proterozoic world, one with no life on the lands and only bacteria in the seas… where else can this sort of environment be envisioned? The similarities between the Proterozoic on the Earth and the early, water-rich and potentially life-bearing era on Mars shed light on the early histories of both planets.

Conveniently enough, some of the best exposures of this supergroup are found in Glacier National Park. If you have the chance, visit the Belt Supergroup – a trip in time and space.

“Here about the beach I wander'd, nourishing a youth sublime. With the fairy tales of science, and the long result of Time…” Tennyson

Annie R

Photo: Logan Pass in Glacier National Park, Montana Downloaded with thanks from http://commons.wvc.edu/rdawes/virtualfieldsites/LoganPass/VFSLoganPs.html

More information: http://formontana.net/slabs.html http://www.nps.gov/glac/forteachers/geology.htm http://www.sciencedirect.com/science/article/pii/S0024493711003811 http://www.agu.org/books/ft/v334/FT334p0007/FT334p0007.shtml

The rock salt time capsule

The composition of 815 million year old air has emerged from tiny inclusions of trapped atmosphere in crystals of rock salt, held within the crystal lattices as they formed when long gone lagoons evaporated back in the late Precambrian. The data was obtained from a drill core from Australia, the team crushed the halite crystals from it and removed the trapped gases for analysis.

The knowledge helps settle a long standing debate as to whether there was enough oxygen around for complex multicellular life to flourish at that time by showing us that there was (it stood somewhere between 10.4 and 13.4 %, substantially lower than the current 21%).

The new methods developed by the team should also allow us to access information from ancient atmospheres from a wide variety of eras, wherever and whenever the conditions were right for salt to be deposited, which will hopefully lead to a much better understanding of the evolution of our globe's airy envelope through the long vagaries of deep time. This has implications for many areas of research, from the evolution of life through the genesis of ore deposits to assessing recent changes in atmospheric gases and their relationship with climate. It will also contribute to evaluating whether salt formations make good repositories for hazardous waste.

Loz

Image credit, a 7cm piece with a chain of halite crystals sitting pretty on a gypsum matrix: Jurgen Steffens

http://bit.ly/2aKONy0 http://bit.ly/2a8VMCx http://bit.ly/2aOh9J9

Original paper, paywall access: http://bit.ly/2avdRJH

Both of these things can’t be right: Part 2

In my last post, I discussed evidence that oxygen first appeared in the atmosphere almost exactly 2.33 billion years ago (http://bit.ly/1sMwXTK). This tiny, just discovered grain, was used to argue that oxygen must have been present in Earth’s upper atmosphere over 2.7 billion years ago…and both of these studies can’t be right.

This is a tiny sphere of iron, about a tenth the diameter of a human hair. It was one of a handful discovered by dissolving a 2.7 billion year old limestone found in the Pilbara region of western Australia. Some of these tiny bits of iron contain crystals of iron-nickel metal at their core, a signature of them being meteoritic in origin. These are therefore the oldest micrometeorites humans have yet found on this planet.

When a micrometeorite hits Earth’s atmosphere, it heats up rapidly and melts, often producing a shooting star. That grain melts quickly and then cools off within seconds to form a solid sphere, allowing a tiny bit of time for chemistry to occur.

Iron metal, when exposed to oxygen, will react rapidly and rust, forming minerals like magnetite and hematite. These reactions can take years at Earth’s surface temperature, but in the atmosphere when the sample is heated to thousands of degrees they can complete in seconds. This reaction is happening all the time today with lots of oxygen in the atmosphere, but there’s no reason why this reaction should happen at all if there was no oxygen in the atmosphere.

These grains, therefore, suggest that there must have been oxygen, in fact a lot of oxygen, in the atmosphere 2.7 billion years ago. There is good evidence that life figured out photosynthesis before this time, so it makes sense that oxygen could be present that early. The only problem is…this makes no sense with the data presented in the last post.

In the last post, I outlined that sulfur isotope changes require a lack of oxygen in the atmosphere until 2.33 billion years ago, 400 million years after these grains formed. How can these two data sets be put together?

The scientists who discovered these micrometeorites suggested one hypothesis and it has been outlined in a number of press reports. Their idea is that the Earth had oxygen in its upper atmosphere and a methane-rich haze in the lower atmosphere. The oxygen in the upper atmosphere could react with these meteorites to rust them, the lower atmosphere could still have very little oxygen, and a temperature boundary created by the haze layer could keep the two parts of the atmosphere from mixing much.

That hypothesis was presented in their paper, but there’s one thing that hasn’t been published yet in the press reports; this mechanism actually can’t work with the sulfur isotope signature!

The sulfur isotope changes I talked about in the last post don’t happen today because oxygen in the atmosphere absorbs light at the same wavelengths required to ionize sulfur. If there is oxygen in the upper atmosphere, above the sulfur, it will actually block the light from getting to the lower atmosphere.

It might well be possible to have a layered atmosphere, with oxygen in the upper atmosphere and methane in the lower atmosphere, as these scientists suggest. However, this mechanism would still shut off the sulfur isotope signal – if the oxygen is higher up in the atmosphere than the sulfur, it will block the light that is thought to cause the sulfur isotope signal!

This is complicated geology. We’re interpreting isotopes in one case and small grains in another case, both of them over 2 billion years old. Both of them tell interesting stories about the early Earth’s atmosphere. The problem is…the stories don’t add together. Both stories cannot be true at the same time - the mechanism for sulfur changes that I talked about in the last post requires there to be no oxygen in the way, while these meteorites were used to argue for oxygen in the way.

There’s something fundamentally missing from our interpretation of this puzzle. One proposal by researchers evaluating this new work is that it’s actually all the sun; the sun could be ionizing both sulfate and water in the upper atmosphere, creating free oxygen that could bond with these meteorites as they enter, but that may not be enough oxygen. This is now an interesting puzzle for future geologists and atmospheric scientists to understand.

-JBB

Image credit: Tomkins et al. http://rdcu.be/ioti

Reference: http://bit.ly/1Tsy6Ih http://bit.ly/27e8FBt

Missing half billion

The first evidence of widespread oxygen in the atmosphere occurs in rocks that are about 2.5 billion years old. That time marks one of the major boundaries on the geologic timeline, the boundary between the Achaean and the Proterozoic. However, that time does not match up with the evolution of oxygen producing bacteria.

Geologic evidence indicates that organisms producing oxygen as a byproduct existed at least as early as 2.8 billion years ago, a gap of several hundred million years. That difference creates a geologic question; how was life generating oxygen if it didn’t build up in the atmosphere?

A team led by Dr. Dawn Sumner from UC Davis investigated a site in Antarctica called Lake Fryxell, in the Dry Valleys of Antarctica. This lake is permanently covered by about 5 meters of ice on average, thin enough for sunlight to get through but thick enough that the waters cannot exchange oxygen with the atmosphere.

The team drilled small cores through that layer of ice and widened it using copper heaters to allow divers into the lake. Those divers went deep enough to observe the environment at the bottom, where the environment goes anoxic (no free oxygen in the water).

In this environment, the scientists found surprising patches of green; the classic color of photosynthetic organisms. They investigated these patches and found that they were small batches of photosynthetic bacteria. During the long Antarctic summer, a small bit of light gets to these depths and the organisms use that light for energy, giving off oxygen.

That tiny bit of oxygen enters the surrounding environment, but it isn’t enough to overwhelm the surrounding anoxic environment. In other words, these pods create a tiny oasis of oxygen around them. A similar environment could explain how oxygen first arrived in the oceans. Tiny bits of oxygen could have formed oases in the ocean over hundreds of millions of years, giving time for other organisms to adapt to the presence of free oxygen in the ocean before the Great Oxygenation Event.

-JBB

Image credit: Tyler Mackey http://bit.ly/1KuHBAl

Original paper: http://bit.ly/1ZRUYai

Mediocre Middle Earth? The boring billion ….

The boring billion, that’s the unattractive name given to Earth’s quiet middle age. For all those folk out there who feel stories of Middle Earth are over-rated, too long, and really rather dull, you may understand (but maybe not appreciate) stories of a long quiescent period that sits in the middle of the geological time scale. There is something of a mystery surrounding the period of geochemical and evolutionary stagnation that seems to have afflicted our planet between 1.8 and 0.8 billion years ago. Life on Earth was established: dominantly as simple prokaryotic single-celled organisms such as bacteria, but the first eukaryotes, with their internal membrane structures and DNA bundles, had by then also emerged. The “great oxidation event” was old news, but oxygen levels in the atmosphere and oceans stuck low compared to today’s values, and remained there for a billion years or so. Prokaryotic bacteria remained dominant, evolution stuttered. Why did nothing more happen for so long?

The answers seem to lie in the biogeochemistry of the whole Earth system. Interactions between life, oceans, and the rock cycle set in place a pattern that was difficult to break. This medieval, middle age, Earth was characterised by deep oxygen-poor (anoxic) oceans. Harvard scientist, Knoll, argues that only the very shallowest surface waters bore oxygen, home of oxygen-metabolising photosynthesisers. Directly below that, sulphur-reducing photosynthesisers, feeding off sulfur washed in from the continents, created a layer toxic to the oxygen-based organisms. As they died and decomposed they sucked any further oxygen out of the system, to create the oxygen-free conditions of the deep ocean. The key to breaking this stasis could have been the introduction of metals, again weathering off the continents or introduced in ocean-floor hydrothermal systems. Sulfur-loving (chalcophile) elements like zinc could have soaked up the sulphur from the oceans to tip the balance in favour of the oxygenating organisms, allowing the development of oxygen in the oceans and then the atmosphere, and releasing the stranglehold on evolution.

More recently, Reinhard, Lyons and co-workers from UC Riverside have been studying the levels of metals like chromium and molybdenum in ocean sediments, laid down in this period. Their results may also indicate that the bioavailability of these metals played a part in releasing the break on the development of the atmosphere and life.

The causes and consequences of those "boring" billion years remain open to debate, but the key seems to lie in understanding the feedbacks between the chemistry of life and the chemistry of the planet. These studies remind us of the intimate association between the two.

~SATR

Photo: Researchers Chris Reinhard (right) and Noah Planavsky dig into ancient ocean-floor shale in north China (Credit: Chu Research Group, Institute of Geology and Geophysics, Chinese Academy of Sciences).

Links: http://ucrtoday.ucr.edu/12843 http://discovermagazine.com/2011/evolution/23-what-happened-earth-boring-billion-years

Horizontal Falls

Known to local western Australians as The Horries, an interesting illusion makes them resemble a pair of waterfalls falling across the surface of Talbot Bay. In fact, the narrow gaps between the rock connecting the mouth of a creek to the sea turn into bores for the rising and falling tides, creating a gushing wave up to 5 metres high and current that leaves the waterfalls as its wake. Of course unlike most waterfalls, this one reverses direction four times a day. Tidal range in the Kimberleys is an impressive 10 metres making for an impressive phenomenon.

The rocks here are part of the McLarty range, an 1.8 billion year old marine succession, including sandstone, quartzite, siltstone, shale and dolomite (magnesium rich limestone) with abundant stromatolite fossils. The first gap is some 25 metres wide, and the second 12.5. it can be visited by boat or on a seaplane tour from one of the nearby towns.

Loz

Image credit: 1: Stephan Ridgeway 2: Richard Costin http://bit.ly/1T1WA9L http://ab.co/1QszueD http://kimberleycoast.com.au/126-2/

Dramatic folding

Sedimentary layers can lead to beautiful sights. In these pictures they spectacularly fold along the sea and display wonderful colors. These formations can be found on Greenland’s east coast in the Kejser Franz Joseph Fjord and in the King Oscar Fjord.

These particular outcrops belong to Greenland’s Eleonore Bay Supergroup. They mainly consist of sandstones and siltstones, as well as calcareous and dolomitic sediments of late Proterozoic age (700 million years old). They are exposed within the Caledonian fold belt, and are generally moderately metamorphosed. The layers were once deposited in a shallow marine basin and folded later on during a mountain building event (orogeny).

Currently only one fifth of Greenland consists of exposed bedrock, the rest of the world’s biggest island is permanently covered by ice and is yet to be explored.

Xandi

Image Credits: http://bit.ly/1Rj2DJt http://bit.ly/1Oq6Qos http://bit.ly/1miKUFp

Sources: http://bit.ly/1Qn6wNn

ANCIENT ORES GIVE CLUES TO EARLY LIFE

Scientists probing a Canadian sulphide ore have confirmed that oxygen levels were very low on Earth 2.7 billion years ago. Microbes were feeding on sulphate in the ocean and had an influence on seawater chemistry during that geological period. The research, led by PhD student John Jamieson of the University of Ottawa and Prof. Boswell Wing of McGill, shows that ancient metal ore deposits can provide clues to the chemistry of Earth’s ancient oceans and therefore the early evolution of life.

Sulphate is created through chemical reactions between atmospheric oxygen and exposed pyrite, an iron sulphide material also known as ‘fool’s gold’. It is the third most abundant dissolved ion in today’s oceans after chloride and sodium; sulphate ions are responsible for about 7.7% of the salinity of seawater.

The research team measured the ‘weight’ of sulphur in samples of sulphide ore from the Kidd Creek copper-zinc mine in Timmins, Ontario, using a mass spectrometer. The abundance of the different isotopes of sulphur was measured to determine the ‘weight’; this indicates how much seawater sulphate was assimilated into the sulphide ore that formed at the bottom on the ocean and is now on the Earth’s surface.

Less sulphate was incorporated into the 2.7 billion year old sulphide ore than into similar ore found at the bottom of present-day oceans. Using this data, the researchers modelled the amount of sulphate present in the seawater of 2.7 billion years ago. Sulphate levels were about 350 times lower than today’s levels. Even though the ancient sulphate levels were very low, the presence of the sulphate ions would have supported an active global population of microbes that use sulphate to process energy from organic carbon.

Sulphide ore deposits are widespread on Earth, though Canada contains the majority of them. The image shows one of the sulphide ore samples analysed for the study. The bright area in the lower left is a "sulphide nodule” which has preserved isotopic evidence of the presence of microbes that fed on sulphate in Earth’s ancient ocean.

-TEL

https://www.mcgill.ca/newsroom/channels/news/mining-ancient-ores-clues-early-life-219461 http://earth-pages.co.uk/2004/09/01/sulphides-in-the-ocean/ http://www.ehow.com/list_6836743_abundant-ions-sea-water_.html http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1647.html Image credit: Prof. Mark D. Hannington

Plymouth Rock Sometimes it’s not just geologists who celebrate a wondrous rock! Plymouth Rock is the traditional landing site for the pilgrims of the Mayflower. Many visitors are underwhelmed at the stone celebrated as America’s birthstone. It is, after all, just a boulder, and originally it weighed in at about 10 tons (~3 cubic meters in size).  Is this even the real Plymouth Rock? Maybe – only the oral history of an old man in 1741 claimed that it was. However, whether real history or legend, the story “took.” And in 1774, it took 20 teams of oxen to drag the thing from the shore to the town square, or half of it anyway, since it broke into two pieces in the attempt. The rock again broke into two pieces in 1834 while being moved to the front lawn of the town museum. The rock has suffered so much touristic vandalism that small chunks of it can be found in suspicious museums (like the Smithsonian) all over the country.  Geologically speaking (hey, this IS the Earth Story), it’s a glacial erratic: that means, it was carried to this site by a glacier of the distant past (estimated to be ~20,000 years ago in this case) and dumped onto the shoreline when the glacier melted away. Petrologically, it is granodiorite (a medium- to large-grained plutonic rock that is just a bit less rich in quartz than a more normal granite) interpreted to be part of the Dedham Granite.  Dedham granite crops out in several plutons around Boston Harbor, and has been zircon dated to ~607 – 630 million years in age (latest Proterozoic). It is interpreted as originating from the partial melting of even older sedimentary protoliths. As plate tectonics go, at the time of its formation, this granite (including what would someday be Plymouth Rock) was part of the supercontinent Pangea; when Pangea split apart ~250 million years ago, the Dedham granite was also split apart, much of it remaining in Africa. Thus, Plymouth Rock can also be considered a geologic pilgrim contributing to the foundation of America.  Today, about half of the boulder that’s supposed to be the original Plymouth Rock is set within an enclosure at Plymouth Rock State Park, and the other half can still be found on Plymouth Harbor in Plymouth Massachusetts.  Annie R. -- Happy Thanksgiving from TES! http://www.history.com/news/the-real-story-behind-plymouth-rock http://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=MAZdgr%3B0 http://www.newenglandtravelplanner.com/go/ma/southshore/plymouth/sights/plymouth_rock.html

The final chapter of the Pre-Cambrian is known as the Proterozoic, and this stretches from the end of the Archean at 2.5Ga to the beginning of the Cambrian 542ma ago. There were several “Big Events” during this time;

The atmosphere of the Earth became “oxygenated” 2.0-1.8Ga it is believed that this was due to the chemical “sinks” of banded Iron and Sulphur being filled, and an increase in Carbon burial. Evidence for a build-up of oxygen in the Earth’s atmosphere comes from “Red Beds”, geological formations that contain abundant amounts of hematite. (http://jgs.geoscienceworld.org/content/141/2/235.abstract) During the Proterozoic, the supercontinent Rodinia formed (formed approximately 1.1Ga and broke up by 750ma)( http://www.ccsf.edu/Departments/History_of_Time_and_Life/PDFs/Rodinia36x36.pdf) Another major event to have happened during the Proterozoic is the theorised “Snowball Earth”, a time when the Earth was in a period of almost total glaciation. Evidence from this comes from global “dropstones” (http://www.swisseduc.ch/glaciers/earth_icy_planet/glaciers15-en.html). There is great controversy surrounding the “snowball Earth” theory, and some doubt that the tropics were also covered in ice sheets. An opposing theory “slushball Earth” has also been put forward, whereby the higher latitudes were covered in Ice sheets and the lower lattitudes a slushy sea and seasonal snow and ice. (http://www.giss.nasa.gov/research/briefs/sohl_01/ and http://www.ias.ac.in/resonance/Dec2003/Dec2003p8-17.htm, ) The first complex single celled organisms and multi cellular life also emerged during the Proterozoic, and famous fossils from this period are known from the Edicaran Hills of South Australia (dated at 630-542ma). Examples of biota from this period include early echinoderms, primitive jelly fish and early relatives of arthropods. (http://www.ucmp.berkeley.edu/vendian/ediacara.html) Links for the Proterozoic; http://www.ucmp.berkeley.edu/precambrian/proterostrat.html http://paleobiology.si.edu/geotime/main/htmlVersion/proterozoic1.html http://www.ucmp.berkeley.edu/precambrian/proterolife.html http://www.ucmp.berkeley.edu/precambrian/proterozoic.php http://www.geol.umd.edu/~tholtz/G102/102prot3.htm -LL Image- Theorised Position of the Supercontinent Rodinia. Image Credit http://www.eoearth.org/article/Ancient_Earth:_The_First_Three_Billion_Years.