ROCK DOCTORS THROW ANCIENT STONES

MARBLE BAR CHERT IN THE PILBARA, IN AUSTRALIA'S FAR NORTH-WEST: 3.46 BILLION YEARS OLD? THE RED BANDS CONTAIN THE IRON OXIDE, HAEMATITE, WHICH PROVIDES CLUES THAT ORGANISMS WHICH COULD PHOTOSYNTHESISE WERE ALIVE AND WELL 700 MILLION YEARS EARLIER THAN PREVIOUSLY THOUGHT. PHOTO: Dr. ARTHUR HICKMAN

Canada v. Australia In Oldest Life Arguments
Barossa Boasts Looking Really Silly Now
by PHILIP WHITE

Barossa winemakers claiming their soils and geology are some of the oldest on Earth might like to bone up on news from northern Canada and Australia’s Pilbara, in our far north-west.

Geologists working in the Pilbara have published an article in today’s Nature Geosciences, claiming that simple photosynthesising life forms were farting oxygen into the oceans 700 million years earlier than previous estimates. Masamichi Hoashi, David C. Bevacqua, Tsubasa Otake, Yumiko Watanabe, Arthur H. Hickman, Satoshi Utsunomiya and Hiroshi Ohmoto are the rockdoctors concerned.

“The timing of the origin of photosynthesis on the early Earth is greatly debated”, they write.

“It is generally agreed, on the basis of the presence of biological molecules found in shales from the Hamersley Basin, Australia, that oxygenic photosynthesis had evolved 2.7 billion years ago. However, whether photosynthesis occurred before this time remains controversial. We report primary haematite crystals and associated minerals within the marine sedimentary rocks preserved in a jasper formation of the Pilbara Craton, Australia, which we interpret as evidence for the formation of these rocks in an oxygenated water body 3.46 billion years ago. We suggest that these haematite crystals formed at temperatures greater than 60 °C from locally discharged hydrothermal fluids rich in ferrous iron. The crystals precipitated when the fluids rapidly mixed with overlying oxygenated sea water, at depths greater than 200 m. As our findings imply the existence of noticeable quantities of molecular oxygen, we propose that organisms capable of oxygenic photosynthesis evolved more than 700 million years earlier than previously recognized, resulting in the oxygenation of at least some intermediate and deep ocean regions”.

This key finding is critical in the unfolding natural history of Earth. Microscopic organisms such as cyanobacteria create oxygen as a by-product of photosynthesis. The date of their arrival is an essential key to our understanding of the evolution of life.

“The evidence comes from tiny crystals of the iron-oxide mineral haematite in a 160-metre-long core section that forms part of the Marble Bar Chert”, reported Heather Catchpole on ABC Science.

“Haematite can form in the presence of aerobic or oxygen-loving bacteria in the water, or by photo-electric processes in the upper 10 metres of seawater.”

“Microscopic analysis of the rocks show no sign of wave action or other structures characteristic of shallow-water sediments” Catchpole explains. “The orientation and nature of the grains of haematite also show that it precipitated directly from the seawater, rather than forming later from other processes, such as the movement of groundwater.

“These data strongly suggest that oxygenic photoautotrophs flourished in the photic zone of the 3.46 billion-year-old oceans and supplied molecular oxygen to the deep water.”

This new research presents a problem for those with previous findings: geology Professor Malcolm Walter, from the University of New South Wales, says previous research suggests a much later date for the evolution of photosynthesis.

“Evidence from uranium deposits and iron-rich rocks in the nearby Hammersley region of Western Australia point to the earth's atmosphere and oceans first becoming oxygenated around 2.4 billion years ago” he says. “[This new claim] suggests that photosynthesis must have evolved before 3.5 billion years ago and that despite that, it took one billion years to oxygenate the surface of the earth. That's hard to reconcile with what we know about how this sort of bacteria would have spread”.

But researcher Professor Hiroshi Ohmoto from the NASA Astrobiology Institute and Department of Geosciences at the Pennsylvania State University says other data backs their claim for an early development of photosynthesising life.

“Recently accumulated massive amounts of geochemical and biochemical data can be better explained by a theory postulating the emergence of oxygenic photosynthesis and the development of a fully oxygenated atmosphere in the very early evolutionary stage,” Professor Ohmoto said. “Once cyanobacteria appeared in one area of the ocean, it probably took less than 10 million years to fully oxygenate the atmosphere and oceans.”

Another team, working on the Nuvvuagittuq greenstone on the tundra on Hudson Bay, Canada, say these are Earth’s most ancient rocks, at 4.28 billion years of age. They claim these are 250 million years older than any other rocks known.

DON FRANCIS AND JONATHON O'NEIL OF McGILL UNIVERSITY, MONTREAL, AT WORK ON THE NUVVUAGITTUQ GREENSTONE

Writing last year in Science Journal, this team claims their pet rocks may contain evidence of the earliest life. Co-author Don Francis, geology professor at McGill University in Montreal, cautioned that this had not been established.

“The rocks contain a very special chemical signature - one that can only be found in rocks which are very, very old,” he said. “Nobody has found that signal any place else on the Earth. Originally, we thought the rocks were maybe 3.8 billion years old. Now we have pushed the Earth's crust back by hundreds of millions of years. That's why everyone is so excited.”

BBC science writer, James Morgan writes that before this study, the oldest whole rocks were from a 4.03 billion-year-old body known as the Acasta Gneiss, in Canada's Northwest Territories. (The only things known to be older are mineral grains called zircons from Western Australia, which date back 4.36 billion years.)

Professor Francis and his McGill University colleague, Jonathan O'Neil, sent Nuvvuagittuq greenstone samples to the Carnegie Institution of Washington, where they were dated by measuring isotopes of the rare earth elements neodymium and samarium, which decay over time at a known rate.

The oldest rocks, termed faux amphibolite, were dated within the range from 3.8 to 4.28 billion years old. “4.28 billion is the figure I favour,” says Francis. “It could be that the rock was formed 4.3 billion years ago, but then it was re-worked into another rock form 3.8bn years ago. That's a hard distinction to draw.”

The same unit of rock contains geological structures which might only have been formed if early life forms were present on the planet, Professor Francis suggested.

The material displays a banded iron formation - fine ribbon-like bands of alternating magnetite and quartz. This feature is typical of rock precipitated in deep sea hydrothermal vents - which have been touted as potential habitats for early life on Earth.

“These ribbons could imply that 4.3 billion years ago, Earth had an ocean, with hydrothermal circulation,” said Francis. “Now, some people believe that to make precipitation work, you also need bacteria. If that were true, then this would be the oldest evidence of life. But if I were to say that, people would yell and scream and say that there is no hard evidence.”

“The exciting thing is that we've seen a chemical signature that's never been seen before. That alone makes this an exciting discovery”, he said.

For the information of winemakers who don’t understand the difference between rocks and soil, prone to make blithe back label claims about the oldest soils on Earth, the oldest rocks in the South Australian vignobles are from the neoproterozoic, which concluded about 540 million years ago and stretched back another half a billion years before that.

Unlocking The Rocks

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CONTRIBUTION TO THE 2008 GREENOCK CREEK VINEYARDS AND CELLARS NEWSLETTER

by PHILIP WHITE – September 2008

Time for some rough science. While global warming is such a hot topic cough cough it seemed perfectly appropriate to take a little geology lesson: geology shows we’ve had global warming before. So, like, how bad can things get?

Before you check out Snowball Earth on Wikipedia, let me quote a report of Hoffman, Kaufman, Halverson and Schrag, suggesting one of the things that happened at the bottom of the Neoproterozoic groups which underly Greenock.

“… biological productivity in the surface ocean collapsed for millions of years. This collapse can be explained by a global glaciation (that is, a snowball Earth), which ended abruptly when subaerial volcanic outgassing raised atmospheric carbon dioxide to about 350 times the modern level….resulting in a warming of the snowball Earth to extreme greenhouse conditions. The transfer of atmospheric carbon dioxide to the ocean would result in the rapid precipitation of calcium carbonate in warm surface waters, producing the cap carbonate rocks observed globally.”

I’m sure they make a big difference, but there were no Hummers in those days.

It was also high time the Barossa seriously compared local wines according to their geological sites. But fearing that they may end up with a geology somehow less desirable than others, some vignerons have opposed such an approach for decades. Their excuse? They say they don’t want an appellation imposed like those of France. My response? It’s not a man-made imposition. It’s in the ground beneath you. It was there first.

So a highlight of my thirty years of wine writing finally exploded like a firework, when, in June, I was invited to assist the Barossa winemakers assemble a blind tasting of 52 unfinished 2008 shiraz wines from across the breadth and length of the Valley, from Lyndoch to Kalimna. These were tasted in brackets roughly according to their geological sources, as set out in The Geology of the Barossa Valley, a brochure and map by revered government geologist, W. A. Fairburn. This work, which has the authority of having been gnawed over by the author's scientific peers, is available from Primary Industry and Resources SA. We also had input from the contrary geologist-turned tea-trader turned wine-merchant turned wine-blogger David Farmer, who is writing a book on Barossa geology, and who disagrees with some of Fairburn's mapping.

The tasting was astonishing, while predictable enough. Neighbouring vineyards in each precinct offered flavours and aromas in common, and these characteristics changed from precinct to precinct. This pioneering tasting, conducted with thirty wine writers from around the world, will no doubt be the first of many such exercises, and marks the beginning of a whole new database of gastro-geology.

The base rocks around Seppeltsfield, the Greenock Creek homestead, and Roennfeldt Road are all from that Neoproterozoic, the geological era in which multi-cellular life first appeared. This era stretches from about 550 million years ago to 1.2 billion years. Just for reference, the Universe seems about 13 - 15 billion years old; Earth about 4.5 billion. While these old rocks are generally below the topsoil, they do extrude, and have of course influenced and added to the formation of much of that soil, which very directly influences the flavours of the grape.

But it’s those base rocks that really interest me, particularly when I read back labels and brochures claiming “our vines are grown in some of the oldest soils on Earth”. Most of the Barossa geology formed in the Tertiary and Quaternary, the last 50 million years; its soils are only tens of thousands of years old: most of them are such recent alluviums they’re barely soils at all. “To the geologist, soil is the dandruff of the Earth”, my friend Wolfgang Preiss, Chief Geologist of the Geological Survey in PIRSA, sagely uttered on a recent field trip.

The Greenock Creek vineyards are on four quite distinct formations. The creeklines, both at the homestead and Roennfeldt’s, are very recent alluviums, just tens of thousands of years old. The cabernet, the Creek Block shiraz, and most of the Apricot Block are in such alluviums. These deposits fill the creeklines between the sharply-dipping older strata which protrude in the ridges.

These include the blue-grey dolomitic siltstones - Willunga slate, for example - of the Tapley Hill Formation, deposited as sediments in still deep lakes that once covered the area about 750 million years ago. The Seven Acre and part of the home blocks are in this formation.

Below that lies the Yudnamutana Subgroup. This dark mix of siltstone-derived soil with blotches of bright quartzite and pebbly dolomite is up to 800 million years of age. These layers reappear in Clare and the Adnyamathanha country of the North Flinders. They are pocked with dropstones, which were deposited by floating glacial ice floes. These rocks were one of the fascinations of the great geologist and explorer, Sir Douglas Mawson. Alice’s and part of the Apricot Block are in Yudnamutana.

The Hopeless Hill, on Roennfeldt’s, is on the border of the Yudnamutana and the underlying Burra Group, where we get to really ancient glittery micaceous schists, metasiltstones, calcsilicates and quartzites. These are as old as it gets in the Barossa. The Roennfeldt shiraz, cabernet and the Cornerstone Grenache are in Upper Burra.

In geology, there are many arguments. But having finally got this sorted better than ever before, I’ll never approach Greenock Creek wines in the same way. The distinguishing characters of each vineyard already make much more sense, and the differences between the Greenock Creek/Marananga/Seppeltsfield/Roennfeldt vineyards and the much younger formations in the rest of the Valley become even more meaningful.

So that’s the ancient history. Contemporary history includes the salination, through introduced irrigation water, of the young creekline sediments and clays. And, of course, it includes current weather and climate. People are finally beginning to understand my salination theories. Now, the pace at which the climate is changing must force closer investigation, much quicker than anybody has imagined necessary. If, in a couple of decades, man can change the soil sufficiently to kill a vineyard, like the poor old Creek Block, never irrigated, but dying through salination from upstream irrigators, we can surely bugger up our air.

Or maybe old Mother Earth will just carry on doing what she did before. Now and again, as geology shows, something makes her lose her cool.

PS.

Just to put all this perspective, Don Francis, professor of geology at McGill University in Montreal, has since reported in Science journal that his team has found a sample of Nuvvuagittuq greenstone on Hudson Bay that they believe is 250 million years older than any other rocks known.

"The rocks contain a very special chemical signature - one that can only be found in rocks which are very, very old," he said. "Originally, we thought they were maybe 3.8 billion years old. Now we have pushed the Earth's crust back by hundreds of millions of years. That's why everyone is so excited."

Before this study, the oldest whole rocks were from a 4.03 billion-year-old body known as the Acasta Gneiss, in Canada's Northwest Territories, and the oldest Australia had to offer were 4.36 billion years old mineral grains called zircons from Western Australia.

The greenstone contains fine ribbon-like bands of alternating magnetite and quartz, typical of rock precipitated in deep sea hydrothermal vents - which have been touted as potential habitats for early life on Earth.

"These ribbons could imply that 4.3 billion years ago, Earth had an ocean, with hydrothermal circulation," said Francis. "Now, some people believe that to make precipitation work, you also need bacteria. If that were true, then this would be the oldest evidence of life. But if I were to say that, people would yell and scream and say that there is no hard evidence."

(This additional information was taken from http://news.bbc.co.uk/2/hi/science/nature/7639024.stm )

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