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.