Time-Traveling in the Australian Outback in Search of Early Earth

Facebooktwittergoogle_plusredditpinterestlinkedinmail

This story was written by Nicholas Siegler, Chief Technologist for NASA’s Exoplanet Exploration Program at the Jet Propulsion Laboratory with the help of doctoral student Markus Gogouvitis, at the University of New South Wales, Australia and Georg-August-University in Gottingen, Germany.

 

These living stromatolites at Shark Bay, Australia are descendants of similar microbial/sedimentary forms once common around the world.  They are among the oldest known repositories of life.  Most stromatolites died off long ago, but remain at Shark Bay because of the high salinity of the water. (Tourism, Western Australia)

 

This past July I joined a group of geologists, geochemists, microbiologists, and fellow astronomers on a tour of some of the best-preserved evidence for early life.

Entitled the Astrobiology Grand Tour, it was a trip led by Dr. Martin Van Kranendonk, a structural geologist from the University of New South Wales, who had spent more than 25 years surveying Australia’s Pilbara region. Along with his graduate students he had organized a ten-day excursion deep into the outback of Western Australia to visit some of astrobiology’s most renowned sites.

The trip would entail long, hot days of hiking through unmaintained trails on loose surface rocks covered by barb-like bushes called spinifex.  As I was to find out, nature was not going to give up its secrets easily.  And there were no special privileges allocated to astrophysicists from New Jersey.

 

The route of our journey back in time.  (Google Earth/Markus Gogouvitis /Martin Van Kranendonk)

The state of Western Australia, almost four times the size of the American state of Texas but with less than a tenth of the population (2.6 million), is the site of many of astrobiology’s most heralded sites. For more than three billion years, it has been one of the most stable geologic regions in the world.

It has been ideal for geological preservation due to its arid conditions, lack of tectonic movement, and remoteness. The rock records have in many places survived and are now able to tell their stories (to those who know how to listen).

 

The classic red rocks of the Pilbara in Western Australia, with the needle sharp spinifex bushes in the foreground. (Nick Siegler, NASA/JPL-Caltech)

Our trip began with what felt like a pilgrimage. We left Western Australia’s largest city Perth and headed north for Shark bsy. It felt a bit like a pilgrimage because the next morning we visited one of modern astrobiology’s highlights – the living stromatolites of Shark Bay.

Stromatolites literally mean “layered rocks”. It’s not the rocks that are alive but rather the community of microbial mats living on top. They are some of the Earth’s earliest ecosystems.

We gazed over these living microbial communities aloft on their rock perches and marveled at their exceptional longevity — the species has persisted for over three billion years. Their ancestors had survived global mass extinctions, planet-covering ice glaciers, volcanic activity, and all sorts of predators. Once these life forms took hold they were not going to let go.

 

The stromatolites forming today in the shallow waters of Shark Bay, Australia are built by colonies of microbes that capture ocean sediments. (University of Wisconsin-Madison)

The photosynthetic bacteria that built ancient stromatolites played a central role of our trip for three reasons:

  • Their geological footprints allowed scientists to date the evolution of early life and at times gain insight into the environments in which they grew.
  • They eventually harbored the first oxygen-producing bacteria and played a central role in creating our oxygen-rich atmosphere.
  • By locating ever-increasingly older microbial fossils we observed a lower limit to the age of the first life forms.. Given photosynthesis is not a simple process, the first life forms must have been simpler. Speculating, perhaps a few hundred million years earlier so that the first life form on Earth may have originated at four billion years ago.

When viewed under a microscope, you can see the mats are made of millions of single cell bacteria and archaea, among the simplest life forms we know. Within these relatively thin regions are multiple layers of specialized microbial communities that live interdependently.

Bacteria in the top layer evolved to harvest sunlight to live and grow via photosynthesis. Their waste products include oxygen as well as important nutrients for many different bacterial species within underlying layers. And this underlying layer’s waste product would do the same for the layer beneath it, perfectly recycling each other’s waste. The oldest forms of life that we know of had learned to co-exist together in a chemically interdependent environment.

 

Broken piece of a living stromatolite, which was was remarkably spongy and smelled slightly salty, indicative of the hypersaline bay that has contributed to their survival by making bacteria and other organisms undesirable. What was actually most remarkable of the visit to Hamelin pool was how quiet it was. There were no seagulls and other birds because of the hypersaline environment. They had gone elsewhere for their meals. (Nick Siegler, NASA/JPL-Caltech)

 

We saw ripped up portions of the mats that washed upon the shore at Hamelin pool in Shark Bay. A whole ecosystem held in one’s hand. Thousands of millions of years ago ancient relatives of these microbes thrived in shallow waters all around our planet, and left behind fossilized remains. But due to the evolution of grazing organisms these microbial structures are nowadays constrained to very specific environments. In the case of Shark Bay, the very high salt contents of this inlet have warded off most predators providing the microbes with a safe haven to live.

Ironically, the rocks, which help identify these ancient life forms, at the time were just a nuisance for the living microbes.

Small fine grains of sedimentary rock carried along in the daily tides would occasionally get stuck in the sticky mucus the microbes would secrete. In addition, the photosynthetic bacteria found at Shark Bay may have been inadvertently making their own rock by depleting the carbon dioxide in the surrounding water as part of photosynthesis and precipitating carbonate, adding to the grains of sediment trapped within the sticky top layer.

Over time, the grains from both the sedimentary and precipitated rocks would  cover the surface and block the sunlight for which these organisms had evolved to depend on. As an evolutionary tour de force, the photosynthetic microbes learned to migrate upward, leaving the newly formed rock layers behind.

These secondary rock fossils today showcase visually observable crinkly, frequently conical shapes, in stark contrast to abiotic sedimentary rocks. These ancient life forms left behind geological footprints reminding us they were here first.

Nick Siegler of JPL on his Australian Magical Origins Tour.  (Markus Gogouvitis)

Now to the most important contribution of stromatolites – terraforming the Earth.

Living in shallow water, the top most layer of the Shark Bay microbial mats are known to host cyanobacteria, photosynthetic bacteria that produce oxygen as a byproduct. Scientists don’t know what the first bacteria produced as they harnessed the energy of the Sun. But they do know that they eventually started producing oxygen.

In the evolution of life that eventually led to all plants and animals, this was one of the great events. More than 2.5 billion years ago, ancient bacteria began diligently producing oxygen in the oceans. Earth’s atmosphere began to irreversibly shift from its original, oxygen-free existence, to an oxic one, initiating the formation of our ozone layer and paving the way for the evolution of more complex life. Our planet has been terraformed by micro-organisms!

It was in the Karijini National Park where we went back in time (2.4 billion years) and observed an extraordinary piece of evidence for the early production of oxygen in Earth’s oceans, a time before oxygen made a strong presence in our atmosphere.

 

Banded iron formation at Karajini National Park.  (Nick Siegler, NASA-JPL/Caltech)

 

We saw a massive gorge with steep vertical walls carved out by flowing water. As oxygen production by early bacteria increased below the water surface it would react with dissolved iron ions (early oceans were iron-rich) causing iron oxides to precipitate and settle to the bottom.

For reasons not entirely understood — perhaps related to seasonal or temperature effects– the amount of new oxygen temporarily decreased and iron ion remained soluble in the oceans and other types of sediments accumulated, carbonates, slate, and shale. And then, just as before, the oxygen reappeared creating a new layer of precipitated iron.

The result was a banded sedimentary rock, a litmus test to a changing world, where oxygen would be the reactive ingredient leading to larger and more complex life forms. As the oxygen production no longer cycled, the oxygen went on to saturate the ocean and then accumulated in the Earth’s atmosphere eventually to the levels we have today.

 

Banded iron formation at Karajini. (Nick Siegler, NASA-JPL/Caltech)

After a day of looking down at rocks and spinifex it was both a relief and a joy to look up at the glorious Western Australian night sky. Far away from the light pollution of modern cities, each night would greet us with an awe-inspiring starlit sky. It never got old to remember we are part of a vast network of stars suspended in an infinite space.

The nights would start with the appearance of Venus well before sundown followed shortly by the innermost planet Mercury and then Jupiter and Saturn. It didn’t take long after sunset to see the renowned Southern Cross. Mars joined the evening as well, perfectly appearing on the arc called the ecliptic.

But nothing stirred the group more than the emergence of the swath of stars of the Milky Way, the disk of our home galaxy where its spiral arms all lie. The nights would be so clear that one could actually see the dark clouds of gas and dust that block large portions of the galaxy’s stars from shining through. We partook in the well-known tradition connecting individual points of light to form exotic creatures like scorpions and centaurs. But we also we followed the inverted approach of the Aborigines and connected the dark patches. Only then did we see the emu of the Milky Way. I would never have thought of connecting the darkness.

 

Australian night sky, with campfire below.  (Maëva Millan/NASA-GSFC/Georgetown University)

The night sky appeared even more special knowing that each of its stellar members likely host planetary systems like our own. How many of them host life? Maybe even civilizations? The numbers are in their favor.

At the half-way point of our trip we hiked to an ancient granite region in the red rocks of the Pilbara which contain the world’s largest concentration of Pleistocene rock art also known as petroglyphs. These etchings are believed to be 6,000 to 20, 000 years old.

The artists used no pigments, but rather rocks to pound/chisel shapes into the desert varnish, a thin dark film (possibly of microbial origin) that typically covers exposed rock surfaces in hyper arid regions. We came across many stylized male and female figures with highlighted genitalia as well as animals such as emus and kangaroos. Little is known about the people who created these art works. They left no clues to their origin or fate.

 

Rock art by aboriginal people done 6,000 to 20,000 years ago. The shapes were etched into an existing varnish on the rock. (Nick Siegler, NASA-JPL/Caltech)

Pilbara is also where the oldest mineral on Earth –a zircon dated at 4.4 billion years old — was discovered four years ago in the Jack Hills region.  Because of the geological history of the region, it is a frequent (if hardscrabble) site where many geologists and geochemists specializing in ancient Earth do their work.

In the last several days of the tour we encountered ever-increasing older evidence of stromatolites extending out to circa 3.5 billion years, about 75% of the history of the Earth. I expected the quality of the stromatolites to degrade as we went back in time and it looked like I was right until I saw a remarkably large rock in a locality called the Strelley Pool Formation. The rock measuring approximately 1.5 meters in all three directions gave a rare view of ancient stromatolites from all sides and an unequivocal interpretation of past life.

Large and ancient fossil stromatolite at the Strelley Pool Formation, with Siegler and Gogouvitis.  (Nick Siegler, NASA-JPL/Caltech)

The shapes of the embedded rocks formed by the microbial mats from the top view clearly show the elliptical areas where the bacteria inched upwards to acquire sunlight. Regions between the conical stromatolites were filled in by carbonate sediments in ancient shallow waters. These were later chemically altered to silica-rich rocks through alteration and etching of minerals by fluids. Silicified rocks are very weather-resistant, making them a great medium to preserve fossils for billions of years.

The side views of the stromatolite-laden rock revealed the expected conical layered shapes we saw in younger rocks (and in the living stromatolites of Shark Bay). Everything we had learned about stromatolite structures was clearly visible in this circa 3.43 billion year old example. It is astounding to realize that complex phototrophic (light-eating) organisms, even if not yet oxygen producing, were around during the deposition of the Strelley Pool Formation.

 

Detail of Strelley Pool stromatolite fossil.  (Nick Siegler, NASA-JPL/Caltech)

It is not unreasonable to speculate that the earliest life forms are even older by perhaps a few more hundred million years or so. There is evidence for even more ancient stromatolites in Greenland (3.7 billion years old) and isotope carbon evidence, with considerable controversy, in Nuvvuagittuq greenstone belt in northern Quebec, Canada (4.28 billion years old). Hence, life on Earth may have emerged within 500 million years from its formation. That is astonishingly rapid.

Was Earth an exception or the rule? What does that say for possible life on exoplanets?

Our tour came to an end on July 11. We had traveled over 1,600 miles through Australia’s outback, from Western Australia’s biggest city Perth, all the way up to Port Hedland at the north coast. We were privileged to see the country in ways that very few people get a chance to, and to be steeped in the multidisciplinary sciences of astrobiology while seeing some of its iconic ground.

I had seen some of the earliest evidence for life and the pivotal effect it had on our environment. For those 10 days I learned what it was like to be a time traveler.

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Piecing Together The Narrative of Evolution

Facebooktwittergoogle_plusredditpinterestlinkedinmail
A reconstruction of the frond-like sea creature Stromatoveris psygmoglena, which lived during the Cambrian explosion of life forms on Earth.  Newfound fossils of Stromatoveris were compared with Ediacaran fossils, and researchers concluded they were all very early animals and that this animal group survived the mass extinction event that occurred between the Ediacaran and Cambrian periods. (Jennifer Hoyal Cuthill.)

An essential characteristic of life is that it evolves. Whether on Earth or potentially Mars, Europa or distant exoplanets, we can assume that whatever life might be present has the capacity and the need to change.

Evolution is intimately tied to the origin-of-life question, which this column often explores.  Having more answers regarding how life might have started on Earth can no doubt help the search for life elsewhere, just as finding life elsewhere could help understand how it started here.

The connection between evolution and exoplanets has an added and essential dimension when it comes to hunting for signatures of distant extraterrestrial life.

Searching for a planet with lots of oxygen and other atmospheric compound in disequilibrium (as on Earth) is certainly a way forward. But it is sobering to realize that those biosignatures would not have been detectable on Earth for most of the time that life has been present.  That’s because large concentrations of oxygen are a relative newcomer to our planet,  product of biological evolution.

With all this in mind, it seems both interesting and useful to look at the work of a researcher studying the fossil record to better understand a particular transition on Earth — the one from simpler organisms to multicellular creatures that can be considered animals.

The surprising, large transitional life of the Ediacaran period, which just preceded the Cambrian explosion of complex life. This grouping is termed the Ediacara assemblage, and existed late in the period.  (John Sibbick)

The researcher is Jennifer Hoyal Cuthill of the University of Cambridge, who I first met at the Earth-Life Science Institute in Tokyo, a unique place where scientists research the origin of Earth and of life on Earth.

She had been included in a group of twelve two-year fellows recruited from around the world who specialized in fields ranging from the microbiology of extreme environments to the current and past dynamics of the deep Earth and the digital world of chemo informatics.  And then there was Hoyal Cuthill, whose field is paleobiology, with a heavy emphasis on evolution.

Now Hoyal Cuthill has published a paper in the journal Paleontology that describes findings in the fossil record that shed light on that transition from less complex organisms like bacteria, algae and fungi to  to animals.

Her specialty is the Ediacaran period some 635 to 541 million years ago.  This transitional period came after a snowball Earth event and was followed by the Cambrian explosion, when ocean life of all sorts grew and changed at an unprecedented rate.  But as she and others have found, the Ediacaran also had large and unique lifeforms, and she is working to make sense of them.

She described her work and findings more specifically as follows:

“When did animals originate? What were the bizarre, early fossils known as the Ediacaran biota?

“We show that both questions are answered by a frond-like sea creature called Stromatoveris psygmoglena known from exceptionally preserved, Cambrian fossils from Chengjiang County, China.

“Originally described from only eight specimens, we examined over 200 new fossils since discovered by researchers from Northwest University (in Xian.) Stromatoveris was compared to earlier Ediacaran fossils in a computer analysis of anatomy and evolutionary relationships.

“This showed that Stromatoveris and seven key members of the Ediacaran biota share detailed anatomical similarities, including multiple, radiating, branched fronds that unite them as a phylum of early animals, originating by the Ediacaran Period and surviving into the early Cambrian.”

Fossil of Stromatoveris psygmoglena, turned on its side.  New research suggests that Stromatoveris and related Ediacaran lifeforms could be among the earliest creatures that can be described as an animal. Ediacaran fossils have been found from Australia to arctic Siberia, Canada to southern Africa.  (Jennifer Hoyal Cuthill)

 

Dickinsonia is a genus of iconic fossils of the Ediacaran biota. While a bilaterian affinity had been previously suggested by some researchers, this study suggests that it is closely related to other members of the Ediacaran biota as well as Cambrian Stromatoveris.  (Jennifer Hoyal Cuthill)

 

More broadly, Hoyal Cuthill told me that “the story of the origin of life and the evolution of life are so interwoven.”

“Looking back as far as we can, we see important patterns emerging from the very start.  All things learn.  If possible, they add to complexity… And evolution does not result in a complete replacement.  When transitions happen -– even big ones – important life patterns continue.  And so do some creatures.”

This continuity within change is what she has focused on, in the transitional Proterozoic Eon when bacterial and plant life evolved into the more complex ocean animal life of the Cambrian explosion.

She has traveled the world and scoured the fossil record to come up with this conclusion:  that creatures that can be called “animals” existed at least as far back as the early days of the Ediacaran, some 630 million years ago, when many macro-fossils quite suddenly appeared following that early epoch of global freezing.

The Ediacaran period gets its name from the Ediacara Hills in Australia, where famous fossils of this age were found. Known also as the Vendian, the Ediacaran was the final stage of Pre-Cambrian time. During this time, large (up to meter-sized) organisms, often shaped like fronds with holdfast discs, lived on thick mats of bacteria which, unlike today, coated the sea floor. The slimy mats acted as a barrier between the water above and the sediments below, preventing oxygen from reaching under the sea floor and making it less habitable.

During this time, large (up to meter-sized) organisms, often shaped like discs or fronds,  lived on or in shallow horizontal burrows beneath thick mats of bacteria which, unlike today, coated the sea floor. The slimy mats acted as a barrier between the water above and the sediments below, preventing oxygen from reaching under the sea floor and turning it largely uninhabitable.

And then when the Cambrian explosion occurred beginning some 540 million years ago, most of those lifeforms were thought to have gone extinct. Some paleobiologists hold that Earth’s first mass extinction actually took place during this period, when newly evolved animals transformed the environment.

Biota from the Ediacaran period through the Cambrian explosion. (Proceedings of the Royal Academy; B M. Gabriela Mángano, Luis A. Buatois)

Hoyal Cuthill says that her research leads her to a very different view: that there was a broad but not mass extinction, and that Ediacaran animals survived well after the Cambrian Explosion.

And in the journal paper published this week, Hoyal Cuthill and co-author Jian Han of Northwest University in Xian present fossil evidence from southern China of Cambrian creatures that she argues are unquestionably animal.

She said they have characteristics such as radial symmetry, differentiated bodies and an animal type organization. These fossils date from the early Cambrian, she said, yet they are similar in important ways to creatures found during the earlier Ediacaran period.

In other words, this group of animals not only persisted from the onset of the Ediacaran period, but also after the often-invoked mass extinction that came along with the Cambrian Explosion.

Jennifer Hoyal Cuthill, paleobiologist with a focus on Ediacaran period when life began to grow substantially in size. (Julieta Sarmiento Photography).

Hoyal Cuthill says that while the fossil record from the Ediacaran is sparse, flora and fauna are known to have included some of the oldest definite multicellular organisms. The organisms, she said, resembled fractal fronds but bear little resemblance to modern lifeforms.

The world’s first ever burrowing animals also evolved in the Ediacaran, though we don’t know what they looked like. The only fossils that have been found are of the burrows themselves, not the creatures that made them.

In an earlier paper, she described how and why many of the Ediacaran lifeforms got as large as they did.

“All organisms need nutrients simply to survive and grow, but nutrients can also dictate body size and shape.

“During the Proterozoic, there seem to have been major changes in the Earth’s oceans which may have triggered this… growth to the macro-scale. These include increases in oxygen and, potentially, other nutrients such as organic carbon.”

In other words, the surrounding atmosphere, oceans, perhaps reversing magnetic fields, tectonic and volcanic activity and the resulting menu of chemical compounds available and climatic conditions are essential drivers of biological evolution.  Just as they are now considered some of the important indicators of a potentially habitable exoplanet.

And on a currently far more fanciful note, wouldn’t it be wonderful if scientists could some day not only find life beyond Earth, but to learn to study how that life, too, might have evolved.

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Diamonds and Science: The Deep Earth, Deep Time, and Extraterrestrial Crystal Rain

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Deep Earth diamond with garnet inside.  These inclusions, which occur during the diamond formation process, provide not only a way to date the diamonds, but also a window into conditions in deep Earth when they wee formed.  (M. Gress, VU Amsterdam)

We all know that cut diamonds sparkle and shine, one of the great aesthetic creations from nature.

Less well known is that diamonds and the bits of minerals, gases and water encased in them offer a unique opportunity to probe the deepest regions of our planet.

Thought to be some of the oldest available materials found on Earth — some dated at up to 3.5 billion years old — they crystallize at great depth and under great pressure.

But from the point of view of those who study them, it’s the inclusions that loom large because allow them to know the age and depth of the diamond’s formation. And some think they can ultimately provide important clues to major scientific questions about the origin of water on Earth and even the origin of life.

The strange and remarkable subterranean world where the diamonds are formed has, of course, never been visited, but has been intensively studied using a variety of indirect measurements.  And this field has in recent weeks gotten some important discoveries based on those diamond inclusions.

First is the identification by Fabrizio Nestola of the Department of Geosciences at the University of Padua and colleagues of a mineral that has been theorized to be the fourth most  common on Earth, yet had never been found in nature or successfully synthesized in a laboratory.  As reported in the journal Nature, the mineral is a variant of calcium silicate (CaSiO3), created at a high pressure that gives it a uniquely deep-earth crystal structure called “perovskite,” which is the name of a mineral, too.

Mineral science does not allow a specimen to be named until it has actually been found in name, and now this very common form of mineral finally will get a name. But more important, it moves forward our understanding of what happens far below the Earth’s surface.

 

 

Where diamonds are formed and found on Earth. The super-deep are produced very far into the mantle and are pushed up by volcanoes and convection  The lithospheric diamonds are from the rigid upper mantle and crust and the alluvial diamonds are those which came to the surface and then were transported elsewhere by natural forces. (Fabrio Nestola, Joseph R Smyth)

 

The additional discovery was of a tiny bit of water ice known as ICE-VII inside several other deep diamonds.  While samples of H2O ice have been identified in diamonds before, none were ICE-VII which is formed only under tremendous deep-Earth pressure.

In addition to being a first, the ICE-VII discovery adds to the growing confidence of scientists that much H2O remains deep underground, with some inferring as much deep subsurface water as found in the surface oceans.  That paper was authored by University of Nevada, Las Vegas geoscientist Oliver Tschauner and colleagues, and appeared in the journal Science.

Diamonds are a solid form of carbon with a distinctive cubic crystal structure.  They are generally formed at depths of 100 to 150 miles in the Earth’s mantle, although a few have come from as deep as 500 to 600 miles down.  (And some come from space, as described in this article below and in a just published Nature Communications article about diamonds in the Almahata Sitta meteorite that crashed in Sudan in 2006.)

Those super-deep Earth diamonds form in a cauldron up to 1,000 degrees F and at 240,000 times the atmospheric pressure at sea level.  They are made from carbon-containing fluids that dissolve minerals and replace them with what over time become diamonds.

Much more recently (tens to hundreds of million years ago), the would have been pushed to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites (blue-tinged in color and coarse grained) and lamproites (rich in potassium and also from deep in the mantle.)

The mantle – which makes up more than 80 percent of the Earth’s volume – is made of silicate minerals containing iron, aluminum, and calcium among others.  Blue diamonds are that color because of the presence of the trace mineral boron in the mantle.

And now we can add water the list as well.

 

Professor of Mineralogy Fabrizio Nestola presented on his recent work in advances in X-ray crystallography on diamonds and their inclusions in a talk title “Diamond, A Journey to the Center of the Earth.” One of his collaborators on the recent high-pressure calcium silicate paper is mantle geochemist Graham Pearson of the University of Alberta, where Nestola was recently a visiting professor. (RadioBue.it)

Nestola, who has been conducting his deep-Earth studies with a major grant from the European Union, is eager to take his already substantial work much further.

First he is looking for answers to the basic question of the origin of water on Earth (from incoming asteroids and comets or an integral component at formation) and ultimately to the origin of life.  Diamonds, he says, offer a pathway to study both subjects.

For water, his goal is to find a range of diamond-encircled samples that can be measured for their deuterium to hydrogen ratio — a key diagnostic to determining where in the solar system an object and its H2O originated,  Deuterium, or heavy hydrogen, is an isotope of hydrogen with an extra neutron.

An example of a super-deep diamond from the Cullinan Mine, where scientists recently discovered a diamond that provides first evidence in nature of Earth’s fourth most abundant mineral–calcium silicate perovskite. (Petra Diamonds)

As the number of diamond samples with evidence of water grows, Nestola says it will be possible to determine how the D/H ratio changes over time and as a result gain a better understanding of where the Earth’s water came from.

When it comes to clues regarding the origin of life, Nestola will be looking for carbon isotopes in the diamonds.

“Actually, it cannot be excluded that carbon from a primordial organic matter can even travel to the lower mantle,” he told me. “The oldest diamonds were dated 3.5-3.6 billion years, so it would be fantastic to detect a carbon isotope signature of surface carbon in a 3.5 billion years diamond.  This could provide very strong input for the origin of life.”

Regarding the high-pressure form of calcium silicate that he and his colleagues recently identified, Nestola said that many scientists have tried to reproduce it in their labs but have found there’s no way to keep the mineral stable at surface pressures.  So the discovery had to be made from inside the nearly impermeable container of a diamond.

The diamond that contained the common yet never before found mineral was just 0.031 millimeters across, is also a super-rare specimen.

Adding to the interest in this discovery is that other trace minerals and elements found in the inclusion strongly suggest that the material was once on the Earth’s crust.  The logic is that it would have been subducted as a function of plate tectonics billions of years ago, then encased in a forming diamond deep in the mantle, and ultimately sent back up near the surface again.

Most diamonds are born much closer to Earth’s surface, between 93 and 124 miles deep. But this particular diamond would have formed at a depth of around 500 miles, the researchers said.

“The diamond keeps the mineral at the pressure where it was formed, and so it tells us a lot about the ancient deep-Earth environment,” Nestola said.  “This is how we’ll learn about deep Earth and ancient Earth.  And we hope about those central origin questions too.”

 

A South African diamond crystal on kimberlite, an igneous rock formed deep in the mantle and famous for the frequency with which it contains diamonds. (Shutterstock)

For his ICE-VII study, Tschauner used diamonds found in China, the Republic of South Africa, and Botswana that had been pushed up from inside Earth.  He believes the range of locations strongly suggests that the presence of the ICE-VII is a global phenomenon.

Scientists theorize the diamonds used in the study were born in the mantle under temperatures reaching more than 1,000-degrees Fahrenheit.

“One essential question that we are working on is how much water is actually stored in the mantle.  Is it oceans, or just a bit?” Tschauner said. “This work shows there can be free excess fluids in the mantle, which is important.”

The mantle is a vast reservoir of mostly solid and very hot rock under immense pressure beneath the crust. It has an upper layer, a transition zone, and a lower layer. The upper layer has a little bit of water, but scientist estimate 10 times more water may be in the transition zone, where the enormous pressure is changing crystal structures and minerals seem to be more soluble. Minerals in the lower layer don’t seem to hold water as well.

There’s already evidence of water in the mantle in different forms, such as water that has been broken up and incorporated into other minerals. But these diamonds contain water frozen into a special kind of ice crystal. There are lots of different ways water can crystallize into ice, but ice-VII is formed under higher pressures.

While the diamond was forming, it must have encapsulated some liquid water from around the transition zone. The high temperatures prevented this water from crystalizing under the high pressures. As geologic activity moved the diamonds to the surface, they maintained the high pressures in their rigid crystal structures—but the temperature dropped. This would have caused the water to freeze into ice-VII.

The discovery of Ice-VII in the diamonds is the first known natural occurrence of the aqueous fluid from the deep mantle. Ice-VII had been found as a solid in prior lab testing of materials under intense pressure. As described before,  it begins as a liquid in the mantle.

“These discoveries are important in understanding that water-rich regions in the Earth’s interior can play a role in the global water budget and the movement of heat-generating radioactive elements,” Tschauner said.

This discovery can help scientists create new, more accurate models of what’s going on inside the Earth, specifically how and where heat is generated under the Earth’s crust.

 “It’s another piece of the puzzle in understanding how our planet works,” Tschauner said.

A polished and enlarged section of the Esquel pallasite meteoritemeteorite that delivered tiny nano-diamonds to Earth. This is a common occurrence, as there is believed to be substantial amounts of high-pressure carbon in the galaxies, and thus some diamonds. (Trustees of the NHM, London)

The diamonds studied by researchers such as Nestola and Tschauner not the sort that would ever go to the market.  “They are very bad diamonds, bad for jewelers,” Nestola said, “but precious for geologists.”

Diamonds are by no means exclusive to Earth, and are becoming a significant area of study for planetary exoplanet scientists, too.

Not only are they contained in minute form in meteorites, but atmospheric data for the gas giant planets indicates that carbon is abundant in its famous hard crystal form elsewhere in the solar system and no doubt beyond.

Lightning storms turn methane into sooty carbon which, as it falls, hardens under great pressure into graphite and then diamond.

These diamond “hail stones” eventually melt into a liquid sea in the planets’ hot cores, researchers told a an American Astronomical Society conference in 2013.

The biggest diamonds would likely be about a centimeter in diameter – “big enough to put on a ring, although of course they would be uncut,” says Dr Kevin Baines, of the University of Wisconsin-Madison and NASA’s Jet Propulsion Laboratory.

“The bottom line is that 1,000 tons of diamonds a year are being created on Saturn. People ask me – how can you really tell? Because there’s no way you can go and observe it.

“It all boils down to the chemistry. And we think we’re pretty certain.”

These potential raining diamonds, and all sorts of other extraterrestrial diamonds including possible diamond worlds, doubtless have their own scientifically compelling and important stories to tell.

 

 

 

 

 

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

To Understand Habitability, We Need to Return to Venus

Facebooktwittergoogle_plusredditpinterestlinkedinmail

This column was written by my colleague, Elizabeth Tasker.  Based in Tokyo, she is a scientist and communicator at the Japanese Space Agency JAXA and the Earth-Life Science Institute (ELSI).  Her book, “The Planet Factory,” was published last fall.


This image shows the night side of Venus in thermal infrared. It is a false-color image using data from the Japanese spacecraft Akatsuki’s IR2 camera in two wavelengths, 1.74 and 2.26 microns. Darker regions denote thicker clouds, but changes in color can also denote differences in cloud particle size or composition from place to place.  JAXA / ISAS / DARTS / Damia Bouic

“You can feel what it’s like on Venus here on Earth,” said Kevin McGouldrick from the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. “Heat a hot plate until it glows red, place your palm on its surface and then run over that hand with a truck.”

The surface of Venus is a hellish place. Suffocated by a thick atmosphere, pressure on the Venusian surface is 92 times greater than on the surface of Earth. Temperatures sit at a staggering 863°F (462°C), which is sufficient to melt lead.

The longest a spacecraft has survived in these conditions is a mere 127 minutes; a record set by the Russian Venera 13 mission over 35 years ago.

As the brightest planet in the night sky, Venus allured ancient astronomers into naming the world after the Roman mythological goddess of love and beauty. This now seems an ironic choice, but the contrast between distant observation and surface conditions produces an apt juxtaposition for exoplanets.

The comparison has led to an article in Nature Geoscience by McGouldrick and a nine author white paper advising on astrobiology strategy for the National Science Foundation. The conclusion of both publications echoes the irony of Venus’s name: we need to return to the inferno of Venus to understand habitable worlds.

 

A portion of western Eistla Regio is displayed in this three-dimensional perspective view of the surface of Venus. Synthetic aperture radar data from the spacecraft Magellan is combined with radar altimetry to develop a three-dimensional map of the surface. Rays cast in a computer intersect the surface to create a three-dimensional perspective view.  The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image, a frame from a video released in 1991, was produced at NASA’s JPL Multimission Image Processing Laboratory.

In the last 25 years, scientists have discovered over 3,500 extrasolar planets. The vast majority of these worlds have not been imaged directly, but are detected by tiny influences on their host star. These observations provide a measurement of the planet’s size and the average energy received from the star, but no details of the conditions at the planet surface. This leaves modern astronomers as blind to exoplanets as the ancient Romans were to the worlds of our solar system.

While we cannot visit the surface of exoplanets, our knowledge may be about to take a major leap forward. New instruments such as NASA’s James Webb Space Telescope (launch date 2019) and ESA’s Ariel mission (launch 2026) are aiming to detect the atmospheres of these distant worlds. The enveloping gases are a product of the planet’s geology, chemistry and biology, producing a direct indication of what is occurring on the surface.

However, this signature is hard to measure for terrestrial worlds with thin atmospheres, requiring a large number of precious observing hours. This means we need to select our telescope targets carefully. An ideal choice would be a planet writhing with geological and biological activity that is imprinting its presence in the atmosphere.

In short, what we want is an exo-Earth. What we don’t want is an exo-Venus.

Surface photographs from the former Soviet Union’s Venera 13 spacecraft, which touched down in March 1982. Ten probes from the Venera series successfully landed on Venus and transmitted data from the surface of the planet between 1961 and 1984. In addition, thirteen Venera probes successfully transmitted data from the atmosphere of Venus.

At first glance, a tantalizingly simple way to distinguish these two planets is the circumstellar habitable zone. Broadly defined, this is the region around a star where the radiation levels are right to support liquid water on a planet’s surface. At the inner edge of the habitable zone, water evaporates and is rapidly lost from the planet in a process known as ‘runaway greenhouse’. At the outer edge, carbon dioxide condenses into clouds and is unable to trap sufficient heat to prevent global freezing.

With a thick atmosphere lacking in water, Venus shows signs of having undergone a runaway greenhouse phenomenon that would seem to support the habitable zone edges. But digging a little deeper reveals more complex story. The habitable zone edges are traditionally calculated via climate models for the Earth. Yet, there is evidence that Venus was never that similar to the home planet we know.

While the Earth’s crust is broken into plates, Venus is thought to have a ‘stagnant lid’; a non-mobile crust that does not cycle material and nutrients up from the planet’s interior. Possibly linked with that —or maybe not— Venus has no magnetic field and would likely have suffered a similar fate to Mars and lost most of its atmosphere if it did not have such a thick reservoir of gases. There are almost certainly other differences; we don’t know because we haven’t been back to the Venusian surface since the 1980s.

What this means is that the path that led Venus to be an unimaginable inferno likely started a long time before a runaway greenhouse could occur.

If the deviation from Earth were initially driven by geodynamics, formation or other non-climate differences (such as the failure to form crustal plates, or poor internal heat circulation preventing a magnetic field) then the boundary between Earth and Venus is likely unrelated to the climate-based habitable zone. Without understanding the history of this second Earth-sized planet in our own system, we have no hope of differentiating between a Venus or Earth around another star.

A topographic map of Venus, with sinusoidal projection, based on data from the Magellan spacecraft, which was one of the few missions launched from the space shuttle.  It left for Venus in 1989 and mapped the planet until 1994.  (NASA)

But is this concern unnecessary? While an exo-Venus would not be an interesting place to hunt for signatures of life, we might learn about the formation of our two worlds by exploring the atmosphere of similar planets around other stars.

And this is where we hit a second problem; we don’t understand the atmosphere of Venus.

Models predict that planets that have undergone a runaway greenhouse should have an oxygen rich atmosphere. This is from evaporated water molecules that are broken apart by the ultraviolet radiation from the Sun, causing the constituent hydrogen atoms to escape the planet’s gravity while the heavier oxygen is left behind.  Venus’s atmosphere isn’t oxygen rich. It’s full of carbon dioxide and clouds of sulphuric acid.

This leaves us trying to understand the distant signature of alien atmospheres without a good comprehension of the examples we have in our own Solar System.

These arguments present a compelling case for Venus. Yet although three out of twelve proposals for NASA’s New Frontiers Program were for Venus missions, none were selected as finalists last December. The same was true for the last call for the Discovery Program; two out of five finalists for this lower cost mission category were for Venus, but neither were selected despite Discovery proposals being typically more focussed on the inner Solar System.

Kevin McGouldrick of the University of Colorado, Boulder, says the primary focus of his research is the nature and evolution of the clouds of Venus. Some 35 to 55 miles above the surface of Venus,  temperatures and pressures resemble those at the surface of the Earth.

Is there a reluctance to go to Venus?

Undoubtedly, planet surface conditions that can melt a spacecraft curbs enthusiasm. The insulation required to protect a probe on the Venusian surface or conduct a short mission will drive costs skyward and may seem a poor return compared to other projects.

Missions to study the Venusian atmosphere would be substantially less risky. The only mission currently operating around Venus is Japan’s Akatsuki orbiter, which last year returned data suggesting mountainous terrain on Venus was sufficient to drive waves through the huge weather system.

In his Nature Geoscience article, McGouldrick proposes that detailed monitoring of Venus’s atmosphere is needed to understand the planet’s history. “To find out why Venus is how it is now, we need to know how it used to be,” he pointed out.

This information could be found in the abundances and isotopes (different variations of the same element) of the noble gases on Venus. These unreactive elements are acquired during planet formation, so changes in their quantities indicate losses in Venus’s past of strippable quantities such as atmosphere and water. Comparison with Earth can also indicate if the two planets formed from similar materials, or if part of the dichotomy between these Earth-sized worlds can be laid at the door of compositional differences.

But another orbiter loses out on basic appeal. NASA planetary exploration typically follows the pattern of fly-by spacecraft, orbiters, landers and rovers and then missions to return samples to Earth. Mars exploration is following this list, with the planned Mars 2020 mission collecting samples for possible later collection. Missions to Europa and Mercury are doing the same, albeit at an earlier stage.

But the hellish surface conditions of Venus make this pattern difficult, and the prospect of repeating the orbiter step with better instruments is significantly less enticing.

The solution might be a combined orbiter and lander mission, with data from the orbiter mitigating the risk associated with the lander. Alternatively, an aeroplane or balloon that travels through the upper parts of the Venusian atmosphere might combine originality with data that cannot be achieved in orbit. Designs like these have been proposed for a Russia-led mission with a contribution from NASA, known as Venera-D, but funding remains uncertain.


This image of the equatorial region of Venus taken by the Japanese Akatsuki probe provides striking detail of the equatorial, tropical, and extra-tropical clouds of the planet. Color changes indicate local variations in the amounts of a little-understood ultraviolet absorber and sulfur dioxide in the atmosphere. JAXA / ISAS / DARTS / Damia Bouic

While a Venus mission did not make into the finalists for the New Frontiers program, funding was given to develop a camera that could measure the mineralogy and composition of Venus’s rocks. This demonstrates a continual interest by mission experts in Venus, but publications by the community suggest this needs to be higher up the priority list.

The bottom line is that visiting our neighbor may present one of the biggest challenges in the Solar System. But exoplanet research may be lost without it.

Facebooktwittergoogle_plusredditpinterestlinkedinmail

2.5 Billion Years of Earth History in 100 Square Feet

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Scalding hot water from an underground thermal spring creates an iron-rich environment similar to what existed on Earth 2.5 billion years ago. (Nerissa Escanlar)

Along the edge of an inlet on a tiny Japanese island can be found– side by side – striking examples of conditions on Earth some 2.4 billion years ago, then 1.4 billion years ago and then the Philippine Sea of today.

First is a small channel with iron red, steaming and largely oxygen-free water – filled from below with bubbling liquid above 160 degrees F. This was Earth as it would have existed, in a general way, as oxygen was becoming more prevalent on our planet some 2.4 billion years ago. Microbes exist, but life is spare at best.

Right next to this ancient scene is region of green-red water filled with cyanobacteria – the single-cell creatures that helped bring masses of oxygen into our atmosphere and oceans.  Locals come to this natural “onsen” for traditional hot baths, but they have to make their way carefully because the rocky floor is slippery with green mats of the bacteria.

And then there is the Philippine Sea, cool but with spurts of warm water shooting up from below into the cove.

All of this within a area of maybe 100 square feet.

It is a unique hydrothermal scene, and one recently studied by two researchers from the Earth-Life Science Institute in Tokyo – evolutionary microbiologist Shawn McGlynn and ancient virus specialist Tomohiro Mochizuki.

They were taking measurements of temperature, salinity and more, as well as samples of the hot gas and of microbial life in the iron-red water. Cyanobacterial mats are collected in the greener water, along with other visible microbe worlds.

Shawn McGlynn, associate professor at the Earth Life Science Institute in Tokyo scoops some iron-rich water from a channel on Shikine-jima Island, 100 miles from Tokyo. (Nerissa Escanlar)

The scientific goals are to answer specific questions – are the bubbles the results of biology or of geochemical processes? What are the isotopic signatures of the gases? What microbes and viruses live in the super-hot sections? And can cyanobacteria and iron co-exist?

All are connected, though, within the broad scientific effort underway to ever more specifically understand conditions on Earth through the eons, and how those conditions can help answer fundamental questions of how life might have begun.

“We really don’t know what microbiology looked like 2.5 billion or 1.5 billion years ago,” said McGlynn, “But this is a place we can go where we can try to find out. It’s a remarkable site for going back in time.”

In particular, there are not many natural environments with high levels of dissolved iron like this site. Yet scientists know from the rock record that there were periods of Earth history when the oceans were similarly filled with iron.

Mochizuki elaborated: “We’re trying to figure out what was possible chemically and biologically under certain conditions long ago.

“If you have something happening now at this unusual place – with the oxygen and iron mixing in the hot water to turn the water red – then there’s a chance that what we find today was there as well billions of years ago. ”

Tomohiro Mochizuki at collecting samples directly from the spot where 160 degree F water pushes up through the rock at Jinata hot spring. (Nerissa Escanlar)

The Jinata hot springs, as the area is known, is on Shikine-jima Island, one of the furthest out in the Izu chain of islands that starts in Tokyo Bay. More than 100 miles from Tokyo itself, Shikine-jima is nonetheless part of Tokyo Prefecture.

The Izu islands are all volcanic, created by the underwater movements of the Philippine and Pacific tectonic plates. That boundary remains in flux, and thus the hot springs and volcanoes. The terrain can be pretty rugged: in English, Jinata translates to something like Earth Hatchet, since the hot spring is at the end of a path through what does look like a rock rising that had been cut through with a hatchet.

Hot springs and underwater thermal vents have loomed large in thinking about origins of life since it became known in recent decades that both generally support abundant life – microbial and larger – and supply nutrients and even energy in the form of electricity from vents and electron transfers from chemical reactions.

And so not surprisingly, vents are visited and sampled not infrequently by ELSI scientists. McGlynn was on another hydrothermal vent field trip in Iceland over the summer with, among others, ELSI Origins Network fellow Donato Gionovelli and ELSI principal investigator and electrochemist Ruyhei Nakamura..

McGlynn’s work is focused on how electrons flow between elements and compounds, a transfer that he sees as a basic architecture for all life. With so many compelling flows occurring in such a small space, Jinata is a superb laboratory.

The volcanic Izu island chain, starting in Tokyo Bay and going out into the Philippine Sea.

For Mochizuki, the site turned out to be exciting but definitely not a goldmine. That’s because his speciality is viruses that live at very high temperatures, and even the bubbling hot spring in the iron trench measured about 73 degrees C (163 degrees F.) The viruses he incubates live at temperatures between closer to 90 C (194 F), not far from the boiling point.

His goal in studying these high-temperature (hyperthermophilic) viruses is to look back to the earliest days of life forming on Earth, using viruses as his navigators. Since life is thought by many scientists to have begun in a super hot RNA world, Mochizuki wants to look at viruses still living in those conditions today to see what they can tell us.

So far, he explained, what they have told us is that the RNA in the earliest lifeforms on Earth – denizens of the Archaean kingdom – did not have viruses. And this is puzzling.

So Mochizuki is always interested in going to sample hot springs and thermal vents to collect high temperature viruses, and to look for surprises.

Though the bubbling waters were so hot that both researchers had difficulty standing in the water with boots on and holding their collection vials with gloves, it was not hot enough for what Mochizuki is after. But that certainly didn’t stop him from taking as many samples as he could, including some for other ELSI researchers doing different work but still needing interesting samples.

Researchers often need to be inventive on field trips, and that was certainly the case at Jinata. When McGlynn first tried to sample the bubbles at the scalding spring, his hands and feet quickly felt on fire and he had to retreat.

To speed the process, he and Mochizuki built a funnel out of a large plastic water bottle, a device that allowed the bubbles to be collected and directed into the sample vial without the gloved hands being so close to the heat.   The booted feet, however, remained a problem and the heat just had to be endured.

Nearby the steaming bubbling of the hot spring were collections of what appeared to be fine etchings on the bottom of the red channel. These faint designs, McGlynn explained, were the product of a microbe that makes it’s way along the bottom and deposits lines of processed iron oxide as it goes. So while the elegant designs are not organic, the creatures that creates them surely is.

“Touch the area and the lines go poof,” McGlynn said. “That’s because they’re just the iron oxide; nothing more. Next to us is the water with much less iron and a lot more oxygen, and so there are blooms of (green) cyanobacteria. Touch them and they don’t go poof, they stick to your hand because they’re alive.”

Filaments created by microbes as they deposit iron oxide at the bottom of small channel. (Marc Kaufman)

McGlynn also collects some of the the poofs to get at the microbes making the unusual etchings. It may be a microbe never identified before.

As a microbiologist, he is of course interested in identifying and classifying microbes. He initially thought the microbes in the iron channel would be anaerobic, but he found that even tiny amount of oxygen making their way into the springs from the atmosphere made most aerobic, or possibly anaerobes capable of surviving with oxygen (which usually is toxic to them.)

He also found that laboratory studies that found cyanobacteria would not flourish in the presence of iron were not accurate in nature, or certainly were not accurate at Jinata onsen.

But it is that flow of electrons that really drives McGlynn – he even dreams of them at night, he told me.

One of the goals of his work, and that of his colleague and sometimes collaborator at ELSI, geobiochemist Yuichiro Ueno, is to answer some of the outstanding questions about that flow of electrons (electricity) from the core of the Earth. The energy transits through the mantle, to the surface and then often is in contact with the biosphere (all living things) before it enters the atmosphere and sometimes disappears into space.

He likened the process to the workings of a gigantic battery, with the iron core as the cathode and the oxygen in the atmosphere as the anode. Understanding the chemical pathways traveled by the electrons today, he is convinced, will tell a great deal about conditions on the early Earth as well.

It’s all important research in what is a chipping away of the many unknowns in the stories of the origins of Earth and the origin of life.

A boundary between where the very hot iron-rich water meets and the less hot water with thriving cyanobacteria colonies at Jinata.

The field work also illustrated the hit-and-miss nature of these kind of outings. While McGlynn has not come up with Jinata surprises or novel understandings, he was so taken with the setting that he wondered if a seemly empty building not too far from the site could be turned into an ELSI marine lab.

And while Mochizuki did not find sufficiently hot water for his work, he might still be coming back to the island, or others nearby. That’s because he learned of a potentially much hotter spring at a spot where the sea hits one of the island’s steep cliffs – a site that requires boat access that was unsafe in the choppy waters during this particular visit.

In addition, McGlynn and Mochizuki did make some surprising discoveries, though they didn’t involve microbes, electron transfer or viruses.

During a morning visit to a different hot spring, they came across a team of what turned out to be officials of the Izu islands – all dressed in suits and ties. They were visiting Shikine-jima as part of a series of joint islands visit to assess economic development opportunities.

The officials were intrigued to learn what the scientists were up to, and made some suggestions of other spots to sample. One was an island occupied by Japanese self-defense forces and generally closed to outsiders. But the island is known to have areas of extremely hot water just below the surface of the land, sometimes up to 100 C (212 F.)

The officials gave their cards and told the scientists to contact them if they wanted to get onto that island for sampling. And as for the official from Shikine-jima, he was already thinking big.

“It would be a very good thing,” he said, “if you found the origin of life on our island.

Facebooktwittergoogle_plusredditpinterestlinkedinmail