Category Archives: The (really) Ancient Earth

Ediacara; Welcome to the revolutionary world of animals

Mistaken Point on the Atlantic coast of Newfoundland (Canada) acquired its unfortunate reputation by fooling mariners.  In a celebration of a different kind, UNESCO, in July 2016 designated the Mistaken Point coast a World Heritage Site; it is the graveyard of exquisitely preserved animals known as the Ediacaran Fauna, and at 575 million years they are the oldest known, structurally complex, multicellular creatures.

From an evolutionary context, life forms during the previous 3 billion years were dominated by much simpler algal-bacteria like organisms that constructed mats, mounds and columns (stromatolites) and even reef-like structures, all made by single-cell prokaryotes.  The Ediacaran fauna thus represents a kind of evolutionary paradigm shift – to real animals.  As Guy Narbonne (Queens University, Ontario) has suggested, this unique fauna probably formed the “root stock” of the more recent and familiar animal kingdom, but also includes some fossils that represent failed evolutionary experiments – creatures having unique form, phylum, and genetic codes that simply didn’t go anywhere.

The complete 2016 Mistaken Point UNESCO Heritage Site dossier by Richard Thomas and Guy Narbonne can be found here, but NB, it is a large file!

What kind of animals were they?

Although discovered in Namibia, the age and evolutionary significance of the fauna were first recognised in Flinders Range strata, Australia. The name Ediacara is probably Aboriginal.  Ediacaran fossils range from 575-542 million years; the period immediately prior to what is commonly called the Cambrian Explosion. Ediacaran fossils are now found on all continents except Antarctica.

The iconic Ediacaran fossils are those that appear petal-, feather-, or sea-pen-like, creatures that in some beautifully preserved examples exhibit complex growth patterns. Guy Narbonne has described these growth patterns as “quilted fractals”, an analogy that is quite apt. They were soft-bodied animals; fossils with hard parts, shells or hard skeletal frames did not appear until the very end of the Precambrian, becoming abundant in the Cambrian.  The petal-like structures had a central stem that was attached to or grew into the sea floor; in some cases only these holdfasts are preserved. Other forms that appear frond-like grew to almost 2m in length. Some were fan-, bush-, and comb-shaped; others simple domes or discs. Imagine the ancient seafloor covered in a forest of these soft, delicate forms, swaying in the wash of gentle sea currents.  It must have been quite stunning.

Trace fossils are also present, becoming abundant in rocks younger than about 555 million years.  These are not static impressions of animals, but tracks and burrows of worm-like creatures that moved on or through soft sediment.  Many traces resemble those made by animals in much younger strata, and if the same interpretation is applied to the Ediacaran types, then they too represent animal behaviours such as feeding, or burrowing a new home.

 

Preservation – an interesting conundrum

Paleontologists frequently consider the preservation potential of the fauna and flora they study.  Animals having hard parts are more likely to be preserved than those without.  However, even skeletal remains may not survive the vagaries of scavenging or dislocation.  Complete dinosaur skeletons, although celebrated, are rare; after death the animal is prone to being eaten, crunched by powerful jaws, or dismembered by flooding rivers. Preservation of soft-bodied animals is even more fraught – they tend to decay rapidly, are eaten by scavengers, or are dismembered by ocean currents and waves.

Most Ediacaran fossils were preserved as impressions in sediment. The uniqueness of the Ediacaran fossil record is a testimony to the absence of scavengers during this geological period.  Many, like the Mistaken Point communities (and also in Mackenzie Mountains) lived in relatively deep water where currents were subdued but strong enough to ensure a continuous supply of nutrients.  That the fossils are intact means that they were buried by sediment before decay set in.

Those animal communities that lived in shallower seas (there are examples in Australia, Namibia and Russia) were periodically subjected to stronger currents and waves and had correspondingly lower preservation potential.  The buried parts of stems and fronds, and some animal burrows could be preserved (after all they were already buried), but the more delicate structures above the sea floor were easily broken up.   In some environments, such as those now found in the Flinders Range, the dead fronds or bushes were covered by a thin microbial mat that enhanced preservation.  Elsewhere (Newfoundland and England), volcanic ash falling into the sea filtered quickly through the water column, gently smothering the live animals – a bit like Pompeii.

In the grand scheme of things It is generally understood that complex, multicellular animals like the Ediacara fauna require oxygen.  For much of the preceding 3 billion years, free oxygen was in short supply. By about 1800 million years the oxygen levels are thought to have been about 10% of the concentration in our modern atmosphere (based mainly on stable isotope chemistry).  The biomass back then was dominated by single cell, prokaryotic microbes (such as cyanobacteria).  There is good evidence that simple, multicell eukaryotes were present at least 1300 million years ago, for example in forms like red algae, but they were in the minority. Sudden appearance of the Ediacaran fauna indicates that oxygen levels may have increased abruptly 600-580 million years ago, creating the right conditions for evolutionary expansion; some estimates put oxygen concentrations at about 50% present atmospheric levels.

Continued research will probably refine these numbers. Regardless, the Ediacaran fauna provides fantastic evidence of significant evolutionary trajectories and ancient environmental conditions for one of the most crucial periods in the history of our earth.

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A Watery Mars; Canals, a duped radio audience, and geological excursions

Deceptive news is the art of pulling wool over the eyes of the populace, a tool (recently resurrected by certain politicians) for persuasion or dissuasion.  Orson Welles got more than he bargained for when, on October 30, 1938, he orchestrated a radio adaptation of H.G. Wells The War of The Worlds, a 1898 sci-fi that pits intelligent Martians against Victorian Britain.  Welles broadcast created a mix of amusement in some commentators, and in others panic and anger; panic in the unwitting, anger in the duped (especially other broadcasters), and amusement in all the above.

Well’s novel, apart from being the product of an agile mind, was influenced by some of the popular astronomical ideas of his time.  Italian astronomer Giovanni Schiaparelli produced, in 1888 a wonderfully detailed map of Mars showing (above image), among features such as seas, islands, and other landmasses, a network of ‘canali’, or channels.  Canali was misinterpreted in English as canals, and along with all its connotations of intelligent life, the idea of Martian canals entered popular belief.

Were the anthropomorphic connotations of the word canali deliberate?  Percival Lowell, a self-made American astronomer certainly thought so.  In 1894 Lowell announced his own findings, that there were indeed canals, 100s of them, many of them straight, intricately networked, and all artificial, which of course meant intelligent beings.  H.G. Wells simply expanded Lowell’s ideas to the point of delightful absurdity.  That O. Welles would later foist his version of events on an unsuspecting public seems quite reasonable.

Since the 1970s we have been projecting our own intelligence and sense of puzzlement on Mars, using satellites and landed vehicles.  There are no artificial canals, but there are canyons, channels and gullies, landforms that bear an uncanny resemblance to terrestrial analogues.  There is now a significant body of evidence to indicate that Mars was once watery.

On earth, sediment is distributed far and wide by flowing water. Very fine sediment from rivers or wind-blown dust is commonly suspended in water; the sediment gradually settles on the sea or lake floor.  Coarser sediment, like sand and gravel tends to be ‘entrained’ close to the sea floor or river bed by fast flowing water.  Sediment that is moved in this way forms a variety of structures such as ripples and larger dune-like structures.

Rivers in particular, generally move sediment to larger repositories, or basins such as seas or lakes; The kinds of landforms that represent these processes are very distinctive.  On Mars, there are several landform-indicators of flowing liquid (most likely water), most of which have direct terrestrial counterparts; deltas, straight and meandering river, point bars, alluvial fans, and gullied crater margins.  One such Martian landform, imaged by NASA’s Mars Global Surveyor, is the Eberswalde Delta which contains many of the ingredients that also make up terrestrial deltas.  In this case, sediment making up the delta was probably derived from outside the Eberswalde Crater and subsequently transported by rivers into the crater:

  • The delta consists of one or two main river channels (left side) that split into many smaller channels,
  • Bifurcating channels form distinct lobes – there are at least 6 of these, where each lobe represents a specific period of delta formation.
  • Switching of delta lobes is common in terrestrial delta. Each lobe represents a period of sediment movement and deposition, in this case into the deep crater basin.  At a certain point in time, the channel will switch direction and begin to build a new lobe.
  • Each new lobe partly overlaps older lobes, such that the younger deposits appear to lie on top of older deposits.
  • The Lena Delta in Russia provides a nice analogue for the overall shape of channels, with some active parts of the delta (especially the centre-right) juxtaposed with less active segments.

The Eberswalde Delta has another remarkable set of structures.  Meander loops (opposite image), seemingly identical to those seen in meandering rivers on Earth, contain patterns of progressive channel movement.  The Martian meander channel loop was eventually cut off, perhaps forming an oxbow lake like its terrestrial counterpart.

Martian landforms like these are mostly found in regions assigned to the Noachian Period, a geological interval that extended from 4.1 to 3.7 billion years.  All the evidence (so far) points to a time when surface water was common as rivers, lakes, and possibly seas; groundwater can be added to this mix.  If this was the case, there must also have been water vapour in the atmosphere.  The surface must have been significantly warmer than the present frigid temperatures; water vapour probably provided some degree of greenhouse protection.  Overland flow of water also produced sediment, much of which ended up in impact craters and broad lowlands.

 

However, some extremely large outflow channels, such as the Kasei Valles formed sporadically during a later, generally drier and colder time known as the Hesperian Period (3.7 to 2.9 billion years).  This massive system of channels and canyons extends about 3000km from its source in the Tharsis volcanic region, and through about 4km of topographic relief. The overall form of the channels, plus more detailed images of flow-like structures within the channels, indicates possible catastrophic outbursts of humongous volumes of water.  One popular hypothesis to account for this involves massive volumes of frozen groundwater being released either during meteorite impact or volcanic activity and heating.

The comparison between Eberswalde Delta and Kasei Valles mega-floods is quite stark; the delta represents relatively continuous river flow over a long period of time, into a crater.  The Kasei Valles outflow formed almost instantly, driven by the forces of impact and directed away from the crater.

Scientific understanding of Martian geology will continue to evolve; some hypotheses will stand the test of experimental and observational rigour; others will become history.  Modern science has developed the technology to actually do the field work, albeit remotely.  Perhaps we shouldn’t be too hasty to consign Schiaparelli’s and Lowell’s ideas to the theatrically amusing; their observations and explanations were not without context. Keep in mind the possibility that another H.G. Wells may point a satirical finger at 21st century science.

NASA, ESA and other organizations have multiple sites to access imagery and general information on all space missions.  SEPM (Society for Sedimentary Research) also has a Special Publication (number 102; 2012) with 12 papers that describe aspects of sediments and sedimentary rocks on Mars.  The Introductory chapter by John Grotzinger and Ralph Milliken provides an excellent technical summary of the Martian sedimentary realm.

 

 

 

 

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Sand dunes but no beach; a Martian breeze

When James Hutton, in 1785 presented to the Royal Society of Edinburgh his ideas on the uniformity of earth processes (over vast tracts of time), he did so with both feet planted firmly on good Scottish ground.  Hutton’s Principle, for which Archibald Geikie later (1905) coined the phrase “The present is the key to the past” gave to geologists a kind of warrant to interpret the geological past using observations and experiments of processes we see in action today (see an earlier post for a bit more discussion on this philosophy).  One wonders whether either of these gentlemen gave thought to the Principle being used to interpret processes elsewhere in our solar system.

There is of course, no logical reason why we cannot use terrestrial environments and physical-chemical-biological processes to unravel the geology on our solar neighbours.  We may need to extend our thinking beyond purely earth-bound processes, but the Principle remains a starting point for scientific thinking, interpretation, and discovery.  Mars provides the perfect opportunity for this scientific adventure.

I am constantly amazed with the images that various satellites and extraterrestrial vehicles provide of our celestial neighbours.  The surface of Mars is no exception.  There is clear evidence for ancient processes involving water; landforms and landscapes, strata, and minerals, all pointing to a once-watery planet – ancient rivers, lakes, and seas, beset by Noachian floods.  But all this aqueous excitement was in the distant past; more than 3.7 billion years past.  The Martian surface is now cold and bone dry (although the solid carbon dioxide ice does melt from time to time).  Active surface processes on Mars, i.e. those operating now, mainly involve loose sediment (sand, dust), and wind.  On earth, our experience tells us that if there is enough wind and enough sand, then sand dunes will form. Martian sand dunes look pretty much like our earth varieties.

The formation of terrestrial ripples and dunes requires certain (well understood) sediment attributes and physical processes.  We define sand grains as particles of rock or mineral that range in size from about 0.1mm to 2mm diameter.  Most dunes and ripples on earth form in sands that are in the 0.1mm to 0.3mm range.

  • The sand needs to be dry.
  • Sand grains must be loose, and not stick to one another (in technical jargon they are cohesionless).
  • Wind speed must be greater than the threshold for moving the grains. Stronger winds can move larger grains.

Satellite imagery of the Martian surface has revealed that sand dunes and ripples are common. They have formed, and continue to form in crater floors, broad flat plains, and ancient river valleys; basically anywhere there is sufficient loose sand available.

The variety of dune sizes and shapes is similar to that seen on earth.  Dune shape, like the Barchan dunes shown in the above images, provides clues to prevailing wind directions.  Other dune forms suggest greater variability in wind direction and strength, like the smaller, ripple-like structures (below) imaged by Curiosity ; here, changes in wind direction and speed are indicated by the very small ripples that move in different directions across the larger structures.  These patterns of sand movement are identical to those we commonly see on earth.

The larger dune imaged by Curiosity (below) is moving directly towards the camera.  Sand blown over the top of the dune (the crest) tumbles or slides down the steep front, or lee face, a process that continues as the dune moves forwards.  The inset, taken with a special camera that acts like a small magnifying glass (or hand lens), shows that the sand grains are indeed loose and cohesionless.

All the above images show dunes and ripples that are currently active.  It is also possible to identify fossil dunes in much older strata, using structures within the rocks.  In the examples below, the Martian fossil dune structures are very similar to those we see in some familiar rocks at Zion National Park (Utah).  The kind of layering visible in both Martian and earth examples is called crossbedding (see here for an explanation of how crossbedding forms).

Despite the obvious similarities between Martian and Terrestrial dunes, one in-depth analysis has led a couple of researchers (Gary Kocurek and Ryan Ewing, see below) to suggest that there are also important differences.  The Martian atmosphere is much less dense than that on Earth; there is no oxygen or water vapour.  Mars is consistently much colder; permafrost is probably widespread but in this case the ice is solid carbon dioxide.  Even if the CO2 melts, it will sublime (to gas) rather than form a liquid.  In some cases, permafrost may even stabilise, or solidify dunes.

One important difference between Earth and Mars is in the availability of loose sand.  On earth, much sand is produced by weathering of rock, by all the elements of weather plus chemical reactions that commonly involve oxygen.  Sand is available along most ocean, lake and river shores.  On Mars, physical weathering is very slow; sand is no longer moved by water, as it is on Earth.  Chemical weathering on Mars is also extremely slow.  Thus, the only sand available will likely be from local permafrost melt, the very slow breakdown of rocks, and the occasional meteorite impact.  Some sand may be left over from the period on Mars when water was abundant, the Noachian Period 4.1 to 3.7 billion years ago, but that seems like an awfully long time for sand grains to hang around.

Fossil dunes on Mars, like those on earth, provide clues to the kinds of environments that once existed. Some of these very ancient dunes may even have been associated with Martian lakes and seas.  Modern, active dunes on Mars have little or no association with water.  But they do provide information on sediment availability, wind direction, and wind strength.  The latter may be important when deciding where to locate future sites for human habitation.

NASA, ESA and other organizations have multiple sites to access imagery and general information on all space missions.  SEPM (Society for Sedimentary Research) also has a Special Publication (number 102; 2012) with 12 papers that describe aspects of sediments and sedimentary rocks on Mars.  The paper by Kocurek and Irwin, cited above, is one of these papers.

Kocurek and Ewing, 2012.  Source-to-sink; an Earth/Mars comparison of boundary conditions for eolian dune systems, p. 151-168.

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Comets; portents of doom or icy bits of space jetsam?

Omens, God’s wrath, or just plain misfortune; comets were seen by our Medieval forebears as a disturbance in the natural state of the heavens, portending disaster, pestilence, or famine, and if you were really unlucky, all three.  Harold, Earl of Wessex and later King, before he did battle against William of Normandy in 1066, must have had some misgivings with Halley’s comet nicely lighting up the northern sky (we now know it was comet Halley); he probably should have kept both eyes on the battle. Portent indeed; the Norman conquest changed irrevocably the history of Britain.

It seems that the ancient Chinese were a little more rational in their deliberations on comets – they referred to them as brush stars, and as early as 613 BC were computing approximate orbits.  In fact it is ancient Chinese astronomy records that have enabled modern astronomers to confirm calculated orbit periodicities for comets like Halley. Continue reading

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Darwin Day, with apologies to Abraham Lincoln

February 12 is Darwin Day.  On this day in 1809 Abraham Lincoln was also born. Lincoln rose from his humble beginnings in Kentucky to become the 16th President of the Union, but almost immediately was plunged into a brutal Civil War.  His legacy is tied to the War, the Emancipation Proclamation, and his address at what was left of Gettysberg on November 19, 1863. Darwin’s legacy could not be more different; bold statements about curiosity and creativity, and one of the greatest revolutions in scientific thought. Continue reading

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The (not so) Great Dying; Permian extinctions

It seems that global catastrophes and the ensuing mass extinction of all manner of life-forms, asteroid impacts and Dinosaurs immediately come to mind, were made for Popular Science.  Even Hollywood is in on the act.  Perhaps it’s because, in the telling, they appeal to some innate sense of nihilism, a bit like the existential threats that politicians trot out from time to time.

A recent scientific paper by Steven Stanley published by the US National Academy of Sciences, provides some good news on this score; past estimates of life forms snuffed out by such global events, have been exaggerated.  Stanley’s reassessment accounts for the fact that extinctions are taking place all the time, in the background, and that these individual, long-term biotic events need to be subtracted from the total species loss resulting from some catastrophe.  For example, in the normal course of evolution, species are continually evolving and in doing so may create environmental pressures within their niche wherein other species are unable to compete; they may be eaten, or their food source disappears.   They gradually die off.  We certainly know this to be the case in our modern world, where human-caused extinctions are legion.  A case in point is the extinction event at the end of the Permian period (299-252 million years ago), morbidly referred to as the Great Dying.  Up to 96% of species were deemed to have disappeared, which also means that there were not a lot left to carry on the evolutionary journey towards the modern world.  Stanley’s estimates, taking background extinctions into account, now put this at 81% – still catastrophic, but not as bad as we once thought.

 

The (not so) Great Dying

Geological Periods are intervals of time past, for which we now have a record measured in rocks.  The beginning or end of a period is commonly defined by abrupt changes in fossils – we don’t need to know what caused these abrupt changes in life forms, only that such changes occurred.  Two well-known examples are the Cambrian (beginning 542 million years ago) where complex, multicellular animals with preservable hard parts (skeletons, shells) first appear. The end of the Cretaceous Period marks the demise of dinosaurs, although it seems the dinos were already in decline – the asteroid impact merely hastened their demise.

The Permian is also marked by a huge, and apparently abrupt loss of species, some groups lost forever.  The Great Dying was probably one of the most catastrophic extinction events ever recorded, greater even than the aftermath of the asteroid that plummeted to earth 65 million years ago.  Rugose corals disappeared altogether (image of some examples at the top of the page); 50-60% of plankton, and 60% of bivalve species became extinct.  Clearly some species survived and continued to evolve, otherwise we would not today enjoy bouillabaisse or clam chowder.

 

Suffocation or acid indigestion?

Illuminating the possible causes for this event has produced some interesting, even creative explanations; asteroid impact, widespread volcanism, acid rain and acidic oceans, air and sea temperature increases, algal blooms, plate tectonic assembly of a supercontinent, climate change, and even a supernova.  In many respects all (except the supernova) may be related.  Back in the Permian, the distribution of continents and oceans looked nothing like it does today.  By about 300-270 million years ago, two very large continental blocks, Gondwana and Laurasia, had combined to form the supercontinent Pangea (or Pangaea).  Pangea was surrounded by the global ocean Panthalasa.  The supercontinent began to break apart about 200 million years ago (here is a USGS animation of this process).

 

The end of the Permian is marked by another remarkable event.  Humungous volumes of basalt were erupted over (what is now) the Siberian Platform – the Siberian Traps.  At least 3 million km3 of lava were erupted. Putting this number in context, Mt St Helens produced about 1 km3 of lava during the 1980 eruption; the entire island of Kilauea (Hawaii) is about 25,000-30,000 km3.  The Siberian eruptions lasted about 800,000 years.  One of the by-products of volcanic eruptions is the release of gases, mostly water vapour, but also carbon dioxide (CO2) and sulphur dioxide (SO2).  The volume of CO2 released to the atmosphere over such an extended period of time must have been huge.  Both the eruptions and evolution of CO2 are currently regarded as a likely cause of the mass extinction.

Addition of so much CO2 into the air has a number of consequences.  Many species of land-based plants don’t do so well , especially in more acidic rain. Carbon dioxide also dissolves easily and rapidly in sea water, and at some point in this process, the buffering capacity of sea water (namely its ability to prevent runaway changes in acidity or alkalinity) is over come and the pH decreases (acidity increases) to the point where many animals and plants find it difficult to eke out a living.

However, certain algae can thrive in such conditions; algal blooms tend to remove oxygen from water, exacerbating already intolerable living conditions for most other species.  One hypothesis, proposed in 2013, involves microbes that metabolize carbon in the oceans, turning it into methane; the authors in this paper argue that it was bursts of methane, not CO2, that created greenhouse gas conditions and effectively poisoned the atmosphere.

 

Is there a disconnect between the timing of extinction and these hypotheses?

Precise dating of zircon crystals in beds of sedimentary rock that straddle the extinction event, indicate that it may have taken place extremely rapidly; no more than 60,000 years that, in geological terms, is really fast. The results of this study by Seth Burgess and colleagues were published in 2014 (Open Access).  There is also evidence, cited in this paper, that changes to the carbon cycle were already underway when the extinction began, including possible ocean acidification and increased temperatures.  However, the Siberian Trap eruptions lasted some 800,000 years.  Were the basalt eruptions solely responsible for the extinction; was there a particularly vigorous period of eruption within the 800,000 years that helped trigger the mass die-off?  Another proposal, that an asteroid impact may also have played a role, has not been entirely put to bed.  The authors of a 2001 publication claim to have detected extraterrestrial helium and argon (i.e. the kind found in meteorites) in carbon crystals (fullerenes).  However, there appears to be some dispute over this discovery, and the existence of such an impact is still poorly verified.

 

Postscript

The terminal Permian extinction continues to hold fascination for scientists of all stripes.  This fascination extends beyond the event itself; clearly there was recovery of biota.  Perhaps this attests to the power of evolutionary processes, when in a single event more than 80% of species are eradicated, but we end up with the remarkable diversity of life in our modern world (interrupted by at least one more bolide).  Best we look after it all.

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Extreme living conditions; the origin of life and other adventures

Extreme events are fascinating.  Extreme sports may give us a kind of vicarious thrill, at least until something goes awry at which point we might comment about the foolishness of the act.  Extremes in the natural world are the stuff of movies; asteroids, tsunamis, tornadoes, plagues.  Perhaps our morbid fascination with such events derives from the realization that they can be real.

Over the last 2-3 decades, science too has developed a fascination for extreme living, for creatures that happily thrive in conditions that most other life forms, including us, would find inclement.  They are extremophiles, life forms like bacteria, algae and small critters that can endure extremes of temperature, pressure (e.g. deep sea black smokers), radioactivity, darkness, low levels of oxygen, high acidity or alkalinity, and even lack of water. The variety of extreme environments in which these life forms have evolved is, from a scientific perspective, quite stunning in that it provides us with many different analogues for our quest to understand the origin of life on earth, and whether life can exist on other planets.  A few examples are noted below.

 

Nature’s deep-freeze; nature’s caldron

Lake Untersee, in East Antarctic, is up to 160m deep, has a perennially frozen ice cover several metres thick and beneath the ice, clear water with a pH of 10.4 and constant temperature of 4-5oC.  Modern stromatolites are growing, quite happily, on the lake bottom; these are laminated or algal mat-like structures that in this case are composed of cyanobacteria, the same kind of bacteria that flourished during the first 3 billion years of earth history.

Extreme polar deserts in the McMurdo region of Antarctica, the Dry Valleys, also are home to a variety of algae, cyanobacteria, mosses, lichens and a few microscopic invertebrates such as nematodes.  Creature comforts here include average annual temperatures ranging from -14o to -30oC (summer temperatures hover around zero), annual precipitation less than 100mm very little of which is liquid water, and katabatic winds up to 200km/hour (katabatic winds are high density air flows that move downslope under the influence of gravity).  The dry valleys have been used by NASA as testing grounds for Martian exploration.

 

The Andean mountains east of Atacama desert (northern Chile), include some of the driest places on earth.  Salars (salt lakes) here support diverse microbes, green algae, and small crustaceans like brine shrimp in its salars.  Unlike the Antarctic lakes, the Atacama salars, particularly those in the high mountains, have a thick crust of gypsum and halite that cover waters that are 5-10 times more saline than seawater.  Temperature extremes for the mountain salars range from about +20oC to -20oC.  This is also where Flamingos congregate to breed every summer – a spectacular sight.

At the opposite end of the temperature scale are the boiling geothermal hot pools, geysers, and mud pools.  In New Zealand, these silica-rich waters are heated by magma chambers only a few kilometres beneath the surface (this is the Taupo Volcanic Zone).  Specialized microbes are known to form at boiling temperatures (100-105oC) and are also quite prolific in waters 60-80oC.  The biota at the highest temperatures tend to be a bit sparse (I guess there are not many who really want to live there), but they can be detected from organic biomarker molecules and some of the microscopic silica structures that precipitate from hot water.  The siliceous rock that forms in these extreme environments is called geyserite (note that deposits from hot carbonate-rich waters are called travertine, a particular kind of limestone).  Professor Kathy Campbell (Auckland University) and her colleagues have written an excellent technical review of Geyserite (world-wide).  Their studies have also used DNA sequencing to identify and classify the different microbes.

 

Life in the distant past; life on distant planets

Questions about the beginnings of life and whether life exists anywhere else in the universe, invite all manner of responses; wonder, mystery, how, when, and from some, ridicule.  From a scientific perspective, we search for answers in many ways.  Extremophiles have assumed some importance in this regard.

Science’s fascination with extremophiles has several threads.  The metabolism of these sporty life forms provides information on how they thrive, for example in deep-freeze (they produce their own antifreeze proteins), or oxygen-deficient conditions where they derive their metabolic energy from dissolved sulphur (sulphates) and iron compounds.  Studies of extremophile enzymes are already providing technological dividends (making biofuels, gobbling up toxic mining or radioactive waste), and medical research that makes use of extremophile antibiotic, antiviral and antitumor properties.

Life beyond the extremes of our own existence on earth may provide clues to its beginnings long ago.  We have successfully identified primitive forms of bacteria as far back as 3.4 billion years.  Given that the earth is about 4.6 billion years old, and that water had accumulated perhaps 300-400 million years later, it is conceivable that life forming processes were active during these very early times.  The environmental conditions then were extreme.  There was no oxygen, and therefore no protective ozone layer – UV radiation was extreme.  Surface temperatures were probably higher; water vapour and carbon dioxide in the ancient atmosphere probably provided significant greenhouse conditions. The mere existence of extremophiles today tells us that the most primitive life forms could have utilized the extreme conditions during the earliest part of earth history.

The possible development of primitive life forms elsewhere in our solar system is not a huge step in logic, although empirical verification is a pretty big hurdle.  Mars, the nearest and obvious choice for a first look, does have some of the ingredients that we think are essential for life; it has an atmosphere with carbon dioxide, albeit at much lower pressures than earth, it shows clear evidence for water in its distant past, such as river valley landscapes and minerals like calcium sulphate.  It is cold, averaging about -53oC at the surface but not so cold to exclude extremophiles.

There is even conjecture that Europa, one of Jupiter’s small moons (but not much smaller than earth), could harbor if not life forms, then some of the molecular ingredients that might lead to primitive life forms. Europa is thought to be an ice-covered moon with liquid water beneath.  The surface ice is contorted by Jupiter’s massive gravity field, resulting in the large cracks seen in the NASA Galileo mission image.  There is also some evidence for massive water plumes extending geyser-like into space.  At the equator, the temperature is about -160oC; at the poles -220oC, far too cold for even the most extreme extremophiles.  However, gravitational friction may keep the inner part of Europa’s oceans liquid in which case temperatures may by more conducive to life-forming processes.

 

Postscript

Some of these conjectures may seem a bit far-fetched.  But it really wasn’t so long ago that people believed the earth to be 6000 years old (the famous Bishop Ussher calculation – some still do believe this), or that bacteria could not survive, let alone proliferate, in boiling water.  In science, the absurd frequently turns out to be real.

A technical overview of extremophiles (PDF) can be downloaded here

 

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