Monthly Archives: March 2017

Ediacara; Welcome to the revolutionary world of animals

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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

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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. Continue reading

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Sand dunes but no beach; a Martian breeze

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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. Continue reading

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

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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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Striped oceans and drifting continents

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German meteorologist Alfred Wegener, in a fit of creativity, presented his ideas about drifting continents to a 1912 geological meeting in Frankfurt.  He published an expanded version of his theory in 1915 – The Origin of the Continents and Oceans, to muted applause and resounding derision.  I found this quote by Russian contemporary, Vladimir Beloussov, in Arthur Holmes Principles of Geology wherein Beloussov quips in less than glowing terms of the …total vacuousness and sterility of the hypothesis.  The tenor of this remark was probably typical of Wegener’s detractors.  In fact, even today, certain scientific hypotheses and theories suffer the slings and arrows of equally vacuous remarks from the scientifically challenged.  As it turned out, Wegener’s revolutionary ideas were the vital spark that gave birth to modern Plate Tectonics. Continue reading

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