Although it did not appear to hit the popular media, a recent paper on the Earth's earliest non-marine eukaryotes is worthy of note here. Like many discoveries, the researchers were not expecting to find what they did. Conventional wisdom is that the Precambrian land surface was barren, and that the important developments were to be found in the sea. So Torridonian rocks from NW Scotland, having all the marks of non-marine sediments, were not expected to yield much of interest. The story is continued by Cristina Luiggi in The Scientist:
"In 2007, Strother and a colleague came across a dusty museum collection of microfossil slides recovered from an outcrop of the oldest sedimentary rocks in the British Isles: the Torridonian sequence. Sections of these rocks date between 1 to 1.2 billion years, and have preserved sediments that were once part of freshwater lakes formed in the depressions of an ancient land surface. To Strother's amazement, the collection contained what appeared to be fossils of multicellular organisms. "We were finding clusters of cells as well things that looked like little pieces of tissue," he said. This came as a surprise given that multicellular organisms of that time period were believed to exclusively inhabit the oceans."
Artist reconstruction of specimens from the Applecross Formation, Loch Diabaig. (Credit: Oxford University/Martin Brasier, source here)
The find triggered an extensive search using samples gathered from all groups of strata comprising the Torridonian - and evidences of eukaryotes were found at all horizons. This means that from the beginning of the Neoproterozoic era, non-marine eukaryotes have been preserved. The researchers have found complexity, as is shown by the following quote from their paper:
"The Torridonian assemblages contain some striking examples of microfossils that show complexity that goes considerably beyond that of simple leiospheres. Figure 1h illustrates a multicellular sphere from a phosphatic nodule with a clearly differentiated outer wall [. . .] Some of these interior cells retain a dense 'spot', probably the plasmolysed remnants of original cell contents. Figure 2b illustrates a large fusiform vesicle (475 mm wide) with a pitted interior wall structure. Figure 2d shows a dark, heterogeneous central body enclosed within a large cyst with a peripheral asymmetrical structure, which itself appears to consist of several cylindrical cells or membranous outgrowths of the vesicle wall."
They were also impressed by the diversity of what they have documented (possibly 50 species):
"Sample to sample heterogeneity seen throughout the Torridonian clearly indicates a significant degree of biotic diversity, reflecting adaptation to freshwater aquatic and subaerially exposed habitats by earliest Neoproterozoic time. Early eukaryotes were clearly capable of diversifying within non-marine habitats, not just in marine settings as has been generally assumed."
What do these findings mean for our understanding of life on the Precambrian Earth? Dr Charles Wellman, an author of the paper, is quoted by ScienceDaily as saying:
"It is generally considered that life originated in the ocean and that the important developments in the early evolution of life took place in the marine environment: the origin of prokaryotes, eukaryotes, sex and multicellularity. During this time the continents are often considered to have been essentially barren of life -- or at the most with an insignificant microbial biota dominated by cyanobacteria. We have discovered evidence for complex life on land from 1 billion year old deposits from Scotland. This suggests that life on land at this time was more abundant and complex than anticipated. It also opens the intriguing possibility that some of the major events in the early history of life may have taken place on land and not entirely within the marine realm."
We should note that marine organisms are isotonic with seawater: this means the same salt concentration exists inside as well as outside the cell membrane and there are no osmotic pressures. However, fresh-water and land organisms are all hypertonic, which means that the internal salinity exceeds that of the fresh-water outside the cell, and unless there are mechanisms to counter osmosis, the cell will die. In addition, non-marine life may have to face the problem of desiccation. This appears to be a real issue for some of the Torridonian eukaryotes, because some of the samples were obtained from desiccation cracks in the Diabaig Formation at Loch Diabaig (this is of personal interest, having obtained samples of these desiccation cracks some years ago from this same locality). The researchers comment:
"Freshwater habitats are ecologically more variable than marine habitats, providing temporal and physiochemical heterogeneity, including wet-drying cycles and direct atmosphere-organism gas exchange. Such habitat heterogeneity translates directly into increased speciation potential. Some of the microfossils illustrated here must have experienced subaerial exposure because they occur in situ in microbially induced sedimentary structures with desiccation cracks, but the extent to which they lived subaerially cannot be ascertained with certainty."
Speciation potential is fair enough as a concept, but the hard work then starts - to identify viable routes for generating the relevant biological mechanisms and associated information. This is where big questions have to be raised about the viability of mutation and natural selection to deliver significant changes (see here). When confronted by the realities of the changes that are needed, it is very easy for evolutionists to put out what they call a plausible narrative - otherwise known as "Darwinian storytelling".
One of the themes developed in this blog has been an ecological perspective on the fossil record. This suggests that the key issues to grasp when seeking to understand past life relate to ecology and the environment. Here we have another example. In the Neoproterozoic, seawaters were not yet able to support multicellular animals - for these, the Earth had to wait until the Ediacaran (for an advance party) and then the Cambrian (for the explosion of animal life).
Nevertheless, the Neoproterozoic could support some eukaryote species (as well as prokaryotes). And that's what we find, not only in the seas but also on land. The word "surprising" appears alongside this discovery, but this draws its rationale from Darwinian gradualism - but from a design perspective, the Earth was ready for freshwater life.
"We've been thinking about the evolution of life in the Precambrian as primarily happening in the oceans," Strother said, "but 1 billion years ago, fresh water environments were really teeming with life."
The existence of a terrestrial Precambrian (more than 542 Myr ago) biota has been largely inferred from indirect chemical and geological evidence associated with palaeosols, the weathering of clay minerals and microbially induced sedimentary structures in siliciclastic sediments. Direct evidence of fossils within rocks of non-marine origin in the Precambrian is exceedingly rare. The most widely cited example comprises a single report of morphologically simple mineralized tubes and spheres interpreted as cyanobacteria, obtained from 1,200-Myr-old palaeokarst in Arizona. Organic-walled microfossils were first described from the non-marine Torridonian (1.2-1.0 Gyr ago) sequence of northwest Scotland in 1907. Subsequent studies found few distinctive taxa - a century later, the Torridonian microflora is still being characterized as primarily nondescript "leiospheres". We have comprehensively sampled grey shales and phosphatic nodules throughout the Torridonian sequence. Here we report the recovery of large populations of diverse organic-walled microfossils extracted by acid maceration, complemented by studies using thin sections of phosphatic nodules that yield exceptionally detailed three-dimensional preservation. These assemblages contain multicellular structures, complex-walled cysts, asymmetric organic structures, and dorsiventral, compressed organic thalli, some approaching one millimetre in diameter. They offer direct evidence of eukaryotes living in freshwater aquatic and subaerially exposed habitats during the Proterozoic era. The apparent dominance of eukaryotes in non-marine settings by 1 Gyr ago indicates that eukaryotic evolution on land may have commenced far earlier than previously thought.
Supplementary information here.
Loch Fossils Show Life Harnessed Sun and Sex Early on, ScienceDaily (14 April 2011)
Luiggi, C. Old open air voyagers, The Scientist (13th April 2011)
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