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Sea-faring creatures from ages ago just won't go away. New data from the fossil record concerning a dramatic "explosion" of life forms about 543 million years ago continue to baffle evolutionary scientists. A few years ago one biologist wrote, "Elucidating the materialistic basis of the Cambrian explosion has become more elusive, not less, the more we know about the event itself."1 Indeed, since 2009 the "materialistic basis" itself has become dramatically less tenable. What follows is a brief description of what we know of the first appearance of animals on Earth that includes some of the latest scientific findings. Do these findings support an entirely natural first appearance of such complex creatures, or does supernaturalism best explain the evidence?
First, let's back up a few tens of millions of years. Until 575 million years ago, prokaryotes—unicellular organisms that lack a membrane-bound nucleus—were dominant among Earth's life forms. While a few more complex organisms called eukaryotes also existed, they were confined to shallow-water environments, and their body sizes remained microscopic.
This is not surprising, given the conditions on Earth at the time. Not until after the Gaskiers glaciation event occurred, some 580 million years ago, did bottom ocean waters transition from being anoxic, that is, oxygen-starved, to oxic, having oxygen present. Surface ocean waters also transitioned from only having pockets of oxic conditions to being ubiquitously oxygen-rich.
The surprise comes from discovering how, immediately after this oxygen enrichment event occurred, large, architecturally complex organisms appeared. As soon as oxygen reached the minimum level for the survival of these organisms, they were here, with little or no measurable delay. Evidence shows sudden rather than gradual change in body size, systemic sophistication, and morphological complexity.
First Avalon Explosion
The first large-bodied animals appeared in Newfoundland's Avalon Peninsula 575 million years ago. The body size and morphological complexity of these creatures took maximal and immediate advantage of the oxygen levels, food supplies, and nutrients newly available after the Gaskiers glaciation event. Overall, the Avalon explosion constituted a huge upsurge in Earth's biomass and biodiversity.
A defining feature of Avalon animals is their very large surface area to volume ratios. The many sponge species that arose greatly enhanced the living space over which photosynthetic bacteria and algae could thrive. In return, the bacteria and algae living on and within the bodies of these Avalon animals supplied them with abundant photosynthetic products. The symbiotic relationships that developed demonstrate how the introduction of new species, rather than replacing former species or greatly diminishing their numbers, can actually increase their populations and make possible a diversification of their kinds.
Second Avalon Explosion
Although Avalon animals were large, they lacked eyes, ears, mouth, digestive tract, and anus. These early filter-feeding organisms lived predominantly on seafloors. Their fossils show no evidence that they possessed mobility. Most were permanently attached to the sea bottom by holdfast structures. The existence of more complex animals required the presence of more oxygen.
As soon as oxygen levels in shallow marine environments stabilized, 560 million years ago, creatures with a limited capacity for movement or burrowing appeared, and there is some evidence that in one case they also featured bilateral-like symmetry in their body structure.2 Ten million years later (550 million years ago), thinly calcified tubular and goblet-shaped organisms arose by taking immediate advantage of a mineral infusion. However, as with the first Avalon explosion, none of these animals yet possessed eyes, ears, or a digestive tract.
Then, between 544 and 543 million years ago, Avalon explosion animals suffered a mass extinction event. So catastrophic was this extinction that the number of Avalon species that survived into the subsequent era "can be counted on the fingers of one hand."3 A short-lived global anoxia event (oxygen loss) offers the most probable explanation for this mass extinction.
Less than a million years (geologically, a mere blink of an eye) following the mass extinction of the Avalon biota, the first animals manifesting bilateral symmetry and hard body parts appeared. These first skeletal animals arrived not in just one or two phyla (basic body plans). Fossils unearthed in southern China and in the Canadian Rockies reveal that 50–80 percent of all the animal phyla known to have existed at any time in Earth's history appeared within no more than a few million years of one another, as the Cambrian era began, 542–543 million years ago.
The sudden appearance of these new life forms, called the Cambrian explosion, featured a vast array of creatures, including ones with every kind of skeleton known to have existed, past or present:
• internal and external
• rigid and flexible
• rod-based, plate-based, and combinations of rods and plates
• calcium carbonate, calcium phosphate, chitin, or silica
• fixed, molting, or remodeling
A total of 182 animal skeletal designs are theoretically permitted by the laws of physics. Geologists at Franklin and Marshall College have shown that at least 146 different designs appear among the fossils of the Burgess Shale formation in the Canadian Rockies.4 Given the ecological and habitat constraints existent at the time, this number of skeletal plans—
80 percent of all physically conceivable designs—stirs a sense of amazement and wonder.
Until the Cambrian period, sea chemistry did not permit the formation of skeletons. The Cambrian explosion of animal phyla occurred just as the oceans and seas for the first time attained, via a protected and widespread continental erosion episode called the Great Unconformity, high abundances of phosphorus, magnesium calcite, silica, and aragonite (calcium carbonate). This chemical change in seawater occurred on a global scale, and so did the proliferation of Cambrian biota.
When first confronted with fossil evidence for the Cambrian explosion, most paleontologists presumed that the event involved invertebrate creatures only. Vertebrates (animals possessing a backbone) were thought to have arrived much later. But this perspective changed when a team of Chinese and British geologists discovered fossils of jawless vertebrates in the early Cambrian fossil beds at Chengjiang, in southern China. The discovery of similar fish in the Burgess Shale of British Columbia revealed that these creatures must have been widespread. These finds pushed back the date for the appearance of the first fish by nearly 70 million years.
The Chengjiang fossil beds also yielded important members of the most complex phylum, the chordata, to which humans belong. One well-preserved fossil exhibited "a heart, ventral and dorsal aorta, an anterior branchial arterial, gill filaments, a caudal projection, a neural cord with a relatively large brain, a head with possible lateral eyes, and a ventrally situated buccal cavity with short tentacles."5 An international research team found fossils of shrimp-like creatures that possessed a brain and optic neural lobes, as well as a heart and a fully developed cardiovascular system. In the words of one research team, "the co-occurrence of stem-group deuterostomes and agnathan fish are consistent with an 'explosion' of metazoan body plans in the latest Neoproterozoic and early Cambrian."6
The first optical devices in animals also appeared during the Cambrian explosion. These first eyes included reflectors, lenses, and corneas. Nearly every eye design that exists today has been found in Cambrian organisms—compound eyes with numerous hexagonal facets, freely movable eyes on top of both short and long stalks, and inset eyes. These multiple eye designs all appeared in the fossil record at the same time.
More Evolutionary Surprises
The Cambrian period features the simultaneous occurrence of animals that flourish in the open ocean and animals that dwell on the ocean bottom. Evolutionary models had predicted that the bottom dwellers would appear long before the open-ocean swimmers, since the latter need appropriate biomechanics for buoyancy, locomotion, and the exploitation of open-water nutrients. Yet both bottom and open-ocean animals appeared early and simultaneously.
The discovery of optimized ecological relationships also surprised researchers. Instead of there being a slow, gradual development of predator-prey relationships, these relationships appeared at the outset of the period. Paleontologist Simon Conway Morris commented that the Cambrian fauna attained this optimization without any measurable delay.7
Numerous books and research papers convey scientists' profound amazement about the Cambrian fossils. Here are a few of their comments:
The Cambrian strata of rocks, vintage about 600 million years, are the oldest ones in which we find most of the major invertebrate groups. And we find many of them already in an advanced state of evolution, the very first time they appear. It is as though they were just planted there, without any evolutionary history.8
—Richard Dawkins (evolutionary biologist)
No single environmental or biological explanation for the Cambrian explosion satisfactorily explains the apparent sudden appearance of much of the diversity of bilaterian animal life.9
—Jeffrey Levinton (marine ecologist, evolutionary biologist)
The Cambrian "explosion" of body plans is perhaps the single most striking feature of the metazoan fossil record. The rapidity with which phyla and classes appeared during the early Paleozoic, coupled with much lower rates of appearance for higher taxa since, poses an outstanding problem for macroevolution.10—Gregory Wray (evolutionary biologist)
Paleontologists and evolutionary biologists seeking a naturalistic explanation for the Cambrian explosion have proposed that the proliferation of extreme genetic diversity came about through multiple mutation events from a common ancestor. Estimates of the genetic diversity and mutation rates of Cambrian animals were formulated, derived in part from known genetic diversity and mutation rates of currently existing species that share similar body structures, sizes, functions, and feeding habits. Evolutionary biologists then used these estimates to calculate when, at the latest, the presumed common ancestor may have existed. The best such calculation yields a date between 777 and 851 million years ago.11 Even if they apply extremely high and admittedly unreasonable mutation rates, they still came up with a divergence date (from one or more common ancestors) no farther back than 586 million years ago.
The fossil data, as we have seen, contradicts these molecular clock dates. Fossil evidence indicates that the great radiation (the first appearance and diversification) of Cambrian fauna occurred sometime after 542 million years ago. The physical and chemical conditions on Earth between 586 and 851 million years ago—that is, before the Gaskiers glaciation event—also present an intractable problem. The lack of oxygen and mineral nutrients during that epoch rule out the survivability of any conceivable common ancestor. And there are other problems surrounding naturalistic explanations for the Cambrian explosion.12 Evolutionary biologist Thomas Cavalier-Smith has concluded, "Evolution is not evenly paced and there are no real molecular clocks."13
The Avalon and Cambrian explosions profoundly challenge naturalistic explanations for life's history, but they also point to something more. They demonstrate how the just-right introduction and removal of certain life forms at the just-right times in the just-right places left a build-up of vast stores of biodeposits (for example, limestone and fossil fuels) that have enabled the launch and maintenance of human civilization. Each of these stepwise, beneficial changes signals the activity of a supernatural, loving, super-intelligent agent. •
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