Fossils and the Cambrian Explosion
A Graphical Overview
The following review, graphics, and terms are offered to illustrate the far reaching implications of the fossil evidence especially from the Cambrian Era.
The initial diagrams are similar to those that appear in a number of publications. For example, we recommend a reading of the 'Excursion Chapter 4, The Fossil Record' that appears in the book Of Pandas and People The Central Question of Biological Origins. This text is designed to serve as a companion text to standard biology textbooks. As such, this companion is a source of valuable insights that are often not presented in the public classroom setting. This overview is also updated with points illustrated by Meyer, et al., in their book chapter entitled The Cambrian Explosion: Biology's Big Bang (see reference).
The initial diagrams are offered to illustrate commonly accepted classical views. By the time you reach the end of this page these views will be left unsupported by the actual physical fossil evidence.
The Darwinian concept pictures development of life forms as a source of diversity through evolution. This is the typical 'tree of evolution' [also see feature article on the 'tree of life'] that many of us are familiar with from common textbook presentations.
This illustration simply indicates, that over time the information within the ancestral life forms in some way changes. This 'splits out' or produces new life forms to create the branching appearance in the diagram above. The branching depends on transitions and thus one would expect to see transitional forms of life leading to the refined forms of life further out on a branch. The implication is that all life is traceable to several or a single ancestor form. In the most extreme sense, one might suggest all life started with a simple single cell organism. Darwin would say, by natural selection, chance, and time, that the simple form gave rise to increasingly more complex and more diverse forms.
The key point to keep in mind here is that the major groups of life forms, the phyla, in this example, if true, all have a common root at the base of the tree. This is the gradualist view, that is to say, there must be sufficient time to allow for all the developments to occur and thus allowing the tree to branch out as depicted here.
Punctuated Evolution Is This It?
The suggestion that new forms appear rapidly in the fossil record prompted Gould and Eldridge to propose the concept of 'punctuation' whereby rapid genetic shifts are presumed to give rise to new life forms. The nature of the links depicted here as dotted lines is based on uncertainty and no evidence.
Another way of looking at this tree comes by projecting the end points of the tree's branches onto a surface as is done at the top of the diagram above. This separates presumed related groups into separate groups without forcing the notion of linkage throughout all types. So, did phyla appear already formed and separate or did virtually instantaneous jumps occur?
What Does the Fossil Record Actually Show?
A generalized schematic of the fossil record shows that there is evidence for the presence of life forms that appear at various times, but most surprisingly there is a lack of complex (animal) forms prior to the Cambrian era. At points in time when new organisms appear in the fossil record, they appear complete and not as some intermediate form [a similar but less widely heralded sudden appearance occurs later for flowering plants]. But unlike the tree diagram above, the main body plans of animal life all appear in a relatively short period of time as illustrated in the next diagram [again, this leads to considering a hierarchical or polyphyletic origin].
A diagrammatic representation of Cambrian origins of fossil groups and those groups that still exist to present time appears below.
So, where is the explosion? Well, right there at that line between Precambrian and Cambrian. This is a point about 530 million years ago (MYA). Some previous estimates suggest the major groups of animals all appeared within a time span of say 10 to 50 million years, later the number dropped to 10 million, but more recent work suggests the window of time is even narrower and is 5 or so million years. In terms of geologic time this is an appearance in an instant. For this reason, the event is also been dubbed 'biology's big bang.'
There was life on Earth prior to 530 MYA, but the forms were much simpler. There was a fossil record before the Cambrian burst of life! It just does not contain the complex and diverse life forms that appear with the explosion. What must be remembered is that features like eyes, organs, and simply those irreducibly complex cellular systems (structures and metabolism) appear within this early Cambrian event. In other words, this certainly brings to mind terms like creation event as opposed to evolutionary era.
Recent science exploration in China also shows remarkable preservation of sponge embryos (microfossils preserving cellular detail) in the geological horizon just below the Cambrian fossil beds. This strongly refutes any notion that conditions prior to the Cambrian were not adequate to preserve fossils.
The Fossil Record at Face Value
... this is essentially the picture that one sees from the field evidence!
Please note we understand the diagrams are simple and the array of life forms is marvelously complex and varied. That however only lends greater support to the point of this overview.
At this point you you have learned enough to explore further and to do this we suggest reading other publications. The following list of sources add various levels of detail to the discussion presented above, but all will provide greater depth than what is offered here. Our purpose is to first make the simple but significant point that even the fossil record does not the support the Darwinian view ... and frankly nothing here opposes the basic description of origins as outlined in the brief account of Genesis.
Bottom-Up or Top-Down Evolution?
A bottom-up pattern fits the Darwinian view as illustrated above. The following diagram represents the top-down concept. As sudden appearances indicate, unique phyla appear first and only later do we see classes, genera, etc. We end up with fossils telling us the opposite of what the Darwinian view has projected for over 150 years. Evolution is flipped and its fossil evidence that does it.
What The Cambrian Fossils Reveal:
The following quote from Dr. Robert DeHaan helps to characterize what we are seeing here (quote from Do Phyletic Lineages Evolve from the Bottom Up or Develop from the Top Down? Perspectives on Science and Christian Faith Vol 50, Number 4, December 1998):
'The Cambrian animals were the ancient founding parents of all but one (Bryozoa) of the major groupings of animals, 37 of which have survived to the present time. This then is where the top-down direction of change had its origin.
'Each of the fifty animals possessed its own unique structural architecture or body plan, which became the identifying characteristic of the phylum they founded. They bequeathed this body plan on all their progeny. Even today it shows up in the embryonic stage of every one of their offspring and is the distinguishing mark of each phylum.
'In sum, four characteristics mark the Cambrian explosion from all other events in history of life: (1) its amazing speed (five million years), (2) its incredible breadth (fifty disparate, unique animals), (3) its finality (only one additional phylum formed after this time, and (4) its significance (it is the point of origin of virtually all animal phyla).'
So, of the original 50 body plans, 37 remain today. With one exception there is no evidence for the appearance of any others after the Cambrian event. In fact, the record lacks evidence for evolution of unique groups. From the unique phyla at their start is the source material from which species arise. DeHaan is saying phyla first species later ... instead of the other way around as would be suggested by Darwin.
DeHaan follows with an account of fossil evidence that does in fact occur just before the time of the Cambrian explosion. Thus, the burst of life forms is simply not an artifact of a void in fossil preservation prior to the main event. Fossil preservations are contiguous from before the event itself.
Summary Points That Fit the Current Fossil Data:
The following is summarized from the article by Meyer and coauthors:
NOTE: This section is currently being drafted and will be updated very soon!
1 - Geologic Sudden Appearance
2 - Morphology (form) of Fossils is Initially Diverse (Broad)
3 - Morphology (forms) Are Isolated (Persistent Disparity)
4 - Sudden Appearance Brings a Huge Increase in Information 'All At Once'
5 - The Data as Such Offer an Alternative View Concerning Life's Appearance
Publications for further reading:
Of Pandas and People The Central Question of Biological Origins.
The book chapter: The Cambrian Explosion: Biology's Big Bang, by Meyer, Ross, Nelson and Chein appears in Darwinism, Design, and Public Education.
Not referenced above, but containing relevant comments concerning fossils: Evolution: A Theory in Crisis. 1985. by M. Denton.
See our entire booklist.
A Few Definitions:
At the end of this section we provide references for readings that provide additional information on this topic. The following defines several terms to help in understanding the text and graphics presented above.
Cambrian Era: ... previously called the Silurian, the geologic time, system of rocks, and sedimentary deposits of the first period of the Paleozoic Era, characterized by warm seas and desert land areas.
Fossil: A remnant or trace (2 or 3 dimensional impression or representation) of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded and preserved in the earth's crust.
Gradualism: The view that evolution occurred gradually over time, with transitional forms grading finely in a line of descent. [see first illustration above; descent in this case would be from a single ancestor from the bottom up to the present day more complex life forms]
Phylum (pl. Phyla): A standard dictionary definition would read: ''A primary division of a kingdom, as of the animal kingdom, ranking next above a class in size.''
This term is used here to indicate 'groups of organisms' (e.g., a distinct group of animals relative to other animals) as differentiated by distinct 'body plans.' For example, body plans include soft bodied worms as opposed to another group with a body plan inclusive of a backbone. In this way phyla means distinct groups [with no immediate or apparent relation to other phyla]. This is the way Linneaus used the term when he classified organisms.
Species: a. A fundamental category of taxonomic classification, ranking below a genus or subgenus and consisting of related organisms capable of interbreeding. b. An organism belonging to such a category, represented in binomial nomenclature by an uncapitalized Latin adjective or noun following a capitalized genus name, as in Ananas comosus, the pineapple, and Equus caballus, the horse.
Speciation: The development of a new species by reproductive isolation from their ancestral population, resulting inn the loss of interfertility with the ancestral group.
Punctuated equilibrium: The theory that speciation occurs relatively quickly, when spurts of rapid genetic change ''punctuate'' the ''equilibrium'' of primarily constant morphology known as stasis over geologic time.
References of Interest