Common Design vs. Common Descent

I promised John Harshman for several months that I would start a discussion about common design vs. common descent, and I’d like to keep my word to him as best as possible.

Strictly the speaking common design and common descent aren’t mutually exclusive, but if one invokes the possibility of recent special creation of all life, the two being mutually exclusive would be inevitable.

If one believes in a young fossil record (YFR) and thus likely believes life is young and therefore recently created, then one is a Young Life Creationist (YLC). YEC (young earth creationists) are automatically YLCs but there are a few YLCs who believe the Earth is old. So evidence in favor of YFR is evidence in favor of common design over common descent.

One can assume for the sake of argument the mainstream geological timelines of billions of years on planet Earth. If that is the case, special creation would have to happen likely in a progressive manner. I believe Stephen Meyer and many of the original ID proponents like Walter Bradley were progressive creationists.

Since I think there is promising evidence for YFR, I don’t think too much about common design vs. common descent. If the Earth is old, but the fossil record is young, as far as I’m concerned the nested hierarchical patterns of similarity are due to common design.

That said, for the sake of this discussion I will assume the fossil record is old. But even under that assumption, I don’t see how phylogenetics solves the problem of orphan features found distributed in the nested hierarchical patterns of similarity. I should point out, there is an important distinction between taxonomic nested hierarchies and phylogenetic nested hierarchies. The nested hierarchies I refer to are taxonomic, not phylogenetic. Phylogeneticsits insist the phylogenetic trees are good explanations for the taxonomic “trees”, but it doesn’t look that way to me at all. I find it revolting to think giraffes, apes, birds and turtles are under the Sarcopterygii clade (which looks more like a coelacanth).

Phylogeny is a nice superficial explanation for the pattern of taxonomic nested hierarchy in sets of proteins, DNA, whatever so long as a feature is actually shared among the creatures. That all breaks down however when we have orphan features that are not shared by sets of creatures.

The orphan features most evident to me are those associated with Eukaryotes. Phylogeny doesn’t do a good job of accounting for those. In fact, to assume common ancestry in that case, “poof” or some unknown mechanism is indicated. If the mechanism is unknown, then why claim universal common ancestry is a fact? Wouldn’t “we don’t know for sure, but we believe” be a more accurate statement of the state of affairs rather than saying “universal common ancestry is fact.”

So whenever orphan features sort of poof into existence, that suggests to me the patterns of nested hierarchy are explained better by common design. In fact there are lots of orphan features that define major groups of creatures. Off the top of my head, eukaryotes are divided into unicellular and multicellular creatures. There are vetebrates and a variety of invertebrates. Mammals have the orphan feature of mammary glands. The list could go on and on for orphan features and the groups they define. Now I use the phrase “orphan features” because I’m not comfortable using formal terms like autapomorphy or whatever. I actually don’t know what would be a good phrase.

So whenever I see an orphan feature that isn’t readily evolvable (like say a nervous system), I presume God did it, and therefore the similarities among creatures that have different orphan features is a the result of miraculous common design not ordinary common descent.

3,738 thoughts on “Common Design vs. Common Descent

  1. Mung,
    And I guess discussion regarding the age of fossils that is derived from the age of surrounding rock will be pointless if Bill is wedded to YEC beliefs that the Earth is only 6,000 years old.

    Just as discussion regarding evolutionary biology is pointless with Sal when he clings to the same belief.

    ETA or, maybe more bizarre, old Earth with life that was seeded 6,000 years ago. How did young fossils get in old rocks?

  2. Allan Miller: We can see this focus in the repeated refusal to even look at the molecular evidence. Again and again, we get a brief blink, then a hurried ‘let’s-talk-about-something-else’. Trilobite eyes is but the latest.

    That’s a bit optimistic. 🙂 As in ‘look at that squirrel”. I don’t expect Bill to be any more interested in discussing trilobites and whether their visual adaptations fit neatly into a nested hierarchy than in molecular phylogenies. Would it be any more focused with separate threads? Not sure I have time or the qualifications for more than a “Wow aren’t trilobites cool but watch out for Moroccans” thread.

  3. keiths: . I also can’t see any benefit of erasing the distinction and classifying HGT as a form of “common descent”.

    It’s not really much different from mutations, which begin as breaks from common descent. It’s like HGT is a kind of mutation, it appears as something different from common descent, but it becomes part of common descent if it manages to propagate throughout a species.

    Mutations, HGT, or both, can provide the changes that cause the branching of the clades.

    Glen Davidson

  4. Alan Fox: Just as discussion regarding evolutionary biology is pointless with Sal when he clings to the same belief.

    ETA or, maybe more bizarre, old Earth with life that was seeded 6,000 years ago. How did young fossils get in old rocks?

    How did evolutionary patterns get into designed organisms?

    I don’t know which is more bizarre, actually. The answer, though, is “not evolution.” Beyond that he doesn’t seem to bother.

    Glen Davidson

  5. Allan Miller: We can see this focus in the repeated refusal to even look at the molecular evidence. Again and again, we get a brief blink, then a hurried ‘let’s-talk-about-something-else’. Trilobite eyes is but the latest.

    I’m sure he’d be willing to talk abut the DNA sequences for trilobite eyes.

  6. Alan Fox,

    I would be interested in how you would explain trilobites in terms of a nested hierarchy and how you would use data to determine the pattern. If you could include the eye in the discussion even better.

  7. Alan Fox,

    And I guess discussion regarding the age of fossils that is derived from the age of surrounding rock will be pointless if Bill is wedded to YEC beliefs that the Earth is only 6,000 years old.

    From now on we can go with the 4.5 billion year earth unless you object 🙂

  8. colewd,

    Just trying to see where you’re coming from. Some creationists say there is no nested hierarchy and other say there is.

    The problem is there are two kinds of nested hierarchies, one that is taxonomic (real) and one that is phylogenetic (imaginary).

    Do you agree the taxanomic nested hierarchy is real? A simple example:

    Angio Sperms (flowering plants) nest within Vascular Plants, which nest within Multicellular creatures, which nest within Eukaryotes.

    Does that agree with what you see?

  9. Glen,

    It’s not really much different from mutations, which begin as breaks from common descent. It’s like HGT is a kind of mutation, it appears as something different from common descent, but it becomes part of common descent if it manages to propagate throughout a species.

    Mutations, HGT, or both, can provide the changes that cause the branching of the clades.

    I made the same point here:

    But again, what creates the strong phylogenetic signal is (imperfect) vertical inheritance. The HGT event creates a marker in the recipient, but it is the subsequent branching descent of that marker that reinforces the objective nested hierarchy.

    This makes sense. We’re talking about common descent, after all, so it’s no surprise that vertical inheritance establishes the pattern, and that horizontal transfers are noise.

    Allan rejects that and wants the HGT event itself to count as an instance of descent. Hence my objection:

    I also can’t see any benefit of erasing the distinction and classifying HGT as a form of “common descent”.

  10. Allan Miller:

    Yeah, same objections as before, as you continue to bellow sententiously: “AND ANOTHER THING …”. You equate possible constraint on part of a sequence with constraint on all sequence ever. Again. And again. And again.

    No I don’t, but I was pointing out how badly evolutionists need to have absence of functional constraint to make their theory coherent. At best common descent is a rush to judgement, not a real scientific hypothesis like say electromagnetism.

    You keep say X happened, but fail to point out the many areas you haven’t confirmed that could be contrary.

    Maybe 10 years ago few people would have confronted you with the constraints I listed. Arguing protein evolvability centered around Doug Axe type arguments. Now there are more angles than just Axe-like arguments and the trend of discovery is worse for common descent as time passes.

    That’s why now there is a rift between real research outfits like the National Institutes of Health and Evolutionary Biologists like Dan Graur. That rift will continue until Evolutionary Biologists adapt to new data and provide a nnew generation ad hoc, flimsy, and incoherent explanations.

    Allan Miller:

    Yeah, same objections as before, as you continue to bellow sententiously: “AND ANOTHER THING …”. You equate possible constraint on part of a sequence with constraint on all sequence ever. Again. And again. And again.

    I equate possible constraint with common descent being possibly wrong, something you seem insistent can’t be wrong even if you saw God work a miracle of special creation with your own eyes.

    Ok so if God worked a miracle of special creation before you own eyes and he said with a thundering voice from heaven that “Darwin was wrong, special creation was right” would that convince you? Is that about how big a gap you’ll need to reject evolutionary theory? If so, I respect that. Skepticism is a virtue.

    But there’s an old saying in the casino, play the hand you’re dealt. So given the absence of conclusive facts, we just make our best guess. I don’t disrespect your view because of of the absence of facts. I will however disrespect your uncritical acceptance that it’s natural for orphan features to evolve so naturally. I’ve provided numerous mechanistic issues that you just dismiss.

    Maybe you shouldn’t be so insistent with your belief that something is fact until you actually have facts, you should just call them articles of faith.

  11. I repeat:

    Sal,

    Just to keep you on your back foot:

    The elephant is still in the room. Would you care to explain to us why, out of the more than 10^38 possible trees for the taxa in Theobald’s Figure 1, we infer the same exact tree from the morphological and molecular data?

    Coincidence? The Designer just happens to be an anal-retentive evolution mimic? He hates the eggheads and wants to fool them into accepting common descent?

    Be brave and answer the question.

  12. Mung: Simple. Common design.

    Do you mean poof? The scientific explanation for fossils that they are organisms that end up dead in an environment where they are not scavenged or otherwise degraded so enough material (usually hard parts, especially teeth) gets preserved in something like sediment or tar pits or amber which then hardens into rock. The remains also mineralize. So the fossil and the surrounding rock are contemporary.

    Can you expand on the common design explanation? Or did I miss the irony?

  13. colewd:
    Alan Fox,

    I would be interested in how you would explain trilobites in terms of a nested hierarchy and how you would use data to determine the pattern. If you could include the eye in the discussion even better.

    I’m only offering to go through the evidence with you. I’m no expert on the details but I would assume that trilobite fossils are dated from identifying the rock layer in which the fossil is found. I think radiometric dating is also done. I believe trilobite fossils are so widely distributed and particular examples appear in particular layers with enough precision and regularity they can be used as index fossils, as a check on other dating methods. Also other index fossils found in association with trilobites can add to the dating evidence.

    So the first step in arranging trilobites in sequence is to date them. OK so far?

  14. colewd:
    Alan Fox,

    From now on we can go with the 4.5 billion year earth unless you object 🙂

    So, are you accepting that the earliest trilobite fossils date from deep in the Cambrian, maybe 520 million years ago? Earlier fossilised tracks hint at trilobite ancestors without armoured exoskeletons.

  15. colewd: Trilobites have DNA sequences?

    Not any more. In ideal conditions, DNA does not seem to survive long in fossil bones and teeth, perhaps a few hundred thousand years

  16. colewd:
    Alan Fox,

    I would be interested in how you would explain trilobites in terms of a nested hierarchy and how you would use data to determine the pattern.If you could include the eye in the discussion even better.

    I know you don’t read papers that people cite, but this one shows how trilobites fit into the nested hierarchy of life. There are many such papers. This is just the first one I remembered the citation for. The answer to “how you would use data” is “the usual way”. Read any paper in which there’s a phylogenetic analysis of any taxa.

    Lee et al. Rates of Phenotypic and Genomic Evolution during the Cambrian Explosion. 2013. Current Biology 23: R878-R880.

    Oops, no trilobites in that one, just extant arthropods. Still, same methods. Here’s one with trilobites:

    Lieberman BS, Karim TS. Tracing the trilobite tree from the root to the tips: A model marriage of fossils and phylogeny. 2009. Arthropod Structure and Development 39:111-123.

  17. stcordova: The problem is there are two kinds of nested hierarchies, one that is taxonomic (real) and one that is phylogenetic (imaginary).

    No, there are not. The taxonomic nested hierarchy is an attempt to approximate the phylogenetic hierarchy. Phylogeny explains why there is a nested hierarchy at all. You have no explanation for it, and you have consistently ignored all attempts to coax you into producing an explanation, like this attempt, now, which I predict you will ignore.

    Do you agree the taxanomic nested hierarchy is real? A simple example:

    Angio Sperms (flowering plants) nest within Vascular Plants, which nest within Multicellular creatures, which nest within Eukaryotes.

    Does that agree with what you see?

    That’s a really bad example. First, the term is “angiosperms”, one word. Second, “multicellular creatures” is not a taxonomic term or group, and in fact multicellularity arose independently for animals, plants, and several other groups. You show great ignorance of biology every time you type, and those are just another few minor examples of it.

    Incidentally, why is there a nested hierarchy within plants?

  18. John Harshman:

    The taxonomic nested hierarchy is an attempt to approximate the phylogenetic hierarchy.

    Taxonomic hierarchies are real, phylogenetic hierarchies are imaginary. You’re so steeped in your belief system you can’t distinguish empirical facts from your imaginations.

  19. John Harshman: Second, “multicellular creatures” is not a taxonomic term or group, and in fact multicellularity arose independently for animals, plants, and several other groups.

    Very interesting. This made me wonder if there is any multicellular organism known that never goes through a single-celled stage. AFAIK all animals go through a single-celled stage.
    But are there some multicellular organisms that go through a “smaller colony” stage (for lack of knowing a better term) without passing on only a single cell?

  20. Rumraket,

    Photobionts?

    [I was driven to this lame-ass suggestion by my inability to find any beastie that propagates via fragmentation (willow trees? wtf? you learn something new every day!) and has definitively lost the ability to produce spores/seeds…]

  21. stcordova: Taxonomic hierarchies are real, phylogenetic hierarchies are imaginary.

    So you claim, but without any justification. Please explain what you mean and how you know it’s true.

    Rumraket: Very interesting. This made me wonder if there is any multicellular organism known that never goes through a single-celled stage. AFAIK all animals go through a single-celled stage.
    But are there some multicellular organisms that go through a “smaller colony” stage (for lack of knowing a better term) without passing on only a single cell?

    That depends on what you mean by “organism”. Many animals reproduce vegetatively. You’ve probably seen pictures of little hydras growing out of the sides of big hydras. I’d say those little hydras never go through a one-cell stage. And of course lots of plants and fungi do the same thing.

  22. John Harshman: Phylogeny explains why there is a nested hierarchy at all. You have no explanation for it, and you have consistently ignored all attempts to coax you into producing an explanation, like this attempt, now, which I predict you will ignore.

    And my prediction is borne out. OK, it was a pretty safe prediction. I also predict that water will continue to be wet.

  23. John Harshman: I also predict that water will continue to be wet.

    At ENV and at UD they are touting a new book by Michael Denton about all the marvellous properties of water that enable life. Now as far as I know all the properties of water are consequences of the solutions of the Schrödinger Wave Equation. A Designer could not tinker with the properties separately, she would have to tinker with the SWE itself.

    Still, if the Designer is that powerful, she could make unwet water by doing that.

  24. keiths,

    Allan rejects that and wants the HGT event itself to count as an instance of descent. Hence my objection:

    No, you really aren’t getting it. I don’t want HGT to be an ‘instance of descent’. I’ve said this a few times now. HGT is one of the paths by which sequences travel, from their common ancestor (a sequence, not an individual or a species).

  25. stcordova,

    I equate possible constraint with common descent being possibly wrong, something you seem insistent can’t be wrong even if you saw God work a miracle of special creation with your own eyes.

    If I saw someone magic up a species, it would not prove that all species were magicked up. And I would still wish to know why the pattern in species I hadn’t observed being magicked up was one consistent with common descent on the grand scale.

    You seem particularly to struggle with the logic of this position, as I have repeated it several times and you have mangled it back at me several more.

  26. stcordova: That rift will continue until Evolutionary Biologists adapt to new data and provide a nnew generation ad hoc, flimsy, and incoherent explanations.

    Yeah! I’m waiting for that nnew generation of ad hoc, flimsy, and incoherent explanations.

  27. stcordova,

    No I don’t, but I was pointing out how badly evolutionists need to have absence of functional constraint to make their theory coherent.

    That is clearly untrue. Many parts of many proteins are clearly under quite severe functional constraint. Enzyme active sites and cofactor binding sites for a start, but this is actually even more true in non-enzymatic proteins – ubiquitin, for instance, whose very ubiquity constrains change. Histones ditto. You are trying to argue from specific cases – parts of sequence that are under constraint – to a general case that all of sequence is under constraint.

    Even under pain of eternal damnation, I don’t buy that argument.

  28. Of course Sal rejects any phylogenetic evidence for lack of constraint, which implies that he thinks every species was separately created. Because if there were kinds with multiple species, we could compare sequences among species to discover that there isn’t much constraint on most of them. I wonder if Sal will ever admit that.

  29. Allan,

    No, you really aren’t getting it. I don’t want HGT to be an ‘instance of descent’. I’ve said this a few times now. HGT is one of the paths by which sequences travel, from their common ancestor (a sequence, not an individual or a species).

    You’re contradicting yourself. Earlier you wrote:

    You appear to want to restrict the term ‘common descent’ to vertical inheritance. And hence, in that context, HGT is noise at the point of injection, signal after. But in fact ‘common descent’ should, IMO, apply to any sequences that can trace back to a single ancestral sequence, regardless of the path taken.

    Rather than bundling HGT within “common descent”, I think it makes much more sense to maintain the vertical/horizontal distinction and exclude HGT from common descent.

    Nothing is lost by doing so, and an important distinction is maintained.

    We can still discuss the full history of a sequence that experiences HGT. It descends with modification in the donor lineage; then the HGT event occurs; then it descends with modification in both donor and recipient lineages. The HGT event itself is not an instance of descent.

  30. Alan Fox,

    So, are you accepting that the earliest trilobite fossils date from deep in the Cambrian, maybe 520 million years ago? Earlier fossilised tracks hint at trilobite ancestors without armoured exoskeletons.

    Accepted

  31. Mung: Why?

    Oh look. Some tracks. Whoever made them must have evolved into a trilobite.

    Oh look. No tracks .There is no evidence of a predecessor to a trilobite

  32. Mung,

    Oh look. Some tracks. Whoever made them must have evolved into a trilobite.

    Good point, Alan is grounded in the idea of common descent as an a priori assumption. My main acceptance here is a 4.5 billion year old earth.

  33. Mung, Bill,

    Read for comprehension.

    The question was whether Bill accepted the existence of fossilized trilobites from about 520 million years ago:

    So, are you accepting that the earliest trilobite fossils date from deep in the Cambrian, maybe 520 million years ago?

    The tracks came earlier, but the question was not about those:

    Earlier fossilised tracks hint at trilobite ancestors without armoured exoskeletons.

  34. colewd: Mung:

    Oh look. Some tracks. Whoever made them must have evolved into a trilobite.

    Good point, Alan is grounded in the idea of common descent as an a priori assumption.

    My point in mentioning earlier tracks was to indicate we aren’t likely to find direct evidence of the earliest common ancestor of the trilobite clade as armour [the hard parts that make trilobite fossils so widespread]* is only going to evolve under selective pressure. First you have your organism, second you have it’s predator, then you have defence.

    My main acceptance here is a 4.5 billion year old earth.

    OK but that isn’t hugely important other than the Earth is old enough for the trilobite dating. Are you going to accept fossil dating from surrounding rocks, radiometric methods and index fossils?

    ETA* plus trilobites appear to have been exclusively marine and the marine environment is much more conducive to fossil formation than land.

  35. keiths,

    You’re contradicting yourself. Earlier you wrote:

    There is no contradiction there – certainly as I read my own words, and knowing the intent behind them. Perhaps a few qualifiers would have aided clarity, but the second passage reflects the same intent as the first – that the concept ‘common descent’ should not be restricted to [sequences that pass through] vertical inheritance.

    To take a case in point, there is a retroviral sequence that pops up in cats. It is present in all the smaller cats, but none of the larger. It appears to have been transferred from an ancestor of baboons after the initial divergence of the two clades. So, the Creationist has a few things to explain there – the ‘Common Design’ reason for that sequence’s presence and absence in the cats, and in the primates, but also the ‘Common Design’ reason for the identities of the sequence itself within families of retroviruses, which themselves show a relationship with families of retrotransposon.

    Rather than bundling HGT within “common descent”, I think it makes much more sense to maintain the vertical/horizontal distinction and exclude HGT from common descent.

    That’s a semantic preference to which you are entitled, but I don’t see the point of making life easy for the Creationist, here, and giving them an entire arena they can exclude from explanation as per the thread title.

  36. Allan Miller:..as I read my own words, and knowing the intent behind them.

    To enable you to include all the necessary caveats, you need better mind-reading powers than some use to criticize what you didn’t intend to say. 😉

  37. colewd: Alan is grounded in the idea of common descent as an a priori assumption.

    Of course that is what I think. But all I’m hoping to do in this instance is examine the age, location and morphology of trilobite fossils to see if there is evidence that falsifies the model of a nested hierarchy. Just asking that we look at the available evidence together.

  38. Alan,

    To enable you to include all the necessary caveats, you need better mind-reading powers than some use to criticize what you didn’t intend to say.

    Your criticism backfires, as usual. What led me to detect the contradiction was that I paid attention to what Allan actually wrote, instead of mind-reading.

  39. Mung: Why?

    Oh look. Some tracks. Whoever made them must have evolved into a trilobite.

    Nice question actually. The answer is that those tracks simply resemble those of later trilobites.

    In fact, in the pre-Cambrian fossil record, there are no trilobites, but there are trace fossils which very closely resemble those made by trilobites, suggesting that before trilobites developed their hard calcite shells, their ancestors were crawling about leaving traces.

    were you never with the boy scouts?

  40. Allan,

    There is no contradiction there – certainly as I read my own words, and knowing the intent behind them. Perhaps a few qualifiers would have aided clarity, but the second passage reflects the same intent as the first – that the concept ‘common descent’ should not be restricted to [sequences that pass through] vertical inheritance.

    I can only go by what you’ve written, and there is a clear contradiction between including and excluding horizontal transfers as part of ‘common descent’.

    Here you disagree with my exclusion:

    You appear to want to restrict the term ‘common descent’ to vertical inheritance.

    Here you agree with it:

    I don’t want HGT to be an ‘instance of descent’.

    I think it should be excluded, for the reasons I gave earlier.

    As for this:

    the concept ‘common descent’ should not be restricted to [sequences that pass through] vertical inheritance.

    ‘Common descent’ is a process, not a sequence. And ‘commonly descended’ sequences are those that pass from ancestors to descendants; that is, all of them. Are you aware of any sequences that are exclusively transmitted horizontally?

    A sequence may or may not have been horizontally transmitted during its history. The point is that it is ‘commonly descended’ by virtue of descent, not by virtue of any horizontal transfers it may have experienced.

  41. keiths:

    Rather than bundling HGT within “common descent”, I think it makes much more sense to maintain the vertical/horizontal distinction and exclude HGT from common descent.

    Allan:

    That’s a semantic preference to which you are entitled…

    It’s also the overwhelming preference of the biological community, judging from the way the term is used in practice.

    …but I don’t see the point of making life easy for the Creationist, here, and giving them an entire arena they can exclude from explanation as per the thread title.

    You’re granting way too much power to the creationists if you think we should redefine ‘common descent’ on account of their potential exploitation of a thread title.

    Besides, excluding HGT from common descent doesn’t help them. The phenomenon is still there, just as I described it:

    Nothing is lost by doing so, and an important distinction is maintained.

    We can still discuss the full history of a sequence that experiences HGT. It descends with modification in the donor lineage; then the HGT event occurs; then it descends with modification in both donor and recipient lineages. The HGT event itself is not an instance of descent.

    None of that gets creationists off the hook or allows them to “exclude an entire arena from explanation”.

  42. Mung: Why?

    Oh look. Some tracks. Whoever made them must have evolved into a trilobite.

    colewd:
    Mung,

    Good point, Alan is grounded in the idea of common descent as an a priori assumption.My main acceptance here is a 4.5 billion year old earth.

    Notice the selective acceptance of tracks at work here.

    IDcreationists are all up in arms about purported tetrapod tracks that predate the Tiktaalik fossil. There’s no fossil or anything, just some fossilied mud-imprints that could be tetrapod feet.
    IDcreationists believe these tracks are from a true tetrapod with with a psychosis-level of conviction, entirely and only because they seem to mess up the chronology of the fossilt transition from lobe-finned fish to tetrapods.

    I’ll take this opportunity to mention that there are transitional-tetrapod trackways predating the tetrapod-tracks that predate Tiktaalik, but you’ll never hear IDcreationists mention this. No doubt IDcreationists would again selectively decide to disbelieve the even older transitional trackways.

    Now we a similar situation with Trilobites. Trackways that look like the ancestors of trilobites, yet creationists will selectively decide to reject trackways now that they fit the evolutionary chronology.

    You have a double standard gentlement, and you’re not even aware of it. You are so deeply and intensely biased and it shows.

  43. Alan Fox: Are you going to accept fossil dating from surrounding rocks, radiometric methods and index fossils?

    A geologic strata isn’t actually dated with index fossils, it is merely recognized as being a particular strata because of the fossils it contain. The dating of sedimentary rock is from surrounding rocks and radiometric methods.

    Just wanted to point this out because creationists mistakenly think that geologic strata and fossils are dated by circular reasoning: This layer contains this fossil, therefore it is X millions of years old. This fossil was found in this layer, and this layer is X millions of years old. How do you know the layer is that old? Because it contains this fossil. <- That's how creationists think "dating by index fossils" works. It isn't.

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