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Are we in the midst of the sixth mass extinction?

  1. Jan 15, 2004 #1

    Nereid

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    Over on the Politics & World Affairs sub-forum, in a thread called climate risk 'to million species'*, I asserted that the Earth is the midst of the sixth mass extinction**. There was some disagreement, so I suggested that we apply the scientific method, and test the assertion. More discussion, much agreement, ... and here we are.

    So, my proposal:
    1) We all agree on what constitutes a mass extinction.

    2) Bystander and Russ propose a definition of the 'normal' or 'background' extinction rate; we discuss it and agree.

    3) We agree on what the actual background extinction rate has been, up to 1mya.

    4) I propose a means of estimating the present extinction rate; we discuss it and agree.

    5) I will make an estimate of the present extinction rate; we discuss it.

    Supplementary topic: if we agree that number six is in progress, then we look for causes.

    Some other 'rules':
    + we establish our protocol before we begin the work; that's 1 through 5 above, plus these 'rules'
    + we restrict ourselves to peer-reviewed sources (which we post a link to, if possible)
    + I will try to keep us on track, and move us along to the next item when we're ready (I'm happy for someone else who we trust to take this role, if Bystander, Russ, Ivan or SelfAdjoint is uncomfortable with me taking it). Of course, Monique and Another God will keep us all honest :wink:

    *Here's the thread:
    https://www.physicsforums.com/showthread.php?s=&threadid=12280

    As this may be new to the denizen of Biology, let's add a 0):
    0) two days for questions, suggestions (on the protocol!), etc before we start.

    **The widely accepted 'five mass extinctions' occurred at the end of the Ordovician, Devonian, Permian, Triassic and Cretaceous (bye-bye dinosaurs).

    [Edit: fixed typo]
     
  2. jcsd
  3. Jan 16, 2004 #2

    russ_watters

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    I'm not sure how exactly you plan to start, but do you have any info about those 5 mass extinctions? An account of them may help with #1.
     
  4. Jan 16, 2004 #3

    Bystander

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    Second on the summaries. If someone would care to throw in a quick heirarchy of kingdom, ..., ..., family, genus, species, it'll save me enormous embarassment.

    Re. "rates," might I suggest we look at four? "General rates for appearances/emergences and extinctions of wide-ranging/widely distributed species, and the same pair of 'pocket/isolated/enisled/marooned rates' for special environment cases, Lake Victoria, Galapagos, etc.?"
     
    Last edited: Jan 16, 2004
  5. Jan 16, 2004 #4

    selfAdjoint

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    If we're going to look for a Great Extinction, we need

    (a) total number of species existing at the start of whatever period we pick (Quaternary? Holocene? Post-Glacial? Last 25,000 years?)

    (b) Count of species gone extinct during period.

    (c) An agreed on figure (proportion of existing species gone extinct) that will constitute a Great Extinction.

    As long as we refrain from over-hastily attributing cause, that should enable us to establish the fact or otherwise of the Sixth Great Extinction hypothesis.

    I hope we can hold to the schedule laid out above by Nereid, and if we do I think we will have something trustworthy.
     
  6. Jan 16, 2004 #5

    Phobos

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  7. Jan 16, 2004 #6
    I think we are headed, soon, towards a new Earth and Heaven??
     
  8. Jan 16, 2004 #7

    Bystander

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    More for the reading list: Google "david raup" + "extinction rate" and "michael foote" + "extinction rate" --- couple dozen sites for each. Raup took off on the "Nemesis" hunt after Alvarez pointed the world's attention toward catastrophism, but he did some decent analysis of "extinction events" along the way.
     
  9. Jan 17, 2004 #8

    Ivan Seeking

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  10. Jan 17, 2004 #9

    Nereid

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    King Phillip called out for good soup

    Kingdom
    Phylum (Division for plants)
    Class
    Order
    Family
    Genus
    Species

    Here's one readable overview:
    http://www.wordiq.com/cgi-bin/knowledge/lookup.cgi?title=Class_(biology)
     
  11. Jan 17, 2004 #10

    Nereid

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  12. Jan 18, 2004 #11
    A very creative hypothesis of Richard Muller is the relation between mass extinctions and the close encounters of a possible twin star Nemesis.

    http://muller.lbl.gov/pages/lbl-nem.htm

    Incidentely, a bit of a contrast, We may be in a mass extention phase indeed but not because of human actions. The events that constitute the Younger Dryas - Pre Boreal boundary 11,570 years ago, caused dozens of mega fauna species (mammots etc) to become extinct. In the mid Pleistocene, one million years to 600,000 years ago, I believe about a quarter of the oceanic foraminifea became extinct. It may have gone unnoticed by the public, but it got the oceanic biologists rather excited.

    So whatever the Pleistocene has been doing to Earts biota, it may continue that way for millions of years more without the help of mankind. Palaeonthologists of hundreds of million years in the future may only recognise a single mass extinction.

    On the other hand the explosion of evolution of some species in the past 10,000 years like the African Lake Malawi and Lake Victoria cichlids may compensate for the loss of other species and the total count of species may be still increasing.

    And BTW, I don't think that this is science, rather hype forming propaganda:

    http://news.bbc.co.uk/1/hi/sci/tech/3375447.stm
     
  13. Jan 18, 2004 #12

    Nereid

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    Step 1: Agree on what constitutes a 'mass extinction'

    Two days are up, no substantive suggested changes to the protocol (thanks for the support).

    1) We all agree on what constitutes a mass extinction.

    Which level(s) do we look at?
    Kingdom, Phylum/Division, and Class may be too broad (few exist, very few - none? - have gone extinct in one of the big 5)

    Species and Genus may be too narrow (how to count them all? make robust estimates?)

    -> focus on Order and Family, with appropriate consideration of Class and Genus. Yes/No/Maybe?

    Which environments do we consider?
    Those which leave copious numbers of fossils (e.g. shallow marine) may be better than those which don't (e.g. alpine) Does it matter that we are somewhat equivocal in how we include some environments (e.g. tundra)? or some taxa (e.g. soft invertebrates, fungi, algae)?

    I'd love to trace the (non-)extinctions of my namesakes, but I suspect there'll be little fossil data to use :wink:
    http://www.pmel.noaa.gov/vents/nemo/explorer/bio_gallery/biogallery-Info.00054.html
     
  14. Jan 18, 2004 #13

    Ivan Seeking

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    Re: Step 1: Agree on what constitutes a 'mass extinction'



    This seems to be consistent with the references.

    Why choose by environment? Is this intended to narrow the field for comparison?
     
  15. Jan 19, 2004 #14

    Bystander

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    Re: Step 1: Agree on what constitutes a 'mass extinction'

    Species (cross fingers, knock on wood) --- tough as that is in the fossil record.
    Long as there is a continuous record before, through, after the event(s) we examine (major extinctions), I'd say look at whatever we can get our hands on, characterize it as sampling some "environment type" during an extinction event, and see if my hypothesis that there ain't no Lakes Malawi, Victoria, Tanganyika, Hawaiian chains, Galapagos, or Andean ridge ecologies showing up in the fossil record holds any water.
     
  16. Jan 19, 2004 #15

    Nereid

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    Primarily to ensure there's a big enough base from which to calculate a background rate that we will have some confidence in. I certainly don't want to limit the scope, but am not sure how critters which came and went without leaving a record (that we have been able to see so far) can be incorporated into our work otherwise.
     
  17. Jan 19, 2004 #16

    Nereid

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    Would you consider restricting this to just eukaryotes? Even there, how do we address the fact that there are widely differing estimates of the number of species of multi-cellular organisms, in most of the major Classes (think of Insecta)?
    If we choose to set these aside, aren't we automatically discounting "widespread loss of 'island' ecologies" as a potential cause of a mass extinction (no matter how such a loss came about)? Otherwise I think it's a very sensible place to start.
     
  18. Jan 20, 2004 #17

    russ_watters

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    Oy - I have some homework to do...
     
  19. Jan 20, 2004 #18

    Ivan Seeking

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    That's what I keep saying.

    I feel like a goldfish in a school of Tuna.
     
  20. Jan 21, 2004 #19

    Bystander

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    No "fossil rate" to compare 'em to, at which point, we can assume or assert any number of things: 1) there have been no isolated systems in the past, and the fossil background rate is valid as is; 2) the number of isolated systems in the past has been equivalent to what we see today, and the disappearances of those systems contributed in no way to the background rate (all organisms were integrated into the general/global system); or, 3) an equivalent number of isolated systems that disappeared without trace, and without net contribution to the number of species (comparing initial appearance of system to its disappearance).

    Lake Victoria is my overworked case in point --- 400 appearances in 14000 years, and how many species in its previous live lake-dead lake cycles over the past million? Four hundred cichlids gone, but also appeared, for a net zero as far as the scoreboard goes. The isolated environments have got to be contributing a net increase in number of species over the past billion years, but the rate at which they contribute is a little tough to estimate. As far as extinctions of isolated ecologies, when they disappear, they don't take the original populations of the pioneering species with them --- "Victoria dies" does not imply the collapses of Malawi and Tanganyika cichlid populations, nor S. Amer., and points west. Tropical fish hobbyists (including me) ain't happy with the Nile perch, nor the geniuses who introduced it, but in the long run, the lake's a goner, and the Victoria cichlids are goners (barring a wet enough climate to overflow the lake into other drainage basins prior to its drying out again).


    quote:
    --------------------------------------------------------------------------------
    Originally posted by russ_watters
    Oy - I have some homework to do...
    --------------------------------------------------------------------------------



    That's what I keep saying.

    I feel like a goldfish in a school of Tuna.

    Mackerel, sharks, bluefish --- this is gonna be fun if the workload doesn't kill us all.

    Edit: Horribly long-winded way of saying that inclusion of currently observed rates of extinctions of isolated species "automatically discounts" contributions of the same effect in the fossil record due to the fact that they are too insignificant to be observed there.
     
    Last edited: Jan 21, 2004
  21. Jan 21, 2004 #20

    Nereid

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    Concrete proposal for step 1

    Thanks everyone for the inputs.

    Recap: step 1 is "We all agree on what constitutes a mass extinction."

    How about:
    a) it's rapid; takes place in < 100,000 years
    b) it's widespread; extinction is seen in different phyla and divisions, in widely different locations (not islands), and many different habitats
    c) a significant fraction of all species (>60%) and families (>10%) go extinct.

    For b):
    - select 3 from the 'big 9' animal phyla (I've got my favourites; you take your pick; link:
    http://ebiomedia.com/gall/awob/)
    - select 3 from the 13 divisions of plants (link:
    http://en.wikipedia.org/wiki/Plant)
    - if our choices take us to 'insufficient data', we'll reconsider the choices

    For locations and habitats, I don't have a proposal - can someone help out?

    For c): since we can't count all species (nor families?), we should agree on a robust method for making estimates.

    Yes/No/'I've got a better idea'?
     
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