Are we in the midst of the sixth mass extinction?

[Evo]

Check out this interactive atlas!

The first link is an article explaining some of the things you can pull from it.

"An interactive atlas of the world's natural wealth paints a graphic picture of humanity's inexorable spread.

It shows that since 1850 humans have affected almost half the planet's land.

Entitled the World Atlas Of Biodiversity: Earth's Living Resources For The 21st Century, it is the work of the United Nations Environment Programme World Conservation Monitoring Centre (Unep-WCMC), based in Cambridge, UK.

It has been collated from the centre's research, the work of independent scientists, and governmental and other reports.

The centre says the data will be made available to users by a unique interactive mapping service accessible from the Unep-WCMC website.

This will let them create their own maps comparing subjects from wilderness density to human population.

http://news.bbc.co.uk/1/hi/sci/tech/2166306.stm

The atlas - http://stort.unep-wcmc.org/imaps/gb2002/book/viewer.htm

 

[Nereid]

Good to see that no one missed me

This thread has moved along quite nicely these last couple of weeks, tho' I'm a little curious as to why Russ has deserted us, and why (if?) "*SNIP You're not a biologist, I'm not a biologist, and the biologists seem to be avoiding this thread in droves." Do they know something we toy scientists don't?

Anyway, while I come up to speed, an open AP from before - choice of three Divisions of Plantae - a modest suggestion:
- Pterophyta ("ferns")
- Pinophyta ("conifers")
- Magnoliophyta ("flowering plants")
(one ref: http://en.wikipedia.org/wiki/Plant)

... and a couple of snippets:
- defining a species is tricky; if biologically defined (crudely, can't interbreed), then the often easy hybridisation in plants poses a problem; if morphologically defined (crudely, looks different), then how to deal with the many which do look different but aren't (and vice versa)
- however you define 'species', Ivan's question hurts - no appearances of new species (except for all those pathogens we've created with our misuse of anti-biotics)
- it's certainly good fun to look for sources of mass extinctions among the stars, but IMHO they're a tad desperate (except our friend the KT, and possibly the Ordivician); plate tectonics is probably enough. Let's leave this till later in the process.

Back soon.

 

[Nereid]

Biologists - help please!

Originally posted by Bystander
Might as well continue with the agenda? Structured inquiry doesn't seem to be quite as stimulating as a political debate.

p.s.--- "ecosystem classification" doesn't appear to be an "exact" science.

http://modis-atmos.gsfc.nasa.gov/ECOSYSTEM/
http://srmwww.gov.bc.ca/cdc/sei/sunshinecoast/classification.htm
http://www.environment.govt.nz/info/froude/env-class/page29.html
http://www.colby.edu/~ragastal/GE251/Paleoecology.htm
http://biogeo.nos.noaa.gov/products/hawaii_cd/htm/refer.htm

Third link looks quite interesting; pity it's only a draft (second link is dead).

Call to all real biologists/ecologists - can you help us please? We're looking for a link or two to a widely accepted, reasonably robust classification system for ecological systems.

 

[Nereid]

Bystander wrote: 30%? 1Ma? Three a year? I can live with that.

Am not sure I follow the logic - we're assuming there are only 10 million species total in our 3 animal phyla and 3 plant divisions? Or you're doing an OOM (order of magnitude) check that the number seems vaguely sensible? Or Monty Python ('now for something completely different')?

 

[Bystander]

Just order of magnitude.

Dead links this soon? "Mass web extinction?" I really did try to pick some that looked "permanent."

Edit: 10M, 1Ma. and 3 net species extinctions/a are "boundaries" for what I can live with as the definition of an "event" that needs to be examined.

Looks like that's going to be so far below noise levels as to be undetectable; you want a higher net rate, that's cool. The gross rates are starting to look like a real problem --- we're going to be trying to pick very small differences from two very large numbers and average them over time --- ugly.

 

[Evo]

Nereid, I posted an article on new species recently found in answer to Ivan's question, you may want to go back and take a look.

Here are a couple of links that I think you may find helpful.

World Research Institute

http://www.wri.org/wri/biodiv/b02-gbs.html

Their EarthTrends portal with ecosystem information

http://earthtrends.wri.org/

An excellent excerpt - Conservation Biology, this is full of great information including species extinction numbers "Declining biodiversity is a serious problem: officials at the U.S. Fish and Wildlife Service estimate that more than 500 U.S. species have gone extinct during the past 200 years. Of these, roughly 250 have gone extinct since 1980."

http://www.mhhe.com/biosci/genbio/tlw3/enhancement_chapters/conservation.html

Biomes

http://www.ucmp.berkeley.edu/glossary/gloss5/biome/index.html

An article on another atlas, unfortunately I think it is only in book form, but looks interesting.

http://news.bbc.co.uk/1/hi/in_depth/sci_tech/2001/san_francisco/1172896.stm

 

[Rader]

Originally posted by Nereid
Third link looks quite interesting; pity it's only a draft (second link is dead).

Call to all real biologists/ecologists - can you help us please? We're looking for a link or two to a widely accepted, reasonably robust classification system for ecological systems.

Online Databases
http://www.nabt.org/sub/htdi/v62n02p124.asp

Terrestrial Ecosystem Monitoring Sites
http://www.wsl.ch/rauminf/riv/datenbank/tems/database_tems.html

 

[Nereid]

Bystander wrote: N₀ = k_app,ave(1-3Ga) - k_ext,ave(1-3Ga),
and using 10M as a round number for the current species count, we get
k_app,ave - k_ext,ave = 0.01 - 0.003 species per year. That is, the average NET rate of change in number of species is equal to the difference in the average appearance and extinction rates. Talk about trivial statements of the trivially obvious --- we get no absolute estimates for these rates without appealing to other estimates of the total number of species that have existed, 100-1000 times the currently existing number, or 1-10G appearances in 1-3 Ga, an average appearance rate of 0.3 - 10 species/a. The average extinction rate is then (0.3 - 10) - (0.01 - 0.003).

Approach #2: same game as 1, and subscripting N with number of Ma prior to present to indicate the number of species just prior to the extinction events, using the dates and estimated extinctions from Thomas,
N₀ = 0.35N₆₅ + (k_app - k_ext)65Ma,
... (the eqtns for Triassic, Permian, and Devonian events are left as an exercise for the reader)
N₃₇₀ = 0.35N₄₄₀ + (k_app - k_ext)70Ma,

and, invoking a suspected 6th Cambrian event with a 50% loss as a guess,

N₄₄₀ = 0.5N₆₀₀ + (k_app - k_ext)160M,

and, finally, N₆₀₀ = 1 + (k_app - k_ext)(400 to 2400Ma).

This removes extinction losses from the average extinction rate; the suspected Cambrian event's inclusion further reduces the background extinction rate. Working backward through the equations, substituting the last, for N₆₀₀, into that for N₄₄₀, and into ta-da, ta-da, we get

N₀ = 6 x 10^-4 + (130-140 Ma)(k_app - k_ext). The difference between the appearance and background extinction rates has increased from 0.003 - 0.01 to 0.07 - 0.08/a ; still no real insights regarding magnitudes for the gross appearance and extinction rates.

I've been a little distracted by a discussion on the Social Sciences sub-forum, and am only now getting back to this one; sorry.

Thanks to Evo and Rader for some excellent links and resources; any comments from Bystander? Ivan? Russ?? (seems we've lost Russ).

Bystander, I'm in the slow class today, and I don't really follow what you wrote. So I re-worked it, using just 1Ga, and units that I'm more comfortable with (I can see Andre shaking his head [b(]; he had just begun to form a favourable impression of me ):

Number of species today = Number of species which appeared over the past 1 billion years minus the number which went extinct in this same 1 billion years.

If we assume that there are 10 million species today, then there have been, on average, 0.01 net new species per year, over the past 1 billion years.

Of course, 10 million is almost certainly the difference between two much larger numbers, {though I can't see how Bystander got one of the numbers to be ~1 billion }

In approach #2, we plug in estimates of the number of species lost in each of the five mass extinctions:

Number of species today = 35% of those present before the KT event + the number of net new species in the last 65 million years; the latter we assume to be the background new species rate (per year) times the number of years (65 million).

Similarly for the Triassic, Permian, and Devonian mass extinctions, using species survival data from Thomas. {I'm not sure which 'Thomas' Bystander is referring to - Chris Thomas, of Britain's University of Leeds perhaps? and what are the percentages of species which survived each mass extinction?}

Number of species just before the Devonian mass extinction = 35% of those present before the Ordovician event + the number of net new species in the 70 million years between the Ordovician and Devonian mass extinctions; the latter we assume to be the background new species rate (per year) times the number of years (70 million).

Then, including a postulated early Cambrian event which wiped out 50% of the species at the time:

Number of species just before the Ordovician mass extinction = 50% of those present before the Cambrian event + the number of net new species in the 160 million years between the Cambrian and Ordovician mass extinctions; the latter we assume to be the background new species rate (per year) times the number of years (160 million).

Finally, just before the Cambrian mass extinction:

Number of species just before the Cambrian mass extinction = 1 (the original species!) + the number of net new species in the 400 million years between the origin of species and Cambrian mass extinction; the latter we assume to be the background new species rate (per year) times the number of years (600 million).

The difference between the rate of appearance of species and the rate of extinction of species is then obtained by simple algebra from the above.

Bystander, please correct anything which is substantially incorrect, in terms of a re-statement of your point.

Nereid

[Edit: formats and added Bystander's conclusion]

 

[Bystander]

Ellen (?)Thomas, one of the early links posted; if we've got 10M species at present, and we take the "estimates" in the links that there have been 100 -1000 extinctions for everything we see today, that gives us rough numbers for the first approach.

Otherwise, looks like you've got the gist of things --- mostly an attempt to "fence" some of the numbers in a little --- none of this qualifies as limits or boundary conditions on a problem statement.

I've been going to play the same game with the categories listed in the "earthtrends" link evo posted --- not far enough up "the list" at the moment (or, I've not worked far enough down). Doubt there's data enough to get past the KT event.

 

[Andre]

Nereid, you said:

(I can see Andre shaking his head ; he had just begun to form a favourable impression of me

Don't worry, I have a positive idea about people, especially when they show common sense and like reasoning.

As you know, I'm working on an rather extreme idea and I'd like people with a lot of common sense to judge me.

As far as this extinction is concerned, what woulds be the impression of the geologic explorer of 63 My in the future, He will unable to discriminate the Foraminifera extinction of the mid Pleistocene (7-900 Ky ago) with the megafauna extinction (11,760-3700 years ago. Simply because it's to close together looking at million years in the future. Let alone the expected extinction due to climate and/or due to antropogenic biotope destruction or other causes. And if we have no good clue on the http://town.morrison.co.us/dinosaur/extinction/meteor.html the current situation may not be that logical at all. What I'm trying to say it that the Palaeotologist of 63 My years ago could tell a totally different witness story than we could imagine today. As we -in our turn-, we could tell the paleontoloogist of 63 My in the future that there was not a concentrated mass extinction at all, just an array of coincidences, unusual oceanic current changes for the mid pleistocene foriminifera extinctions and climatical upheaval in the late Pleistocene/holocene boundary for the Megafauna extinction and finally all kind of Anthropogenic reasons for thecurrent alleged extinction wave.

Well not really that alleged, we lost the Dodo (1755) the Giant Moa (1773) the Elephant Bird (17th century) the Cape Lion (1885) the Tarpan (1879) the Quagga (1883) the Great Auk (1844) the Passenger Pigeon (1914) the Carolina Parakeet (1914) 27 species birds became extinct between 1927 and 1944, Moreover, the Barbary Lion (1920) and the Tasmanian Wolf (date unkwown)

Just atempting to show that even mass extinctions may be a lot more complicated.

 

[Nereid]

Thanks for the kind words Andre.

There are an awful lot more megafauna extinctions to include; a partial list, from memory:
- many, many other Pacific island extinctions, esp of birds (however, per Bystander, the extent to which any individual island ecologies show up in the fossil record is an open question)
- North (and South?) American and Australian megafauna extinctions - the timing appears to coincide with the arrival of a particularly destructive animal (Homo sap.), which may also have contributed to widespread climate change (the Tasmanian tiger was one of the last, lucky survivors; there was a rich collection of marsupials - 'lions', kangaroos, ... - that died out; the introduced dog ('dingo') may also have contributed to the extinction of hundreds of species of smaller marsupials).

Bystander, I resonate with the 'working down the list'; my prioritisation includes 'can address in a few minutes' (gets to be high on the list, almost irrespective of importance). Thanks for you clarifications.

 

[Bystander]

Correction: Evo's link is the following (don't think this copy works),

http://www.mhhe.com/biosci/genbio/t...nservation.html, and I'd feel so much better about using the species counts in the various categories if the site did not also include the following, "Prairie dogs once roamed freely over 100 million acres of the Great Plains states, but are now confined to under 700,000 acres (table 31e.6)." 700,000 acres?! I'm reasonably certain that there are single "dog towns" that size and larger in CO, NM, WY, KS, OK, TX, and maybe Nebraska. 700,000 sq. mi.? Probably not --- 70,000 might be about right (45 million acres for the math impaired).

The data problem is going to kill this project.

 

[Andre]

Nereid

North (and South?) American and Australian megafauna extinctions - the timing appears to coincide with the arrival of a particularly destructive animal (Homo sap.), which may also have contributed to widespread climate change

I gues that the role of the Clovis people in the megafauna extinction at the Holocene boundary and and their arrival in America is highly disputed. I gues you could fill a modest library in the dispute about ill, chill, or kill.

There is some evidence that humans were present in North Siberia in the mid Pleistocene but they may not have reached Beringia before the Holocene. Moreover Argentinian early aecheologic sites date back to roughly the same period, suggesting that other migration routes may have been likely also (remember Thor Heyerdahl). All this is feeding the objections to those popular hypotheses. Moreover, the few spearheads found on paleonthologic findings in relation to sites with absence of that evidence, are making it very hard to associate the human appearance with many extinctions. Most certainly not the megafauna extinction of North Siberia, where arid grassy steppes seemed to have changed to moist peat swamps about overnight. Too much for the Mammoths to cope with.

 

[Nereid]

Andre wrote: I guess you could fill a modest library in the dispute about ill, chill, or kill.

Too right mate .

Perhaps the Australian case is more clear cut?

Bystander wrote: The data problem is going to kill this project.

That may turn out to be the case (perhaps that's why Russ bailed out on us?), but I think we can at least put good bounds on #6 (yes or no).

 

[Andre]

Too right mate

:D
Nope, it aint.

http://www.utah.edu/unews/releases/01/jun/australia.html

We found that the disappearance of the large animals in Australia seemed to occur in a very short time interval 46,000 years ago, which is 10,000 to 15,000 years after the arrival of humans.

Perhaps indeed but

Ayliffe doubts the early human population was large enough to hunt large animals to extinction quickly, meaning in hundreds of years. She believes early humans - nomadic hunter-gatherers who were the ancestors of modern aborigines - gradually destroyed animal habitat by setting fires to drive game into the open, and that the habitat loss ultimately led to mass extinction over thousands of years.

There is evidence of increased frequency of fires at the time of extinction," she said. A small number of people "can set fire to a large area of land, which renders that area unusable for the animals.

It appears that being a paleothologist not automatically qualifies for environmental science. The role is forest fires is much more complicated. Forest fires are and integral part of the natural balance. You can't set fire to something that was burned recently and if something is going to burn anyway, dry lightning will do it for you eventually, regardless if there where vicious people, seeking to destroy their own habitat. So this line of reasoning can be disputed. It will not however, because it supports the alleged evilness of mankind and that seems to be very popular these days.

However, we are part of the nature, not an enemy and we are certainly not capable to destroy it. Relax.

But could there be a natural geologic cause of the Australian extinctions? The only geologic events that come into mind are the Dansgaard-Oeschger events that- together with the Clathrate gun hypothesis (Kennett et al 1999)-may have been the trigger of a most unusual scenario. Thinking about it.

 

[Bystander]

"#6? Yes or no?" Mebbe --- I ain't quit yet --- signal:noise is starting to look like one tough problem.

 

[Nereid]

Originally posted by Bystander
"#6? Yes or no?" Mebbe --- I ain't quit yet --- signal:noise is starting to look like one tough problem.

Wasn't it always going to be? That's partly why I think it's well worth the effort to look at this one in some detail.

(In case regular readers hadn't already noticed, I've been rather consumed by a series of discussions in Social Sciences; I just can't help myself there. If you've opinions too, please don't be shy. I really want to keep this thread going, and will put the time in when I can).

 

[Bystander]

To the bitter end. However, I'm stuck at the moment for ways and means to detect 2-3 new species within the 10k or so new identifications per year (consistent with 2-3k appearances per year globally, if we apply a first order rate model to the Lake Victoria cichlids, and extrapolate that to the 10M estimate for total extant species). Doesn't look to be demonstrable, leaving me to argue from order of magnitude rate estimates vs. demonstrable disappearances.

 

[Nereid]

I've got a couple of difficulties with Bystander's approach, apart from the ones he (she?) has already identified:
- a background rate of extinctions that is constant through all between-mass-extinction pairs would seem unlikely. Suppose we got a clear answer at the end of our quest, and the loser was sore; a simple challenge would be 'but the background rate in the pre-Cambrian was quite different than that from 65Mya to 1 Mya!'
- much more difficult - since estimates of the number species of unicellular organisms is at best, very poorly constrained - the two numbers we'd be taking the difference between could be much larger than two or three orders of magnitude.

Avoiding these kinds of problems was partly why I suggested limiting ourselves to a) multicellular critters, and b) only some well-defined subset of all such.

Could I suggest a little side project? What does the fossil record of the last 65 million years say about the prevalence of chordates and magnoliophyta?

 

[Bystander]

Originally posted by Nereid
- a background rate of extinctions that is constant through all between-mass-extinction pairs would seem unlikely.

Uh-huh --- and the distribution of rates about the average is unknown, leaving us in unknown territory as far as stating that an observed rate is not only "high," but of a magnitude that it may be accorded "event" status.

- much more difficult - since estimates of the number species of unicellular organisms is at best, very poorly constrained - the two numbers we'd be taking the difference between could be much larger than two or three orders of magnitude.

Again, uh-huh --- we have no idea what "high" rates are.

Avoiding these kinds of problems was partly why I suggested limiting ourselves to a) multicellular critters, and b) only some well-defined subset of all such.

"Well defined" is going to be open to interpretation: 1M + 10k new IDs/a in a 10M total estimate; some of the anecdotal, or not so anecdotal, information about salmon "picking sides" in a lake; the incomplete nature of the fossil record; and the open questions re. evolutionary mechanisms and selection mechanisms.

Could I suggest a little side project? What does the fossil record of the last 65 million years say about the prevalence of chordates and magnoliophyta?

Or, what's the "party line" on two separate families (depending upon the taxonomy to which one subscribes) evolving/selecting large, hairy, tusked, proboscidean forms during the pleistocene; i.e., just what is the official story on environments and megafauna? Low primary productivity implies megafauna? Or, high primary productivity? It comes and goes as far as fossil record appears to indicate, but what drives the appearances and extinctions of such?

 

[lab rat]

Originally posted by Ivan Seeking
Can anyone name one new species to evolve in the last 100 years?

I can name many species that have gone extinct in the same time. In other words, the times scales discussed seem much too large. If we are creating a mass exinction the applicable time scale is in hundreds of years, not thousands or millions.

Here is a blurb from an article about a new species of whale. I attached the article if anyone is interested.

June 26, 2002 - In the mid-1970s, four rare beaked whales washed ashore dead on the coast near San Diego, California. James Mead, a leading authority on beaked whales from the Smithsonian, examined the skulls of these animals and tentatively identified them as the Southern Hemisphere species Mesoplodon hectori. At that time, there were a dozen named species of beaked whales (Ziphiidae) within the genus Mesoplodon that were diagnosed primarily by the size, shape, and position of an enlarged pair of teeth in the adult males. Two decades later, Merel Dalebout a graduate student from the University of Auckland analyzed DNA sequence data and found that these California animals clustered far apart on a phylogenetic tree from the Southern Hemisphere specimens of Mesoplodon hectori. Working together, Dalebout, Mead, and co-workers are now formally describing this heretofore unrecognized new species in the current issue of Marine Mammal Science (1). The new species, Mesoplodon perrini, is named after William F. Perrin, a preeminent marine mammal systematist and conservationist.

Taken from this article
----> http://www.lam.mus.ca.us/research/mammals/beakedwhale.htm

 

[Bystander]

New? Or, newly identified? Plus, sounding like the last of their species from the description of the discovery --- is it an "appearance," or an "extinction?"

 

[lab rat]

I guess that's open to your interpretation. I read the story and a couple of related stories and [to me] it sounds like it's a new species in the last 25 years.

 

[lab rat]

Oh, Bystander, I do see your point about a few new species and many, many, many disappearing. I'm not trying to stir things up here, I just remembered hearing about the whales a couple of years ago so I posted it.

 

[Bystander]

Not arguing with you on the point --- just echoing the problem with "interpretation," definition, and whatnot that we've been running into in this thread.

It's about boiled down to two possible conclusions: 1) mine, that there is insufficient evidence to reach any conclusions (not likely to budge from it); 2) and Nereid's, whatever it may be.

Do I feel that swapping tigers for 23 new species of cane toads is a fair deal? No. Are we in the middle of a "great extinction?" "Hubris" is a twenty dollar word --- bible thumpers say, "pride" --- funding proposals are successful in direct proportion to the fear that can be generated (Manhattan Project, Cold War, AIDS) --- how many observatories and astronomers are being funded by fear of "great impactors?" Not many --- it's peanuts. How much money can be shaken from the Congressional tree by pointing out changes in flora, fauna, and climate as if they've never been observed before? Tons --- very big business. Ethics and big business? Not in my lifetime.

 

[Bystander]

Actually, we've got big problems here; none of our hypotheses are falsifiable --- I have to have an unbroken global record of species appearances and extinctions to demonstrate that N.'s assertion that the current extinction rate is high enough to count as an "event" is false, and N. has to have an unbroken record to demonstrate that my assertion that appearance and extinction rates are of the order of 10³ is false.

Stalemate.

 

[Nereid]

Bystander wrote:*SNIP Or, what's the "party line" on two separate families (depending upon the taxonomy to which one subscribes) evolving/selecting large, hairy, tusked, proboscidean forms during the pleistocene; i.e., just what is the official story on environments and megafauna? Low primary productivity implies megafauna? Or, high primary productivity? It comes and goes as far as fossil record appears to indicate, but what drives the appearances and extinctions of such?

later:

*SNIP I have to have an unbroken global record of species appearances and extinctions to demonstrate that N.'s assertion that the current extinction rate is high enough to count as an "event" is false *SNIP

Which is partly why I wanted Bystander (and Russ, but he's absconded - sure to get a bad mid-term report) to define (a method for determining) the background rate*!

But wait! Didn't we agree that there have been mass extinctions in the past (step 1 in the proposal)? If we did, how did Bystander (and Russ?) come to be comfortable with the idea that there *was* a mass extinction at the KT boundary, the late Triassic, Permian/Triassic, late Devonian, and late Ordovician?

So, to convince the most skeptical participant, how about we ask Bystander what convinced him that there were five (six, including the Cambrian) mass extinctions? Then we work together to find a way to repeat the steps - as closely as we can - for today's mass extinction (per Nereid's - and Ward's, and ... assertion)?

Hey prodigal child Russ - care to rejoin us? Andre, are you as skeptical as Bystander and Russ? Anyone else?

*My proposal, from the start of this thread:
"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."

 

[Bystander]

Appearance -extinction = 0.01 -0.1 species/a --- there isn't data to plot the difference as a function of time; there is no way to demonstrate a real time modern appearance rate; there is no way to demonstrate a modern real time difference in rates; there are no data to support absolute values of historcal/paleontological rates to much better than 2-3 orders of magnitude.

Two equations (modern extinction rate estimate), the average rate difference over geological time, and three unknowns --- the system is indeterminate.

 

[Nereid]

Originally posted by Bystander
Appearance -extinction = 0.01 -0.1 species/a --- there isn't data to plot the difference as a function of time; there is no way to demonstrate a real time modern appearance rate; there is no way to demonstrate a modern real time difference in rates; there are no data to support absolute values of historcal/paleontological rates to much better than 2-3 orders of magnitude.

Two equations (modern extinction rate estimate), the average rate difference over geological time, and three unknowns --- the system is indeterminate.

Or, in other words, we won't know we've been living through the sixth mass extinction until (a few million years) afterwards. At that future time, it will become obvious there's been a mass extinction.

But, do you consider there have been five earlier mass extinctions? (more?) If so, what was it that lead you to that conclusion?

 

[Bystander]

Paleontological evidence "suggests" extinction events --- alternative explanations have been proposed. What do I find more credible about the idea of abrupt mass extinctions (impactors) than pandemic "creeping crud," or deep freezes, or Siberian or Deccan Traps? Very few extraordinary circumstances and events have to be invoked to explain abrupt changes in globalfloral and faunal distributions in the fossil record.

Parsimony.

 

[Nereid]

Originally posted by Bystander
Paleontological evidence "suggests" extinction events --- alternative explanations have been proposed. What do I find more credible about the idea of abrupt mass extinctions (impactors) than pandemic "creeping crud," or deep freezes, or Siberian or Deccan Traps? Very few extraordinary circumstances and events have to be invoked to explain abrupt changes in globalfloral and faunal distributions in the fossil record.

Parsimony.

A paraphrase: if the cause seems credible, the evidence can be accepted? If not, then the evidence isn't credible??

'abrupt' =~+/- 1 million years?
'global' = >10 sites separated by >1,000 km at the time?
'floral change' = ~>3 Divisions lose >~30% of their Families?
'faunal change' =~>3 Phyla lose >~30% of their Families?

Let's have some numbers please!

 

[Bystander]

Originally posted by Nereid
A paraphrase: if the cause seems credible, the evidence can be accepted? If not, then the evidence isn't credible??

Did I fall off the turnip truck yesterday? Evidence is "credible" regardless; the hand-waving one chooses to use to explain the evidence can be credible, incredible, supported by the evidence, or not supported by the evidence, depending on the gullibility of the audience.

'abrupt' =~+/- 1 million years?

Oh, hell, let's play catastrophist --- I gave you 1Ma earlier, but you want to ask a second time --- let's say it's all over but the shouting in a day, and let the shouting last 30 yrs. for last survivors.

The stratigraphic record doesn't really have a resolution less than 1 Ma --- as a result, the paleo types fall into catastrophist and gradualist schools, and without discovery of mixed ground fish, dinos, and shrubbery in TX or SA turbidites, that argument is never going to be resolved.

'global' = >10 sites separated by >1,000 km at the time?

Tain't likely all the big 5(6) stand up to this test --- evident in all known outcrops of specified age suit you?

'floral change' = ~>3 Divisions lose >~30% of their Families?
'faunal change' =~>3 Phyla lose >~30% of their Families?

OK last time we went through this part.

Let's have some numbers please!

That's the point: we are talking about THREE numbers, appearance rate, extinction rate, and the difference between the two. We can determine an AVERAGE value for the difference over geological time. We CANNOT determine an instantaneous value for historical cases, or for the present. We have no values for appearance or extinction rates historically or for real time. There are ESTIMATES of an extinction rate based on a mix of "specialist" and other type species. If we agree to delete the "specialist" species from the rate estimate, there is still NO basis for concluding anything, because we lack information on the appearance rate, the historical extinction rate, and on the variation of appearance and extinction rates.

I can't state it any more clearly, "There is insufficient information available to conclude a damned thing."

 

[Bystander]

Sole', et al, Nature, vol. 388, 21 Aug., 1997, pp. 764-6.

Might as well get the third horse into this race. Everyone in the "chaos crowd" should like this.

 

[Nereid]

Originally posted by Bystander
Sole', et al, Nature, vol. 388, 21 Aug., 1997, pp. 764-6.

Might as well get the third horse into this race. Everyone in the "chaos crowd" should like this.

I'm pretty sure http://pangea.stanford.edu/Oceans/GES290/SOC/GES290sole1997.pdf is the paper you're referring to.

Nereid: "But, do you consider there have been five earlier mass extinctions? (more?) If so, what was it that lead you to that conclusion?"

Bystander: "Paleontological evidence "suggests" extinction events --- alternative explanations have been proposed. What do I find more credible about the idea of abrupt mass extinctions (impactors) than pandemic "creeping crud," or deep freezes, or Siberian or Deccan Traps? Very few extraordinary circumstances and events have to be invoked to explain abrupt changes in globalfloral and faunal distributions in the fossil record.

Parsimony."

Sorry, I really am in the slow class today, ... your POV is that we can't really discuss a purported sixth mass extinction, because we haven't yet agreed that there've been five mass extinctions (or four, or three, or even one)?

(this is quite separate from any consideration as to whether there is, or could be, sufficient info "to conclude a damn thing")

 

[Bystander]

Originally posted by Nereid
I'm pretty sure http://pangea.stanford.edu/Oceans/GES290/SOC/GES290sole1997.pdf is the paper you're referring to.

Yup.

Sorry, I really am in the slow class today, ... your POV is that we can't really discuss a purported sixth mass extinction, because we haven't yet agreed that there've been five mass extinctions (or four, or three, or even one)?

Nope.

POV is,"Extinction rate, estimated, calculated, divined by Madame Cleo, is meaningless outside a context of historical extinction rates." The only historical information I can see/agree to at the moment is that we can calculate/estimate an average difference in appearance and extinction rates; there is not adequate evidence to support estimates of absolute values for either.

The paper is "grist for your mill" --- you might be able to winkle out an idea of where the current extinction rate estimates fit within the power law distribution, and maybe some idea of absolute rate --- I ain't going to mess with it right now. Their remarks re. power law and the "big 5(6)" as far as them being indistinguishable from other extinctions depend on time frames (stratigraphic uncertainty being a few Ma in all cases for their purposes); more recently (no ref. at hand) the KT(?) has been pinned to something like 100ka for an outcrop in China --- might actually throw that one outside the fit.

Fair 'nuff?