[Coral-List] Geologists and deep time
riskmj at mcmaster.ca
Fri Sep 20 11:14:28 EDT 2013
A number of recent postings to this List have seemed to me to be examples of the sort of “gotcha” comment that characterizes our Twitterverse. They serve largely to remind us that, nowadays, any moron with a mouse can make mischief. These postings are also a reminder that it is always better to do your homework BEFORE you post, rather than AFTER.
I would like to elevate the conversation, following the excellent suggestion of Iain Macdonald to “stick to science.” I apologise in advance for clogging the mailboxes of those of the SEVEN THOUSAND SEVEN HUNDRED subscribers to this list (I stand happily corrected by Jim) who would not be interested.
This thread began, as so many do, with Gene Shinn and his admonition to listen to the geologists. In an ideal world, this should not be necessary, but bitter experience has taught me never to underestimate underachievers. So I will outline only one aspect of the value in consulting with our geo-colleagues (my PhD is in Biology.) The alert reader will discern several themes in the following.
Iain, a man whose ethnic origins seem clear, conjures up the shade of James Hutton, a Scot who taught us all to observe processes and predict/postdict their results. Hutton taught Lyell, another Scot, who went on to be the first Professor of Geology at Cambridge. Darwin, an Englishman (you can’t win them all) dropped out of Univ. of Edinburgh, and went to Cambridge. The only textbook he took on the voyage of the Beagle was Lyell’s Principles of Geology.
So we need to be clear on the fact that Darwin was a paleontologist: all of us who believe in evolution are listening to geologists.
There is another aspect of current reef-think that could benefit from reference to the geologic record. There is a great deal of talk to-day about reef resilience, adaptation, etc-as though by choosing the right strains of zoox, or selecting hardy coral clones, we can somehow re-create reef simulacra some time in the future. Personally, I prefer trying to preserve the reefs we have now, rather than rely on uncertain science for an uncertain future. And the geologic record speaks volumes-for those who can read-about responses to climate change.
The great reef tracts of the past were all slain by some aspect of climate change. None of them experienced impacts of overfishing or OA, although nutrient increases were implicated in some extinction events.
The majestic Devonian reefs of western Canada and the Canning Basin, in Australia, were extinguished in a late-Devonian event that, strangely enough, has been linked to global cooling. The idea is that the rise of land plants, with increased carbon storage and rock weathering (think: roots) locked up so much atmospheric CO2 that the subsequent cooling knocked off the corals. Reef-building never really got going again until the Permian.
By the way, a recurring theme here is oil exploration. Both the Canning Basin and Alberta reefs contain large amounts of hydrocarbon reserves, which drove a lot of good reef research. In addition, the Tar Sands oil in northern Alberta (the exploitation of which, by the way, is opposed by many of us) is Devonian reef oil that migrated up-dip and became oxidized to bitumen in estuarine sand bodies.
Historically, geologic research has often been driven by industry-oil, mining-whereas the major patron of biological research has been government. This has led to a fundamental difference in hard-wiring: for example, biologists favour analysis of variance, which mostly tells you that one of these things is not like the other, whereas geologists much prefer regression analysis, which tells you it’s over there.
But I digress, again.
After the Devonian extinction, there was a large hiatus-100 million years, give or take-before the taxonomically-complex reefs of the Permian. Think, West Texas oil. These reefs also vanished, in the largest mass extinction the globe has seen. So far.
Reasons for this extinction are still being debated. A drop in sea level due to a slowdown in sea-floor spreading would have exposed the shelves. Or, current thinking involves large volcanic events which changed the chemistry of the oceans. Either way-a huge extinction event, followed by a long hiatus before reefs get going again.
Scleractinians arose in the Mid-Triassic, say 20 million years after the terminal Permian event, but it took a while before they amounted to much. The supposed bolide event at the K/T boundary put a stop to reef development for a while.
Roughly 40 million years later, reefs had developed in the Oligocene. These all vanished in the Oligocene-Miocene extinction event, which seems to have been triggered by nutrient increase (Edinger and Risk, 1994).
The final example would be recolonisation of the shelves during the Holocene. This does not count as recovery after an extinction event, because the corals were still there, but hunkered down offshore. Nonetheless, in a series of elegant papers, Walter Adey has shown that it took at least 1,000 years, AFTER sea level reached its present height, before corals could re-establish. It took that long to work out all the fines, produce the hardgrounds, yadda yadda.
So the pattern here is that it has taken many millions of years for reefs to recover from mass extinction events. To suggest that we can somehow overcome this, in the face of all the other problems that will be facing the species, would be the height of hubris.
Ulf's argument that we cannot conclude anything because "it would require complete preservation of the geological archive" is one of the favourites of creationists-and that is all the response it deserves.
The bad news does not end there. A series of papers by now 30 years old (e.g., Kobluk, Pemberton and James 1977, Science v. 197) describes the behaviour of the bioeroding fauna passing across a mass extinction timeline. The corals die-like flies. The bioeroders hide in hardgrounds, waiting for the next skeletal organism to arise so they can jump all over them. (This is, by the way, the reason aspects of the bioeroding fauna are circumglobal. They predate the corals they invade.)
So hopes that we can somehow reinvent reefs are built on shaky ground. The Holocene took 1,000 years, and that was when the seas were clean. The newly-rising oceans will have to rework all the condos along Miami Beach and get rid of the excess nutrients from decomposing voters before they could possibly re-establish. And when they try-like death and taxes, Cliona cannot be avoided.
In short, the more we listen to geology the harder we should try to preserve what we have.
Mike Risk (whose ancestors came to the New World from Glasgow in 1812 and took up farming 30 miles from where we now live.)
On 2013-09-20, at 7:56 AM, Ulf Erlingsson wrote:
> The conclusion expressed below cannot be supported by science, since it would require complete preservation of the geological archive, which is never possible. In laymen's terms, the absence of proof is not proof of absence.
> On 2013-09-19, at 11:53, Michael Risk wrote:
>> Had you asked me, I would have said: reefs have died like flies from climate change all through the Phanerozoic. The MOST RAPID recolonisation was the 1,000 years it took reefs to reoccupy the shelves during the Holocene Transgression. Usually, they vanish for 10's of millions of years.
riskmj at mcmaster.ca
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