Who will be remembering
you 199 years from now? As a non-breeding member of the human population, I can pretty much guarantee there won't be any of my genetic heirs flying around in their jet-packs or tooling about in superconductivity hover-cars while reminising dear old, great, great, great, great grand MacDaddy. Alas. But here we are, just shy of 200 years, and the world celebrates the memory of Charles Darwin on Tuesday, February 12. I'll certainly be raising a glass to the much revered, brilliant hypochondriac a few times through the day (give me a ring or shoot me an email if you want to virtually toast the man with me).
The prolific Jennifer Jacquet over at
Shifting Baselines has already done a magnificent round-up of Darwin's fascination with, and interest in, many things marine. In fact, while he was the quintessence of the Victorian naturalist gentleman, I will still always regard him as one of the few, the proud, the marine biologists. Just a peek at Jennifer's tally is enough to secure his more than honorary membership. Darwin's output, without even considering his magnum opus with the
Origin, was staggering. If I manage to grind out the tiniest percentage of Darwin's combined contribution to my field of marine science I'd be astonishingly lucky. Crude as it may sound, we are all Darwin's bitches.
In the early portion of his five-year voyage aboard the
HMS Beagle, Darwin had deduced an explanation of the geological processes that created coral reefs by applying
Charles Lyell's explanations of uplift and subsidence. He argued that the Chilean coast had been rising while the ocean floor was subsiding (sinking). When he finally explored some barrier reefs during the voyage, he knew that since the reef-building coral polyps could not live deeper than about 120 feet, and all the coral below that depth was dead, the confirmation of the reefs' great depth was evidence of subsidence.
In his 1842 work,
The Structure and Distribution of Coral Reefs (title page image at top of this post), Darwin formulated his explanation for the formation of coral atolls in the South Pacific which involved considering that several tropical island types—from high volcanic island, through barrier reef island, to atoll—represented a sequence of gradual subsidence of what started as an oceanic volcano. He reasoned that a fringing coral reef surrounding a volcanic island in the tropical sea will grow upwards as the island subsides, becoming an "almost atoll" (barrier reef island) (as typified by an island such as
Aitutaki,
Bora Bora and others in the Society Islands). In time, subsidence carries the old volcano below the ocean surface, but the barrier reef remains. At this point, the island has become an atoll.
Darwin's subsidence model was grounded in Lyell's geologic principle of
uniformitarianism. Big word, simple concept. In brief, it explains that the present is the key to the past. In other words, geological processes taking place today (weathering, landslides, earthquakes, etc.) operated last week, last month, last decade, and so on. Inspired by his firsthand observation of an earthquake in South America and his deduction that the Andes mountains are still rising, and the nearby seafloor, sinking, Darwin imagined a balance between reef expansion and island subsidence.
In an interesting fragment of his autobiography, Darwin gives us a very clear account of the way in which the leading idea for his theory of coral-reefs originated in his mind; he writes, "
No other work of mine was begun in so deductive a spirit as this, for the whole theory was thought out on the west coast of South America, before I had seen a true coral-reef. I had therefore only to verify and extend my views by a careful examination of living reefs. But it should be observed that I had during the two previous years been incessantly attending to the effects on the shores of South America of the intermittent elevation of the land, together with the denudation and deposition of sediment. This necessarily led me to reflect much on the effects of subsidence, and it was easy to replace in imagination the continued deposition of sediment by the upward growth of corals. To do this was to form my theory of the formation of barrier-reefs and atolls."
Many delays from ill-health made the completion of
The Structure and Distribution of Coral Reefs a more protracted process than usual. Not that any of Darwin's works was a straightforward process. The task of elaborating and writing out his books was always a very slow and laborious one; but it is clear that
Coral Reefs was a long and constant struggle with the lethargy and weakness resulting from the sad condition of his health at that time. (It's almost painful to dwell on some of the Victorian quackery Darwin subjected himself to during his bouts of illness, psychological or otherwise.) Darwin writes in his autobiography, "This book, though a small one, cost me twenty months of hard work, as I had to read every work on the islands of the Pacific, and to consult many charts."
Darwin sweated the details even after publication. One of his letters to Lyell post publication is particularly representative of his hand wringing. The accumulation of such impressive and complex reef formations in the South Pacific surprised even Darwin. Enough so that he wrote Lyell several times (almost) second guessing himself:
Considering the depth of ocean, I was, before I got your letter, inclined vehemently to dispute the vast amount of subsidence, but I must strike my colours,— with respect to coral-reefs I carefully guarded against its being supposed that a continent was indicated by the groups of atolls. It is difficult to guess, as it seems to me, the amount of subsidence indicated by coral-reefs; but in such large areas, as the Low Arch: the Marshall Arch. and Laccadive group, it would, judging from the heights of existing oceanic archipelagoes, be odd if some peaks of from 8000 to 10,000 had not been buried.
Letter: Darwin to Lyell, 25 June [1856]
As powerful an explanatory mechanism as subsidence was, it had it's problems in some ocean basins. In certain specified cases--Palau (known during Darwin's time as the Pelew Islands) and Bermuda--subsidence could not have played the main role in originating the peculiar forms of these coral islands. But Darwin and his supporters maintained that these were exceptional cases and were not sufficient to invalidate his theory of subsidence as applied to the widely spread atolls, encircling reefs, and barrier-reefs of the Pacific and Indian Oceans. Keep in mind that none of Darwin's coral reef hypotheses ever benefitted from the concept of
plate tectonics. Many of the associated "problems" which subsidence alone could not explain would later disappear with the mechanisms of subduction, strike-slips, folding, transform faults, and more.
In fact, in an 1881 letter to Alexander Agassiz, Darwin demonstrated his characteristic humility while still clinging to subsidence as a theory for deep oceanic processes,
If I am wrong, the sooner I am knocked on the head and annihilated so much the better. It still seems to me a marvellous thing that there should not have been much, and long-continued, subsidence in the beds of the great oceans. I wish some doubly rich millionaire would take it into his head to have borings made in some of the Pacific and Indian atolls, and bring home cores for slicing from a depth of 500 or 600 feet.
See
Deep Sea News, guys. You're living out Chuck's dream!
Happy
Darwin Day and see you for the bicentennial! Woot!
I'll be the first to admit that I lack the huevos to try this myself, but Kona appears to be at the cutting edge of a new extreme diving experience: Black Water Diving. How does it work? After dark, your boat takes you into deep Pacific water. You tether yourself to the boat, drop overboard with small lights, and sink to about 60 feet. Then, if you really want to feel like part of the planktonic community, you turn your lights off and just drift. Excuse me as I pause here to let the goosebumps settle.
