Darwin on Atolls

Charles Darwin inferred nearly 200 years ago that seamounts (submarine volcanoes) 100 meters or so below present sea level were islands during the ice ages when a vast amount of water was sequestered as ice in the continental glaciers of the northern hemisphere. The coral reefs surrounding those ancient islands were able to grow fast enough to remain at or near the sea surface as the sea level rose gradually during the melting of the ice. This surmise nicely accounts for the atolls and their lagoons that persist.

I read Darwin’s Origin of Species in 1938 and have been eagerly awaiting confirmation of his suggestion about the origin of atolls. Obviously this can be done by drilling 100 meters into these coral structures to reveal the underlying volcanic rocks. In recent decades several such holes have been drilled obtaining volcanic rocks in each instance.

The Origin of Species is the only ground-breaking scientific treatise ever written for the general public. Its entire first printing of 500,000 copies was sold in a few months. I was privileged to stumble on it as my “personal” textbook of biology at age 14 three years before taking an academic biology course. In preparation for writing this brief article, I searched The Origin of Species where the origin of atolls was explained. I was amazed to find only the following brief mention as part of a discussion of such temporary islands that may have been used as “halting places” during migrations of plants and animals across oceans en route to establishing life on newly formed islands for example, Hawaii. Here is the entire quotation exactly as Darwin wrote it:

“… I frankly admit the former existence of many islands, now buried under the sea, which may have served as halting places for plants and for many animals during their migration. In the coral producing oceans such sunken islands are now marked, as I believe, by rings of coral or atolls standing over them……”

Summary: Darwin’s book has provided me with many insights for understanding our world and even its many small details are interesting—how else could I have remembered his brief, casual mention of how atolls arise? My source of Darwin’s book for the quotation was The Cook Islands Library and Museum in Avarua. I have written more about evolutionary biology which is available on www.frantzmd.info Look in the website under the category Other Science and Technology for the article entitled “An open Letter to the Surgeon General (evolutionary biology)”.

John A. Frantz, Global Volunteer, The Cook Islands, November 25, 2006