Ghost Mountains and Vanished Oceans

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Science P*rn.

My interest in “gosh-wow!” science has recently been sparked by deep-time geology. The idea of vast mountain ranges over New York city that have been weathered away by rain and gravity leaves me with an existential itch to shovel more facts into my mind so that my imagination can run wild with the thoughts of things I will never see.

This book is a delightful way to scratch that itch. The author, John Wilson, is a Canadian geologist, and this book is mostly about the Lithoprobe project, which put together a map of how the Canadian part of North America was assembled from proto-continents and tectonic accretions. The author is a good prose writer who has a gift for explaining his subject and making it interesting. An added fillip is that he intersperses his chapters with a chapter written by a guest geologist about some memorable event that happened to them on a geological expedition, most of which have to do with bear attacks or natural disasters. Those chapters advance the romance of geology in a nice way.

Wilson's survey starts with the distant, distant past. One of Wilson's very nice descriptions is his way of conceptualizing deep time. After all, can our mind conceive of a million years? How about a billion years? His approach is to use the doubling of a grain of rice for each square of a chess board. In a very few squares - 20 to 30 - you are sending out for billions of rice grains, amounting to the geological times he is speaking about.

And what an imagination-sparking time those were. For example:

“Our early Earth was hammered by levels of meteorite bombardment that would quickly wipe us all out today; the rates that Palissy and Hutton's grains of sand washed off mountain tops used to be much more dramatic when there was no land vegetation to hold the sediments in place; the ice caps of the last ice age melted and vast floods of melt water carved valleys across the continents. Two billion years ago on any of the continents, nothing walked, swam or flew around, there was no grass or leaves for a cool breeze to blow through, and that breeze was mostly the movement of air made of carbon dioxide, carbon monoxide, sulphur dioxide, chorine, nitrogen, helium, ammonia and methane, but radical change was in that poisonous air. A holocaust was happening in the oceans.

The time around two billion years ago was in the Paleoproterozoic (for the perfectionist, the Rhyacian and Orosirian). Prior to then, in the Neoarchaean, life was dominated by creatures that did not require oxygen to live. This was sensible, as, for most of that time, there was about as much free oxygen on Earth as there is today on Jupiter's sixth moon, Europa; that is, at sea level, enough to fill about half a dozen covered football stadia.

As a consequence, the iron parts of a time machine wouldn't rust, although, given the harsh atmosphere, they would probably corrode in other ways pretty quickly. Iron in the ocean was precipitated in layers on the sea floor, but as sulphides rather than oxides. Then all that changed when, geologically speaking, the oxygen content of the atmosphere shot up. Things began to rust as iron found an element with which it would like to combine. Suddenly, there were no more layers of iron sulphides on the ocean floor, but rusty-red sediments on the land. We owe this extraordinary step forward to one the lowliest of creatures.”

So, that was the Earth a “mere” two billion years ago, as alien a planet as we could conceive.

Wilson's story is about the assembling of North America and we are offered approximately three super-continents, when all the continents were jammed together, and a time when the American mid-west was an ocean. Wilson provides an explanation for the famous New Madrid earthquake that shook Missouri in 1811. If you don't know about that earthquak, you should:

“Generally, if you live away from an active continental margin, you don't need earthquake insurance. However, there are exceptions. In the eight weeks between December 16, 1811 and February 11, 1812, the small frontier town of New Madrid and other communities along the Mississippi River were rocked by no less than sixteen major earthquakes. The three most dramatic quakes measured close to eight on the Richter scale and rank as some of the strongest earthquakes in recorded history. Trees were thrown around, water spouts shot up ten feet into the air, and the Mississippi River was diverted. If it happened today, with the increased modern population, it would be a natural disaster on an almost unprecedented scale.”

So, why was there such an event in a place which ought to be earthquake free? Johnson explains:

“Major earthquakes are relatively common where plates come together, for example, along the west coast of North America, the Himalayas and Indonesia, but New Madrid lies in Kansas, near the border with Tennessee. It's supposed to be stable, thick, continental crust, but it wasn't always so. Around five hundred million years ago an ocean, Iapetus, opened to the south and east of New Madrid. For a while, it was a respectable ocean, several thousand kilometres across and, of course, it began with rifting and a triple junction. Iapetus is long gone, but the failed arm, the Reetfoot Rift system, runs along the Mississippi River beneath New Madrid.”

And, then, there is the tale of the eels:

“Eels are slimy and difficult to skin (the best way is to nail their head to a post or tree, slit around just below the gills with a very sharp knife, and peel the skin off like a glove), but their flesh tastes wonderful when lightly fried in olive oil with garlic. They also have very odd mating habits.

Atlantic eels fall into two species: the North American eel (Anguilla rostrata) and the European eel (Anguilla anguilla). Each species lives in the rivers and estuaries of its appropriate continent, but both return to the Sargasso Sea to breed.

The Sargasso Sea may have been mentioned by the fourth century poet Rufus Festus Avienus, and is the only sea in the world without a shore. It is a huge area of the Atlantic Ocean (1,100 km wide by 3,200 km long) of warm, seaweed-clogged water lying between the Azores and the West Indies, and latitudes 20 and 35 north. These are known as the “horse latitudes” because so many of the Spanish and Portuguese ships sailing through them found themselves becalmed and had to throw their horses overboard to conserve water. The surface of the sea is covered with sargassum seaweed and the area has an evil reputation as the graveyard of ships. However, at certain times of the year, the waters below the surface host a writhing, joyful copulation of eels.

The mystery of the Sargasso Sea eels is in trying to explain how two very similar species can breed in the same place and yet unfailingly divide into two distinct populations that undertake very different journeys to opposite locations to live out their lives as adults.

The North American eels have by far the easier time of it. Their journey back to the eastern seaboard is short, although it takes the young glass eels a year to make it. Tough though that journey is, however, it is nothing compared to the odyssey of the European glass eel that faces a two- to three-year, almost six-thousand-kilometre journey back across the Atlantic.

Two different populations of eels, breeding in the same place, but undertaking vastly different journeys back home. Clearly, something has happened since the Atlantic eels' ancestors squeezed through the closing gap between North and South America some fifty million years ago. Perhaps the ancestral eels once faced a similar trek regardless of whether they headed east or west out of the Sargasso Sea. Perhaps the ancestral Hudson and Severn Rivers were equally accessible. Unfortunately, at least for Anguilla anguilla, eels never developed the science of geology. Unbeknownst to the eels, as the eel offspring wriggled and drifted their way homeward, things were going on far beneath them. The Atlantic Ocean got wider, and each year the eastward-headed eels had a centimetre or two more to travel. For countless generations it made no difference. However, eventually, the changing distances meant that the two populations were arriving to breed at slightly different times. Given enough time, two separate species arose, one blithely continuing its age-old journey totally unaware that its close cousins were struggling with an ever-more-daunting migration.”

Plate tectonics causing speciation? Wilson says that this hasn't been proven, but how interesting if true.

This is a fun book to dip your toes into the water of deep time.