Simon says "send a smoke signal"

I am currently in the midst of some rather hectic few weeks. I seem to be flying back and forth across the Atlantic slightly more than usual. But a couple of sandwiched weeks in London thankfully coincided with my favourite author's time in the UK for the promotion of his new book. Indeed, hearing Simon Winchester speak, or reading his work, is one of (my) life's great pleasures. Every word he writes or utters seems to simultaneously educate and entertain. He truly is one of our world's great polymaths.

Simon Winchester talking about his new book, Pacific: The Ocean of the Future, at Daunt Books in London, October 2015.

His latest book—Pacific: The Ocean of the Future—is the last installment of a trilogy that also includes Atlantic: A Vast Ocean of a Million Stories and The Men who United the States. In this new offering he writes a recent biography of the Pacific, based around several major events that have shaped the largest of our oceans. He has made a conscious decision to eschew the ancient history of the Pacific, and instead focus on stories that have occurred since 1st January 1950. This date defines the present in the 'before present' (BP) timescale, which is mainly used in geology and other scientific disciplines to quantify when past events took place. Of course, it was in the 1950s that nuclear weapons testing first altered the proportion of carbon isotopes in the Earth's atmosphere and thus changed the way radiocarbon dating is conducted (read a previous postcard to learn about one proposed start of the Anthropocene at about this same time, i.e., when nuclear radionuclides became detectable around the globe).

Given that Simon was talking about one of the Earth's greatest natural features—covering about one third of our planet's surface area—I could not let the chance slip by to ask him a question. My question.  So at the end of his talk, I sought his opinion about what piece of Earth—specifically from within the Pacific Ocean—he would send into space to represent our planet to hypothetical alien planetary geologists. Obviously, I was looking for inspiration for a new postcard, but I was also genuinely interested as to what he (as a fellow Oxford geology graduate, no less!) would choose. And despite me putting him absolutely on the spot, I do believe he came up trumps with his answer (as I had no doubt he would): "Black smokers".

He thought that black smokers—rather mysterious landforms (and the exotic ecosystems they harbour) deep within the Pacific Ocean—would be a wonderful geological emissary for the hypothetical cosmic journey. I'm not sure I could have come up with a better answer.

The Sully 'black smoker' hydrothermal vent, part of the Main Endeavour Vent Field in the northeast Pacific Ocean. Credit: NOAA

These black smokers, to which Simon referred, are a specific example of underwater hydrothermal vents. Such vents are fissures in the Earth's surface from where geothermally heated water can escape. On land, hydrothermal vents give rise to features such as hot springs, fumaroles, and geysers. But in the sea, they can form black smokers. Until 1977, however, these sea vents were unknown. They were first discovered on the East Pacific Rise (a mid-oceanic ridge tectonic plate boundary) by scientists from Scripps Institution of Oceanography, who were using a deep submergence vehicle. Since then hydrothermal vents—and the associated smokers—have been found at almost all active spreading ridges (i.e., tectonic boundaries where plates move apart). Over 500 active submarine vent fields are now known.

Map of known active submarine hydrothermal vent fields. Credit: InterRidge Vents Database

The characteristic black 'smoke' that emanates from these vents is actually hot (about 350°C) liquid containing a thick suspension of dark, fine-grained particles. These metal-rich fluids are a product of reactions that take place between seawater and hot basalt, the latter of which is created at the spreading ridges. When the super-heated, metal-laden waters escape from the vents they mix with the frigid waters of the deep ocean. This abrupt mixing causes rapid precipitation of the metals and gases that were suspended in the water. Large amounts of various sulphide minerals (such as pyrite, chalcopyrite, and sphalerite), as well as silica and anhydrite (a calcium sulphate mineral) precipitate and form the chimney-like structures of the smokers themselves.

Cross-section through a black smoker 'chimney'. The concentric rings represent zones of different precipitated minerals. Credit: Rachel Haymon

But in addition to the pure geological excitement of these seafloor regions, the black smoker environments represent nutrient-rich oases in the deep ocean. As such, the areas surrounding submarine hydrothermal vents are much more biologically active than most of the dark, abyssal sea. They play host to complex ecosystems full of foreign species.

A well-developed hydrothermal vent ecosystem in the Pacific Ocean, which includes tube worms (red) and mussels (yellow shellfish). Tube worms such as these can grow to be up to
2 metres in length. They no mouth or stomach, but billions of symbiotic bacteria living inside the tube worms produce sugars from carbon dioxide, hydrogen sulphide, and oxygen.
Credit: Woods Hole Oceanographic Institution.

Because no light reaches the depths of the ocean floor (hydrothermal vents in the Atlantic and Pacific oceans exist at an average depth of 2100 metres), these species are not based around photosynthesis. Instead, these ecosystems are chemosynthetic. The alien-like species, which include varieties of clams, limpets, shrimp, and giant tube worms (specifically mentioned by Simon in his reply to my question), mostly exist by consuming the sulphide minerals that are available.

So as well as representing an exotic part of the Earth's deep sea environment, the black smokers illustrate the true variety and abundance of life that exists on Earth. To an alien planetary geologist, observing from afar, our surface biological communities are likely to be the most obvious. But without digging deeper, into our giant ocean domains, Earth's amazing diversity cannot totally be revealed. Wherever we look, our world literally teems with life.