EPISODE TWO | The Invisible World (corrected extract)

The Kidd Creek Mine in northeastern Ontario is the deepest copper-zinc mine in the world. Located twenty-three kilometres north of the city of Timmins on the traditional lands of the Mattagami First Nation, and home to the Ojibwe and Cree peoples, it is now owned by Glencore, the Swiss mining conglomerate. Descending over three kilometres is an arduous process: first you take a two-storey cage elevator big enough to hold 140 miners, then a 1.5 km battery-powered train ride, followed by another double-decker cage. Alternatively, you can take a corkscrew-shaped ramp, which at 24 km in length is one of the longest in the world. The whole journey takes almost an hour, but it was at the end of that long and winding trek that, in 2019, a team of geologists from the University of Toronto led by Professor Barbara Sherwood Lollar discovered the world’s oldest groundwater.

Professor Sherwood Lollar’s sample originally surprised her collaborators at Oxford tasked with testing its age because the result was so extreme they assumed their mass-spectrometer must be broken. It wasn’t: the reading showed the water from Kidd Creek was 1.6 billion years old. To put that in perspective, this meant it had lain untouched for a third of Earth’s lifetime. 1.6 billion years puts it in bang in the middle of the Boring Billion, when the planet was mostly covered with ocean, and the very first examples of multicellular life – thin filaments of algae – were just beginning to emerge. It was a stunning discovery, almost like finding water on Mars. But its age wasn’t the only secret that the stale and salty Kidd Creek water was hiding – it also contained living bacteria.

How could anything survive, let alone thrive down there, without light, under intense pressure and in water that is at least twice as salty as the sea? Enter stage left, sulphate-reducing bacteria like those found at the deep ocean “black smokers” – that have found a way of creating their own self-sustaining ecosystem miles under the surface.

They eat – that is, extract energy – from a mineral called pyrites, which is also known as fool’s gold because of the yellow metallic lustre of its crystals. They breathe using not oxygen, but the sulphates dissolved in the mineral-rich salt water that has dripped down from above. They then use this energy to dissolve carbon and nitrogen from the surrounding rock, full of the remains of dead bacteria which had sunk to the bottom of the ancient ocean 2.7 billion years earlier. They recycle their dead ancestors, converting them into organic compounds to balance the osmotic pressure caused by the super-salty water around them. Without this, their cell walls would explode. This ecosystem survives in a dark hot, airless world of sucking, stripping and dissolving and probably has done for billions of years.

Microbes that metabolise without oxygen are important in our story for two reasons. It is possible that the first proto-bacterial lifeforms on the planet performed the same anaerobic trick of eating rock and breathing sulphur inside the pores of alkaline oceanic vents, so they are an important clue in how life first arose; and also, because their discovery has completely revised our idea about where life can happen.

The estimate now is that instead of mostly dead rock beneath our feet as much as 20 per cent of the planet’s biomass might be formed by these subsurface microbes. This reinforces the emerging way of looking at life’s active role in shaping the planet. Some geologists now believe that these ancient bacteria with their rock dissolving skills may have been instrumental in creating the unique diversity of over 6,000 minerals we find on Earth – far more than any other planet yet explored. There is even evidence that the microbial weathering of basalt, the most common rock in the Earth’s crust, has helped accelerate the tectonic recycling of it into the granite that the continents themselves are built on. Basalt is common throughout the solar system; but granite isn’t. Could microbes have helped terraform the Earth? In a 2021 interview with Maclean’s magazine, Dr Sherwood Lollar suggested as much: We no longer think of life on Earth as this smear of biology on the surface. Life is something that deeply permeates our planet.

This story refers to sulphate-reducing bacterial ecosystems discovered at Kidd Creek. Referring to those microbes as Candidatus Frackibacter in this story was our mistake.