Without Plate Tectonics There Is No Life: Earth Is the Lucky Planet
Plate tectonics remakes the Earth's surface at the speed a fingernail grows, creating and destroying roughly 3 square kilometres of ocean crust every year. It shifts climate, isolates species, and even determines whether life exists at all — without it, there is none.
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The argument · tap a timestamp to hear it
Plate tectonics was not a sudden insight of the 1960s
Richard traces the prehistory of the idea. In the 16th century the Dutch cartographer Abraham Ortelius already noticed how the west coast of Africa fits South America; Bacon and Franklin both took an interest. But it was not until the early 20th century that the German Alfred Wegener genuinely proposed that the continents had once been joined in a single supercontinent and had moved. Richard stresses that plate tectonics is a package of three things: continental drift, seafloor spreading, and the synthesis that explains both. He describes it as geology's oak king in the forest — without it the whole discipline loses its unifying framework. The point of this build-up: the revolution did not appear out of nowhere in the 1960s, it was an intuition suppressed for nearly three hundred years.
— Richard CorfieldSeafloor spreading was a postwar dividend of anti-submarine equipment
Joe tells a fascinating stretch of scientific history. Arthur Holmes was the first to imagine mid-ocean ridges splitting apart and the seafloor being carried along on deep mantle flow, but it stayed theory. Harry Hess was a naval captain in the Second World War, accumulated measurements while sailing the Pacific, and after the war became an extraordinarily persuasive advocate. The war itself contributed more: magnetometers, sonar and explosives — the anti-submarine toolkit — were in surplus afterwards, and together with ship time and scientific staff who knew how to operate them, all of it was thrown at ocean exploration. People immediately found that the mid-ocean ridges run right around the globe, that there is a rift valley down the middle, that earthquake belts accompany them, and that the magnetic anomaly signals were abnormally large. The seafloor was no longer a silent plain but an archive holding the evidence.
— Joe CannMagnetic stripes turned a happy idea into science you could calculate
Joe remembers this as someone who lived through it: as an undergraduate who started in 1967, what he was taught was still the old framework of things like geosynclines, with no unifying principle. Then Fred Vine and Drummond Matthews proposed that if the seafloor spreading hypothesis held, and if the geomagnetic field reverses periodically, then symmetrical magnetic stripes should form on either side of a mid-ocean ridge — and the spreading rate could be calculated from them. They actually found them. Add the map of the mid-ocean ridges that Bruce Heezen and Marie Tharp drew with sonar, plus the recycling by subduction that Hess supplied from gravity data, and plate tectonics went from a ‘happy idea’ to quantifiable science. Joe says it was like a scrambled jigsaw suddenly falling completely into place.
— Joe CannContinents rearrange land and sea at the speed a fingernail grows
Joe describes the concrete mechanism of plate motion. The plates slide on the asthenosphere at a depth of about 100 kilometres, a layer containing a small amount of melt that acts as a lubricant. Each year about 3 square kilometres of new ocean crust is created at the mid-ocean ridges, and the same area is destroyed at subduction zones, so the Earth stays the same size. Plates move at roughly the speed at which fingernails or hair grow. Continental crust is thick and light and cannot sink to be recycled; it only crumples in collisions into complex mountain ranges like the Himalaya. Ocean crust is dense and subducts back into the mantle. It is precisely this slow, centimetre-scale motion that has reshaped the distribution of land and sea over hundreds of millions of years.
— Joe CannPlates are the underlying switch in Earth's climate system
Richard points out that plate reorganisation does not merely change the positions of land and sea — it changes global climate through ocean currents. He gives the Benguela current as an example: once the South Atlantic had widened enough, this cold current running north along the coast from Antarctica switched on abruptly, pushing cold northwards and completely changing the climatic pattern of Africa. Joe adds another case: about 30 million years ago Australia and then South America separated from Antarctica, forming the circum-Antarctic current system, which allowed the Antarctic ice sheet and the strong southern-hemisphere wind belts to take shape. This shows plate tectonics is far more than geology. It is the real underlying switch in Earth's climate system — change the arrangement of land and sea and the currents, the atmosphere and the ice sheets all reset with it.
— Richard CorfieldLife may have originated at black smokers, where no light reaches
Richard describes a connection that is usually overlooked. In the 1970s humans descended to a mid-ocean ridge for the first time and found communities of organisms living there that do not depend on photosynthesis but survive by chemosynthesis. Black smokers vent mineral-rich black water and support an entirely new ecosystem; some people even hold that life originated there. He also cites Australia's marsupials: plate motion separated the continent, and in that isolation the marsupials independently evolved into ecological niches parallel to those of the placental mammals of the northern hemisphere. Plate tectonics therefore does not only shape geology — by cutting continents apart and isolating populations, it takes a direct part in the story of the evolution of life.
— Richard CorfieldMars stopped, Venus never started, and Earth is the lucky one
The programme ends with a superb argument. Richard says bluntly that extreme Gaian positions like ‘the Earth is alive’ and ‘humans are a collection of microbes’ are absurd; Joe retorts that he sounds like the people who rejected continental drift in 1928. Lynn takes a middle position: microbial symbiosis got multicellular life started, but the distribution and survival capacity of microbes was initially determined by plate tectonics. Joe holds firm that without plate tectonics there is no life, because water seeping into the mantle softened it so that the plates could slide at all — and because life itself originated in the chemical energy of submarine hydrothermal systems. He then pulls the scale out to the planetary: Mars may have had plate tectonics but it stopped long ago, Venus never had any, only volcanoes, so Earth is the lucky one. This stretch turns the whole theory into a judgement about planetary habitability.
— Joe CannIn their own words · checked verbatim
It's really the Royal oak of geology. It's the tree that dominates the forest and without which none of the science really makes sense.
Richard Corfield5:54
in 1928, the Americans had a meeting where they declared continental drift as impossible and so you couldn't teach continental drift in American universities at all after then
Joe Cann10:23
The oldest ocean crust is only 180 million years old.
Richard Corfield16:08
About as fast as your fingernails grow.
Joe Cann22:57
The San Andreas fault is constantly moving.
A long time to a geologist is not the same thing as a long time.To everybody else.
Life wouldn't exist without plate tectonics.
Joe Cann43:54
on Venus. There is no plate tectonics. There is only volcanism.
Joe Cann45:00
Figures
| Oldest age of ocean crust | 180 million years | 16:08 |
| Area of ocean crust created and destroyed each year | about 3 square kilometres | 22:57 |
| Dip of subduction-zone earthquakes | 40 to 60 degrees | 26:16 |
| Projected disappearance of the Mediterranean | 150 million years from now | 21:49 |
| Formation of the circum-Antarctic current | about 30 million years ago | 31:44 |
Glossary
- Benioff zone
- The inclined band along which earthquake foci are arranged within a subduction zone, dipping at about 40 to 60 degrees.
- seafloor spreading
- The process by which new ocean crust forms at mid-ocean ridges and spreads outwards.
- Vine–Matthews hypothesis
- The hypothesis that symmetrical magnetic stripes on either side of a ridge demonstrate seafloor spreading and geomagnetic reversal.
- mantle plume
- A column of hot material upwelling from the deep mantle, capable of forming chains of volcanic islands.
- black smoker
- A hydrothermal vent at a mid-ocean ridge that emits black, mineral-rich fluid and supports chemosynthetic life.
- Gaia theory
- The hypothesis that the biosphere and the inorganic environment jointly regulate the state of the Earth.
How to listen
Founders, engineers and investors who want to understand Earth systems, the origin of life and planetary habitability — especially anyone making calls on climate, deep space or resources.