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Polymetalic Nodules Are Weird

May 13, 2026

AI Summary

5 min read

"These rocks have the most unreal history, present, and future."

That is how Hannah Fry introduces the polymetallic nodule she has brought to the studio — a black, chalky rock the size of a die, sent to her Cambridge office by an anonymous donor. The rock is unremarkable to look at but contains a story that spans the age of dinosaurs, a Cold War CIA heist, and the paradox of green technology. Michael Stevens licks it anyway, because he is Michael Stevens.

How the ocean grows a battery

Polymetallic nodules form through a process called hydrogenous precipitation. It begins with a tiny seed — a shark tooth, a fragment of a meteorite, or even a megalodon tooth — that settles into the mud at the bottom of the ocean. Over millions of years, underwater volcanoes spew metallic debris across the seafloor, and dissolved metals like manganese, nickel, and cobalt slowly come out of the seawater and bond to that original seed. The accumulation rate is almost incomprehensibly slow: about one millimeter every million years. By the time a nodule reaches the size of a potato or a grapefruit, the seed at its center may date back to the time of the dinosaurs.

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What you'll learn

  • 1 (00:00) **Introduction & The Howard Hughes Cover Story** - Hannah introduces a field notes episode with a mysterious object, starting with the story of Howard Hughes and the Glomar Explorer.
  • 2 (03:54) **Polymetallic Nodule Reveal & Physical Description** - Hannah presents the actual object: a polymetallic nodule from the Atlantic Ocean, sent to her as a gift.
  • 3 (06:20) **How Nodules Form: The Slowest Geological Process** - Hannah explains the incredible, slow creation of these rocks over millions of years.
  • 4 (08:35) **Nodules as Natural Batteries** - The nodules have a surprising electrical property due to their metallic layers.
  • 5 (09:18) **The Modern Paradox: Green Tech vs. Environmental Damage** - The metals in the nodules are exactly what is needed for green technology like electric car batteries.
  • 6 (14:32) **Listener Question: Training for Ambidexterity** - Mike asks if it's possible to train oneself to be ambidextrous.
  • 7 (16:50) **Ambidexterity, Brain Health, and Left Neglect** - Hannah wonders if training for ambidexterity could be good for staving off dementia, before diving into the strange phenomenon of left neglect.

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Show Notes

What if one of the most valuable objects on Earth has been sitting untouched at the bottom of the ocean for 100 million years?


In this Field Notes episode, Professor Hannah Fry brings Michael Stevens (VSauce) a strange metallic rock formed in the deepest parts of the Atlantic over millions of years.


What begins with a bizarre Cold War CIA cover story involving Howard Hughes and a sunken Soviet submarine quickly turns into a journey through deep sea geology, natural “electric” rocks, and the environmental dilemma of mining the ocean floor for the rare metals used in electric car batteries.


Plus: can you train yourself to become ambidextrous? are giraffes more vulnerable to lightning strikes than other animals? Does damp cold really feel colder than dry cold? And do humans actually sense wetness at all?


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