History › Complex life › Life's move onto land
Carboniferous coal forests
c. 359–299 million years ago· Event· Universe & Earth
Well documentedSolid records, physical evidence or scientific consensus.
Vast swamp forests of giant club mosses and tree ferns grew, died and were buried, becoming much of the world's coal.
See it on the History map →What happened
During the Carboniferous Period (the name means 'coal-bearing'), wetlands covered much of today's North America and Europe. Dead plants piled up in waterlogged swamps where they could not fully rot, became peat, and over millions of years of heat and pressure turned to coal. Oxygen may have reached about 30 percent, versus 21 percent today, letting insects grow huge: dragonfly-like insects spanned about 70 cm (over 2 feet).
Why it matters
This coal powered the Industrial Revolution some 300 million years later (see Steam engine and Industrial Revolution), and burning it drives today's climate change.
How we know
Coal seams full of fossil bark, leaves and spores; fossil giant insects such as Meganeura from France; chemical records of ancient oxygen levels.
Still debated
Why so much plant matter escaped rotting is debated: an older idea says wood-eating fungi had not yet evolved; newer studies point to wet climate and sinking basins.
Connections (3)
▸Life's move onto land led to the Carboniferous coal forestsMostly agreed
The connection
Once plants evolved roots and wood, they could grow into tall trees. By the Carboniferous, giant club mosses and tree ferns formed vast swamp forests. When these plants died in waterlogged ground, they were buried before fully rotting and slowly turned into the coal mined today.
When and how
In tropical swamps of what are now North America, Europe and China, about 359–299 million years ago.
How sure are we?
Coal seams contain fossil bark, leaves and spores; repeating layers of coal and rock match known cycles of rising and falling sea level.
Debates and open questions
Whether Carboniferous conditions were unique, or such coal could form at any time given wet, sinking basins, is debated.
▸Carboniferous coal forests laid down the coal that fueled Industrial RevolutionWell documented
The connection
Plants in Carboniferous swamps, about 359 to 299 million years ago, were buried before they fully rotted and slowly turned into coal. Britain sat on rich, shallow seams of it. That cheap, dense energy ran the steam engines, ironworks and railways of the Industrial Revolution, replacing wood and muscle. The Curious Science and Life maps cover how coal formed.
When and how
Coal formed in swamp forests 359 to 299 million years ago; it was mined on a massive scale in Britain from the 1700s, then in Belgium, Germany and the US.
How we know
Fossil plants in coal seams show its origin; British coal output rose roughly tenfold between 1700 and 1830.
Debates and open questions
Why so much coal formed then is debated. One idea is that fungi could not yet break down wood's tough lignin; recent studies doubt it.
▸Steam engine burned fuel from Carboniferous coal forestsWell documented
The connection
Steam engines burned coal, much of it formed from Carboniferous swamp forests some 300 million years ago. The first engines were built to pump water out of coal mines, so coal powered the machines that dug out more coal. In effect, industry began spending a vast store of ancient sunlight.
When and how
Newcomen's first known engine pumped a coal mine near Dudley, England, in 1712; most British coal seams date from the Carboniferous period.
How we know
Mine records and surviving engines; geology and fossil plants show most British and Appalachian coal is Carboniferous in age.
Debates and open questions
Much of the world's coal, such as the vast Powder River beds of Wyoming, formed later; why the Carboniferous left so much is still debated.