Life › Seas, forests & the move to land
Plants colonize land
c. 470 million years ago (spores); maybe earlier· Event· Plants & fungi
Strong evidenceGood evidence; dates or details still being refined.
Descendants of freshwater green algae spread onto bare ground, becoming the first true land plants.
See it on the Life map →What happened
Land plants descend from freshwater green algae. Their earliest traces are tough-walled spores about 470 million years old, from Argentina and elsewhere; molecular clocks suggest an origin perhaps 500 million years ago or earlier. The pioneers were small, moss-like mats without roots or internal plumbing. They coped with dry air and ultraviolet light using waxy coatings, spores wrapped in a resistant polymer, and fungal partners. Before them, land held only microbial crusts.
Why it matters
Plants built soil, added oxygen, changed rock weathering and climate, and supplied the food and shelter that let animals follow onto land.
Think of it like
Like the first homesteaders on raw land: rough, small settlements that made the ground livable for everyone after.
The evidence (fossils, genes, rocks)
Fossil spores and plant fragments from Ordovician rocks, the anatomy of living mosses and liverworts, and DNA showing land plants nest within green algae.
Still debated
When plants first reached land (Cambrian or Ordovician), and which living group of land plants branched off first, are still debated.
Inside this (6)
Connections (6)
▸Plants colonize land may have helped trigger Late Ordovician mass extinctionDebated
The connection
One hypothesis: early moss-like plants sped up the breakdown of rock, releasing phosphorus and locking away carbon dioxide. Less carbon dioxide meant a cooler planet, helping ice sheets grow over Gondwana, which in turn drove the extinction. Lab experiments showed living mosses can substantially speed rock weathering.
When and how
Proposed by Timothy Lenton and colleagues in 2012; the cooling would have run from about 470 to 445 million years ago.
How sure are we?
Uncertain: the timing fits and experiments support the mechanism, but how much land early plants covered is unknown and other cooling causes exist.
Debates and open questions
Weathering of fresh volcanic rock, lower volcanic carbon dioxide or changes in ocean circulation might explain the cooling without plants.
▸Plants colonize land relied on Plant–fungus partnerships (mycorrhizae)Strong evidence
The connection
The first land plants had no roots. Fungal partners threaded through bare grit, extracting phosphorus and water and passing them to the plants in exchange for sugars. Many scientists think this partnership is what made life on rocky, soil-less ground possible for early plants.
When and how
From the earliest land plants, perhaps 470 million years ago or before; seen clearly in Scotland's Rhynie chert, about 407 million years ago.
How sure are we?
Fungi inside cells of Rhynie plants, fossil fungal spores about 460 million years old, and symbiosis genes shared by liverworts and other land plants.
Debates and open questions
Whether fungi were needed for the first step onto land or joined soon after, and which fungal groups were involved first.
▸Plants colonize land led to Vascular plants (Cooksonia)Well established
The connection
The first land plants were short because they had no plumbing to move water. Some evolved xylem, tubes of reinforced cells that carry water up from the ground and stiffen the stem. That let plants such as Cooksonia stand taller, a few centimeters at first, and branch, setting up later trees.
When and how
Silurian period, about 430 million years ago; Cooksonia fossils come from Ireland, Wales, the Czech Republic and elsewhere.
The evidence
Fossil stems with preserved water-conducting cells, and the shared anatomy and DNA of living vascular plants.
Debates and open questions
Whether all Cooksonia had true xylem is uncertain, and how mosses and liverworts relate to vascular plants is still debated.
▸Plants colonize land provided food and shelter for Arthropods walk onto landStrong evidence
The connection
Plants turned bare ground into habitat. Their living and dead tissue fed early millipedes and mites, many of which ate decaying plant matter, while low plant mats kept the ground moist and shaded. Predators such as early arachnids followed the plant-eaters.
When and how
Silurian and early Devonian, about 430–400 million years ago; best seen in the Rhynie chert, Scotland, about 407 million years ago.
How sure are we?
The Rhynie chert preserves arthropods among plant stems, plant tissue damaged by feeding, and fossil droppings full of plant material.
Debates and open questions
Whether some arthropods reached land before plants, feeding on microbial crusts, as Cambrian trackways may hint.
▸The ozone layer made land safer for Plants colonize landStrong evidence
The connection
Life on bare ground faces full sunlight, including ultraviolet rays that damage DNA. The ozone layer, which built up after oxygen rose about 2.4 billion years ago, filtered most of that UV. Together with protective pigments and tough spore walls, it let plants survive in the open. It was a precondition, not a trigger.
When and how
The shield formed after about 2.4 billion years ago; plants reached land about 470 million years ago, so it was in place long before.
How sure are we?
The physics of UV absorption and models of the oxygen–ozone link; the role is accepted in principle but hard to measure for the Ordovician.
Debates and open questions
How strong the shield was before oxygen neared modern levels, and whether a later oxygen rise thickened it just before plants moved onto land.
▸Chloroplasts: algae capture cyanobacteria later powered Plants colonize landWell established
The connection
Every land plant inherited chloroplasts, the light-harvesting compartments that began as cyanobacteria captured by an algal cell roughly a billion years earlier. Land plants descend from green algae carrying these chloroplasts, so the same photosynthesis machinery that evolved in water ran the first plants on land.
When and how
Chloroplasts arose roughly 1.9–1.2 billion years ago in early algae; their green-algal descendants moved onto land about 470 million years ago.
The evidence
Chloroplasts have their own DNA, closely related to that of cyanobacteria, and land-plant chloroplasts closely match those of green algae.
Debates and open questions
When the original capture happened is debated, and how land-plant chloroplasts adapted to stronger, drier sunlight is still studied.