The Bug-Filled Swamps of Deep Time

By 320 million years ago, the planet was warm at the equator and cold at the poles. As ice sheets spread out from the South Pole, humid swamps expanded along equatorial coasts, occupied by soaring lycopsid trees, giant tree ferns, and horsetails. Some of the first seed plants (the most common kind of plant today) inhabited drier environments. In this mural, the denser forest at left holds the kind of peaty swamp that formed coal deposits, which humans have mined for fuel. Insects first appeared and took flight in the preceding Devonian Period, but in the Carboniferous, boosted by higher oxygen levels, they developed new forms—and huge sizes. Though smaller now, insects and other arthropods still dominate land ecosystems, composing nine-tenths of all living animals.

Lepidodendron and other polelike lycopsid trees covered vast tropical tracts. They could grow for a century without branching, then sprout a crown with spore-filled cones, reproducing just once before dying.

Tree-sized ferns that resemble this Pecopteris arborescens still exist today.

A less common resident of Carboniferous swamps, tree-sized horsetails like Annularia spinulosa grew up to 50 feet tall. Horsetails still grow in wet habitats today but are much shorter.