425 mya: Vascular land plants
Early vascular land plants -- so named for internal veinlike tubes
that circulate water and nutrients -- send shoots skyward to capture sunlight and
release reproductive spores to the winds. Most grow only a few centimeters tall. With
deeper root systems than earlier plants and a rigid stem to support upright posture,
they are now equipped to colonize more of Earth's surface.
425 mya: Great mountain ranges form
Extensive mountain ranges form when two of Rodinia's former land
blocks, Laurentia and Baltica, collide. The crust in the collision zones buckles,
and the rocky formations that result comprise the earliest parts of the Appalachian
mountain range, as well as corresponding mountain belts in present-day Greenland,
Scotland, Ireland, and Norway.
420 mya: Arthropods on land
Arthropods are the first animals to adapt to land. In most ways,
they were pre-adapted to life on land. By the time they move ashore, they have
already evolved an ultralight body and spindly but strong legs to counteract the
force of gravity. Their hard outer shells, called cuticles, provide protection and
retain moisture. Spiders, centipedes, and mites are among the earliest land variants.