According to Earth System Science Education, the first land animals appeared toward the middle of the Paleozoic Era, in the late Silurian period. The earliest animals to adapt to the land were small arthropods similar to mites, spiders and scorpions.
The challenge of adapting from life in the sea to life on land was accomplished due to the jointed exoskeletons of arthropods. This prevented them from drying out and also provided support against the stronger effect of gravity. Additionally, their limbs were not dependent on water for locomotion. The earliest land plants were also introduced in the late Silurian period, and Europe's mountains were shaped during this time.