Final answer:
Life transitioned onto land during the Phanerozoic Eon, specifically in the Devonian period of the Paleozoic Era, which occurred about 400 million years ago. Early tetrapods were among the first vertebrates to make this move, leading to the 'age of the amphibians.'
Step-by-step explanation:
Life made a significant transition from water to land in the Paleozoic Era, which is part of the Phanerozoic Eon. During the earlier periods of the Paleozoic, such as the Ordovician, land was first colonized by primitive plants. However, it wasn't until the Devonian period, 400 million years ago, that the first animals ventured onto land. These early animals, which included vertebrates, had to develop adaptations such as a resistant outer skin and limbs for locomotion. This period of history is notable for the diversification of vertebrates and the establishment of ecosystems that supported terrestrial life.
The first vertebrates to move onto land were early tetrapods, who had access to new nutrient sources and fewer predators, leading to the 'age of the amphibians' during the early Carboniferous period. Meanwhile, plants continued to evolve, create microclimates, and support the burgeoning complexity of life on land. The evolution of plants and animals on land paved the way for the great diversity of life we find on Earth today.