Plant life first appeared on land during the Ordovician period, between 495 and 443 million years BCE. One 2001 study from Penn State University claims that plants and fungi first appeared on land 700 million years BCE, but this has not yet become accepted by the larger scientific community.
Though plants first moved onto the land during the Ordovician period, plant life had already appeared in the oceans some time earlier than this. Single-celled plant organisms appeared over 2 billion years BCE, and multicellular algae, the ancestors of modern plants, appeared as early as 1 billion years BCE. It was not until the Carboniferous period that plant life expanded from the coastlines and edges of lakes and began to more fully resemble modern plants.