Algae have a long fossil record on Earth, dating to the Precambrian (more than 550 million years ago). Fossil cells from an 850-million-year-old Australian site may even be from algae. Being soft and fragile, algae do not preserve well. Also, the biochemical characteristics used to identify algae are usually absent in fossils. Many algae fossils are just shape outlines left on rocks. Some algae leave a record of their activities, such as those which precipitate calcium carbonate, leaving deposits behind. When algae came onto land, they started all terrestrial life. Paleobotanists point to a group of simple green algae called Charophyceae as the likely ancestors to all green plants. Sheets of plant cells have been found at Ordovican sites (about 450 million years old). Once plants became terrestrial, the way was paved for animals to live on land as well.