They were similar to modern tree ferns and cycads, although none of the original species survive today. Most trees long outlive people, 100-200 years being a typical lifespan. During the process of photosynthesis all green plants take in carbon dioxide and give off oxygen. Primitive plants were responsible for converting the poisonous atmosphere of early Earth into an oxygen-rich atmosphere that supports animal life. Soil benefits from trees, as their far-reaching roots hold the soil in place, preventing erosion.
Trees improve soil quality as their leaf litter makes perfect compost.
Some trees, for example acacias, have bacteria living in their roots. The bacteria convert nitrogen from the air into nitrates which the tree can use to grow and reproduce, whilst the soil is also enriched. The leaves of trees are eaten by many insects as well as monkeys, elephants, giraffes, kudus and bushbucks. Even fallen dead leaves are eaten - they are a favourite food of the blue duiker. Flowers are eaten by monkeys, and nectar by birds, insects and bats.