Life on the planet started astonishingly early. The first living organisms, in the current model of evolution, are thought to be Prokaryotes1. The oldest known fossilised prokaryotes have been dated to approximately 3.5 billion years ago, only 1 billion years after the formation of the Earth's crust.

Eukaryotes2 are more advanced organisms with complex cell structures, each of which contains a nucleus. Although incredibly hard to determine their origin, they are thought to have developed 1.6–2.1 billion years ago, although some research2 suggests eukaryotes being present even earlier than this.

Around 1.1 billion years ago multicellular3 organisms are thought to have started to develop, most likely similar in form to plants such as green algae. 200 million years later true multicellularity had also evolved in animals similar in nature to today's sponges, which are organisms which can reassemble themselves.

Animals4, in the most basic sense of the word, are considered to have evolved from Eukaryotes. Fossils of early sponges have been discovered in 665 million year old rock. Later on, around 560 million years ago, some highly significant fossils of an organism which was named Charnia4.1 were discovered. These enigmatic early animals were anchored to the sea floor where they are thought to have absorbed nutrients.

Around 450 million years ago, during the Ordovician Period, land plants appeared, although new evidence may suggest that complex photosynthetic plants developed over 1000 million years ago. Studies of fossils from the Devonian Period 416–359 Ma5.1 indicate that land plants had evolved features we recognise today, such as leaves, roots, and secondary wood. Towards the end of this time seeds had evolved.