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 o