Timeline Of The Evolution Of Life On Earth

Matt McVicar (mm4819) and Stephen Reid (sr8243)

Timeline of the evolution of life on Earth Biological events

Between 4500 and 2500 Mya

RNA, which can both store information and act as an enzyme, may have supported the first pre-cellular life. Eventually DNA takes over the data storage role due to its greater chemical stability, whilst proteins take over catalytic function due to the variety of amino acids providing greater flexibility in catalysis. DNA soon develops inside enclosing protective membranes, which provide a stable environment for their

3900 - 2500 Mya Prokaryotic life Prokaryotes (single-cellular organisms with no nucleus) first appear. They can obtain energy from inorganic substances (promoting survival in harsh environments) and later use glycolysis to generate ATP, which is still used in almost all organisms to this day.

(not to scale)

Physical events ~4500 Mya Formation of the Earth Earth forms by accretion disc revolving around the sun. Moon stabilises the Earth’s gravitational axis The moon is formed. One possible explanation is that Earth and the planet Theia collide, blasting a large amount of debris into the earth's orbit.

4100 Mya Crust solidification The surface of the earth cools sufficiently for the crust to form.

3900 Mya Late heavy bombardment The Earth is heavily bombarded by meteors. It is unlikely that any life present on the Earth survived this turbulent period, as the oceans boiled away completely. It is also possible that new life was brought to Earth during this period.

3500 Mya Last common ancestor The last common ancestor of all life currently on the planet. The earliest bacterial, anoxygenic photosynthetic systems appear, using hydrogen and sulphur as electron donors.

3000 Mya Oxygen from photosynthesis Photosynthesizing cyanobacteria use water as a reducing agent, producing oxygen as a waste product. The oxygen subsequently poisons many existing lifeforms.

2100 Mya Eukaryotic life Eukaryotic cells appear featuring a nucleus, membrane and membrane-bound organelles such as mitochondria. They may have developed from the phagocytosis of prokaryotes.

1200 Mya Sexual reproduction Some unicellular life starts practicing sexual reproduction, allowing populations to respond more rapidly to a changing environment. Multicellular life First evidence of multicellular life. For the moment, these remain complex bundles of single cell colonies.

850 - 630 Mya Snowball Earth The most severe ice age of the last billion years sees ice cover the entire planet, possibly reducing the diversity of life. The period is ended by the accumulation of greenhouse gases produced by volcanoes.

580 Mya First lifeforms to possess nerves, muscles and a body 580 - 542 Mya Ediacara biota The first complex multicellular life evolves soon after the thawing of the glaciers in the form of the Ediacara biota. Their strange form and apparent disconnectedness from later organisms suggests a 'failed experiment' in multicellular life, with later multicellular life independently re-evolving from unrelated single-celled organisms.

550 Mya Flatworms are the earliest animals to possess a brain

580 - 500 Mya Cambrian Explosion Evolution accelerates by an order of magnitude (as measured in terms of the extinction and origination rate of species) with the appearance of diverse life, including modern land animals. Possible explanations include an increase in oxygen concentration or an arms race between predator and prey.

540 Mya Acorn worms have a circulatory system with a heart that also functions as a kidney Oxygen accumulates in the atmosphere leading to the formation of the ozone layer. This acts as a shield from the sun's damaging ultraviolet radiation and allows complex life

505 Mya The first vertebrates appear in the form of jawless fish

475 Mya Primitive plants are move onto land, having evolved from green algae living on the edge of lakes

450 Mya Ordovician–Silurian extinction

364 Mya Late Devonian extinction 363 Mya Carboniferous period Insects and arachnids roam the land, including Basal Dictyoptera relative of cockroaches. The dominant fish present were Elasmobranchs (sharks and their relatives). The most common plant life at this time were ferns, vines, and scale trees. Earth is now recognisable to a human.

315 Mya Some freshwater fish develop rudimentary limbs and lungs marking the start of amphibians. At this stage, the limbs were probably only used for crawling through mud. 300 Mya From amphibians come the first reptiles, with the ability to reproduce and lay eggs on dry land. Compared to amphibians reptiles have an advanced nervous system featuring 12 pairs of cranial nerves.

230 Mya Dinosaurs Gymnosperm forests dominate the land; herbivores develop huge digestive organs necessary for processing the nutrient-poor plants. These were the first examples of dinosaurs.

251 Mya Permian–Triassic extinction The Earth's most severe extinction wipes out up to 96% of marine life and 70% of terrestrial vertebrates. Suggested causes range from impact events to increased volcanism to a shift in ocean currents driven by climate change. Those species which survive tend to have control over circulation and advanced gas exchange mechanisms.

220 Mya The first mammals evolve from reptiles, with a constant body temperature, milk glands for their young and a neocortex region of the brain. 200 Mya Triassic–Jurassic extinction 200 Mya First evidence of viruses

130 Mya First examples of flowering plants Angiosperms produce pollen which attract insects and other animals, driving a period of co-evolution through symbiosis. 65 Mya Cretaceous-Tertiary extinction The extinction of approximately 50% of all life, including all dinosaurs except modern birds. 35 Mya Evolution of grasses Grasses evolve from the angiosperms and proceed to dominates much of the landscape.

Modern era Modern man Humans make a significant effect on the planet's ecoystems and climate. In the 1980's, man’s ecological footprint outstrips the Earth's biocapacity.

Modern era Holocene extinction Megafaunal extinction in the Americas results in fierce debate regarding the influence of man on these habitats.