Timeline for Life on Earth
Rough Timeline for Life on Earth:
This is a rough timeline for life on Earth. It is difficult to determine dates for specific events and the furthur back in time you go, the more uncertain the dates are. The fossil record is very incomplete so it can be difficult to establish when particular evolutionary changes happened. It's like a movie with most of the frames cut out.
- 4.5 billion years ago earth formed
- 4 billion years ago the oceans started forming
- 3.8 billion years ago the first life on earth formed
- 3.5 billion years ago we have the earliest known fossils of life on earth
- 2.4 billion years ago, oxygen starts to build up in the atmosphere. There are a few different theories on why oxygen starts building up at this time.
- 2.3 billion years ago, earth almost completely freezes over into a snowball earth. When the ice melts it adds more oxygen into the atmosphere.
- 2.15 billion years ago the first mainly undisputed fossil evidence of cyanobacteria and photosynthesis. This is cells taking in sunlight and carbon dioxide to produce energy and giving off oxygen. Some scientists think photosynthesis had been going on for a while by this point and is one of the reasons for oxygen starting to build up 2.4 billion years ago.
- 2 billion years ago the first eukaryotic cells (complex cells) formed
- 1.5 billion years ago the eukaryotes split into three groups. These make up the ancestors of modern plants, fungi and animals. At this time it’s believed all three are still single celled organisms. Also scientists are unsure in what order they formed first.
- 900 million years ago the first multicellular life forms. Scientists are not sure how or why this happens but there are a few theories.
- 770 million years ago, earth freezes over again into a snowball earth
- 630 million years ago, some animals formed a bilateral system. This means they have a defined top and bottom as well as front and back.
- 565 million years ago, animal fossil trails indicate some animals are moving under their own power.
- 540 million years ago, the first animals that have a primitive backbone emerge
- 535 million years ago, the Cambrian explosion began. This is when many new body layouts appear in a relatively short time.
- 530 million years ago, the animal with the first true backbone appears
- 500 million years ago, fossil evidence shows that animals were exploring land
- 489 million years ago, the Great Ordovician Biodiversification event began. This leads to a great increase in the diversity of animals and plants.
- 465 million years ago plants began colonizing the land
- 425 million years ago, the coelacanth splits from the rest of the lobbed finned fish. This fish is still alive today.
- 400 million years ago, the oldest known insects were alive
- 397 million years ago, the first 4 legged animals evolve
- 385 million years ago, the oldest known fossilized tree dates from around this time
- 375 million years ago, Tiktaalik, an intermediate between fish and four-legged land animals, lives around this time. Many scientists point to this as an example of evolutionary changes that led to fish leaving the water and walking on land.
- 250 million years ago, the Permian period ends with the greatest mass extinction in earth’s history. This mass extinction paves the way for the dinosaurs.
- 200 million years ago, the Triassic period comes to an end with another mass extinction. Also mammals evolve warm-bloodedness.
- 150 million years ago, Archaeopteryx, the famous “first bird”, lives in Europe
- 130 million years ago, the first flowering plants evolve
- 93 million years ago, The oceans become starved of oxygen and twenty-seven per cent of marine invertebrates are wiped out.
- 75 million years ago, The ancestors of modern primates split from the ancestors of modern rodents and lagomorphs (rabbits, hares and pikas).
- 65 million years ago, The Cretaceous-Tertiary (K/T) extinction wipes out a swathe of species, including the dinosaurs. The extinction clears the way for the mammals, which go on to dominate the planet.
- 55 million years ago, The Palaeocene Eocene extinction, a sudden rise in greenhouse gases, sends temperatures soaring and transforms the planet, wiping out many species in the depths of the sea – though sparing species in shallow seas and on land.
- 47 million years ago, The famous fossilised primate known as”Ida” lives in northern Europe
- 6 million years ago, "humans" diverge from their closest relatives; the chimpanzees and bonobos. Shortly afterwards, hominins begin walking on two legs.