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Threshold 1: Simple bacteria - prokaryotes
Prokaryotes were the first living organisms, single celled, and so small you would need a microscope to see them. They first formed near cracks in the ocean floor, and all have a vell wall through which food can enter and wastes can exit, as well as the DNA needed for them to reproduce.There are microscopic fossils of prokaryotes dating back 3.5 billion years. -
Threshold 2: Photosynthesis
Some of the prokaryotes obtained the ability to use energy they retrieved from sunlight (and an almalgamation of water and carbon dioxide) to for molecules which could store energy - this is an ability that due to this evolution, all plants nowadays can utlilise (most living organisms use sunlight as their primary source of energy as well). A side effect of photosynthesis was the increased production of oxygen. -
Threshold 3: More complex cells - eukaryotes
About 2 billion years ago, eukaryotes began to appear (which were larger and far more complex than prokartyotes, though still single-celled organisms). They probably formed as a merger of prokaryotes, and contain internal structures like mitochondria. They were also capable of sexual reproduction, which meant they combined their DNA with others before reproducing which sped up the process of evolutionary change. -
Threshold 4: Multi-celled organisms
600 - 540 million years ago, multi-celled organisms started to be formed from the combining and specialising of eukaryotic cells. All the cells in the organisms had the same DNA, but they all used different parts of the DNA's code to form cells such as neurons, bone cells and muscle cells (this evolution may have been made possible by an increase in atmospheric oxygen). They eventually evolved to survive on dry land. -
Period: to
Threshold 4: Multi-celled organisms
600 - 540 million years ago, multi-celled organisms started to be formed from the combining and specialising of eukaryotic cells. All the cells in the organisms had the same DNA, but they all used different parts of the DNA's code to form cells such as neurons, bone cells and muscle cells (this evolution may have been made possible by an increase in atmospheric oxygen). They eventually evolved to survive on dry land. -
Threshold 5: Brains
Some species began to evolve spinal cords and large bunches of nerves, which formed the first primitive brains. However, for a while these were largely unconscious until the evolution of large networks of nerce cells (which form the conditions we define now as consciousness). -
Threshold 6: To land
About 470 million years ago certain organisms left the oceans and lived on land. This was extraordinarily difficult because they needed to develop skins like spacesuits to avoid drying out (as well as ways of reproducing out of water). -
Turning point 7.1: Mammals
The first mammal-like creatures (possibly) appeared 250 million years ago, but for the next 200 million years were obscured by existing reptile species (such as dinosaurs and crocodiles). -
Turning point 7.2: Extinction of Dinosaurs
About 65 million years ago, dinosaurs became extinct, which lead mammals to adapt to fill the gaps left by them (which biologists call evolutionary radiation). This is when mammals began to diversify.
