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Jan 1, 1000
Mini-threshold 1: Simple bacteria - prokaryotes
The first living organisms consisted of single cells and were so small they would be invisible to the naked eye. They are called prokaryotes and huge numbers of them still exist today. There are microscopic fossils of what seem to be prokaryotes dating from about 3.5 billion years ago. -
Period: Jan 1, 1000 to Mar 13, 1400
Thresholds of Life
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Feb 4, 1020
Mini-threshold 2: Photosynthesis
About 3.5 billion years ago, some prokaryotes gained the ability to use energy from sunlight, in combination with water and carbon dioxide, to form molecules such as sugars which could store energy. As a result, living organisms learned to use and store sunlight, an entirely new source of energy. -
Apr 8, 1130
Mini-threshold 3: Eukaryotes
About 2 billion years ago, eukaryotes began to appear (like the prokaryotes, they were single-celled, but many of which were thousands of times larger and more complex). Biologists believed they formed through a merger of prokaryotes because they contained interal structures. Eukaryotes were capable of sexual reproduction, which meant that they combined their DNA with others and therefore sped up the process of evolutionary change. -
May 12, 1270
Mini-threshold 4: Multi-celled organisms
Roughly 600 million years ago, multi-celled organisms formed from eukaryotes combining All the cells in the organisms had the same DNA, but different cells used parts of the DNA code to form specialized cells such as red blood cells, neurons, bone cells and muscle cells. It is theorised that an increase in atmospheric oxygen allowed for multi-celled organisms to form and later move onto dry land. -
Jul 16, 1330
Mini-threshold 5: Brains
Some species evolved with spinal cords and nerve cells which formed the first brains. Neuron networks were able to receive infromation from the outside world and form maps of the environment, allowing organisms to respond to their surroundings in a variety of ways. Neuron networks would later meet specific conditions to form conciousness. -
Aug 20, 1360
Mini-threshold 6: To land
Roughly 475 million years ago, some organisms, such as plants and fungi left the oceans and moved to land. Although there were plentiful potential resources on land, moving from one environment to another was difficult for living organisms. For example, they needed to develop a spacesuit-like skin to avoid drying out and had to find ways to reproduce out of water. -
Oct 24, 1380
Mini-threshold 7: Mammals
The first mammals appeared approximately 250 million years ago, but were overshadowed by reptile species such as dinosaurs. The extinction of dinosaurs 65 million years ago allowed mammals to perform a process named evolutionary radiaton, which meant different species could adapt to different environments to survive. Mammals also are warm-bloooded, have large brains and their young pass their embryonic stage inside their mothers' bodies.
