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(5 BYA) Early Solar System
The solar system was made up of only gas and dust. -
(4.6 BYA) Formation of Earth
Earth grew when gravity caused debris to collide together and stick to form planets. For millions of years, Earth was constantly being hit by space debris. The impact melted the rock and caused its surface to be molten. -
(4 BYA) Atmosphere
Volcanoes formed Earth's atmosphere by emmiting gases. The early atmosphere was very toxic and did not contain oxygen gases. -
(4 BYA) First Life Forms
The first forms of life began to populate the Earth. They were cell-like organisms called Methanosarcina barkeri. They produce methane during metabolism abnd resembled archea, and they were able to survive in the extreme environment. -
(3.5 BYA) Stromatolites
Stromatolites were layers of rock made up of Lynbgya cells. They contain cyanobacteria. Stromatolites also have different fossils, which can help scientists study the kinds of organisms that lived when the rocks were forming. -
(3 BYA) New Plants
Life forms on earth became photosynthetic; they started using organic molecules to create more organic molecules. Life forms used to undergo chemosynthesis, which used inorganic molecules to create organic ones. After cells started using photosynthesis, oxygen was released into the atmosphere as a byproduct. Since there was oxygen, aerobic cells, which needed it to survive, could start to form. -
(2.2 BYA) Earth
Earth is very similar to what it is today. -
(2 BYA) Oxygen Levels
Oxygen levels reach today's levels in the atmosphere. -
(1.5 BYA) First Cells
A type of small aerobic prokaryote was contained in a larger anaerobic prokaryote, where it lived and reproduced itself. This is called endosymbiosis. -
(1 BYA) Ozone
Ozone was formed. It was created when oxygen gases reached the upper part of the atmosphere. The ultraviolet rays from the sun split some of the compounds, which reacted with the gas to create O3, or the ozone. It helped early life forms thrive by absorbing the sun's rays, so they were not so dangerous once they reached Earth. -
(1665) Light Microscope
Robert Hooke copied Leeuwenhoek's light microscope and improved it. He also used it to discover microorganisms living in water droplets, which did not support the theory of the origin of life, spontaneous generation. -
(1668) Redi's Experiment
Redi wanted to disprove spontaneous generation. He had an open flask and a sealed flask, both with rotten meat inside. When the flies had access to the meat maggots appeared, but with no access tot he meat, njo maggots appeared. This shows that in order for maggots to appear adult flies need to be there as well. -
(1768's) Spallanzani's Experiment
Spallazani worked to further prove Redi's experiment on spontaneous generation. He took two flasks that contained chicken broth and boiled them to kill existing microorganisms. He covered one, but left the other open. After a few days, the uncovered one was cloudy, showing the existance of microorganisms in the air. -
(mid-1800's) Pasteur's Experiment
Louis Pasteur performed an experiment similar to Spallanzani's, but instead of using a flask with a short, straight neck, he boiled the chicken broth in a flask with a long, curved neck. After a year, the uncovered broth was still clear. When he cut off the neck, the chicken broth grew cloudy after a day. This proved that microorganisms exist in the air because they were trapped in the first curve of the neck. -
(1900's) Radiometric Dating
Radiometric dating can be used to figure out the age of a material. It compares the percentage of radioactive isotopes to stable isotopes. The time it takes for half of the sample to decay is its half life. By using radiometric dating, scientists have been able to figure out the age of the Earth, among other ancient things, -
(1922) Oparin's Hypothesis
Oparin thought that early atmosphere contained annonia, hydrogen, water vapor, and compounds made of hydrogen and carbon. He also thought that at high temperatures, these gases could have formed organic compounds like amino acids, which could have led to life. -
(1953) Urey and Miller
Urey and Miller tested Oparian's atmosphere hypothesis by putting all the predicted molecules in a chamber. They sent lighting through the chamber to make the molecules react, and they formed amino acids, supporting Oparian's hypothesis. -
(1957) Microspheres and Coacervates
Sidney Fox studied the structures that may have led to the first cells. The structures were microspheres, which were spherical and made up of proteins, and coacervates, which were collections of droplets made up of molecules of different lipids. -
(1982) Thomas Cech
Thomas Cech found that certain kinds of RNA found in eukaryotic cells are able to act as a catalyst for chemical reactions, like enzymes. He called this kind of RNA "ribozymes." -
(mid-1960's) Endosymbiosis
Lynn Margulis theorized that the origin of eukaryotic cells happened through endosymbiosis. Endosymbiosis is when a smaller prokaryotic cell is engulfed in a larger prokaryotic cell, and they continue to thrive. They also replicate, making more copies of the cell. Over time, they evolved organelles. With the creation of eukaryotic cells, more complex organisms began to form.
