Solar system was a swirling mass of gas and debris, which was pulled together by gravity and eventually formed the Sun. The Sun became the center of the solar system, as the other debris formed smaller planets around it.
(4.6 BYA)Creation of the Earth
Left over debris and gas from the creation of the Sun continued to collide. These collisions were at such high speeds that they generated enough thermal energy to fuse the debris together. As more debris continued to collide and fuse, the earth was eventually formed. The earth was a perfect size and in a perfect position to allow for the formation of life, Scientists know the age of the Earth as a result of radiometric dating.
(4 BYA) First Rocks, Crystals, and Organisms
At this time the bombardment of the Earth by debris stopped, thus allowing the Earth's surface to cool and form rocks and crystals. The cooler surface of the earth allowed organic molecules to accumulate on the surface of the earth. Some scientists believe that these organic molecules may have accumulated and created self-replicating RNA, which would later become the first heterotrophs, and later chemosynthetic autotrophs, similar to archaea bacteria.
(3.5 BYA) Possible Photosynthetic Organisms.
Cells in the form of stromatolite structures are found. Today, stromatolite structures are often indicative of cyanobacteria which is photosynthetic. The similarities in structure suggest the prehistoric cells that were found were photosynthetic as well, and possible ancestor of cyanobacteria.
(3 BYA) Photosynthetic Organisms are known to exist
Photosynthetic life forms are known to have existed during this period due to chemical traces as a result of photosynthesis and also the stromatolite fossils which date to 3.5 BYA. The atmosphere also began to have more oxygen, which was often fatal to these organisms because they destroyed coenzymes vital to life. Photosynthetic organisms had to adapt to the increasingly oxygen rich environment, which resulted in the precursor of aerobic respiration.
(2.2 BYA) Earth Develops into current form
Earth develops into what it looks like today. Atmospheric conditions began to look the same as today with more oxygen being present in the air, which sustained photosynthetic life forms.
(2 BYA) Oxygen Levels
Oxygen levels in the atmosphere reach current levels, which helps to sustain photosynthetic life.
(1.5 BYA) Eukaryotic Organisms were created by Endosymbiosis
According to the endosymbiotic theory, certain organelles contained inside eukaryotic organisms came from free-living aerobic bacteria that were taken into an anaerobic bacteria. These aerobic bacteria provided energy for the anaerobic bacteria in return for protection. Eventually the aerobic bacteria would become mitochondria, or chloroplasts if they were photosynthetic.
(1 BYA) Ozone Layer is Formed
UV radiation from the sun reacts with the Oxygen in the atmosphere to create ozone. Ozone formed a layer around the Earth which helped to absorb UV rays, which are harmful to organisms. This allowed life to begin to develop on land.
(1590) First Microscopes
First Microscopes developed in 1590, but the makers are hard to identify. Galileo made the first compound microscope, which is when it was give that name. Microscopes began to be commonly used in science in the 1660s and 1670s.
(1668) Redi's Experiment
Francesco Redi, is best known for his experiment that denied spontaneous generation. In the experiment, one sample of meat was covered and another was left untended. They where then left out to see if spntaneous generation occured. The results of the experiment where that the covered meat had not maggots while the uncovered meat had sprouted maggots.
Spallanzani's experiment (1700s
Spallanzani's experiment attempted to disprove the theory of spontaneous generation. He theorized that life could only come from other life. He thought that if he boiled a flask to kill all the organisms in it and then sealed it, it would remain clear because no life forms could reproduce in it, thus disproving spontaneous generation. The scientific community did not accept his theory because they believed the boiling process destroyed the vital force which causes spontaneous generation
(mid- 1800s)Pasteur's Experiment
A variation of Spallanzani's experiment, Pasteur's experiment disproved vital force once and for all by exposing the broth to the air, and the "vital force", but designing the flask in such a way that bacteria could not get in due to gravity.After a year the flask remained clear, so Pasteur then broke off the altered part of the flask, and within a day the flask grew brown with the addition of microorganisms. This proved that microorganisms came from the air and didn't spontaneously generate.
(1905) Radiometric Dating is invented
Radiometric dating was figured out by the famed physicist Ernest Rutherford. It uses the half-life of a radioactive isotope and the quantity of it in the sample which needs to be dated. That sample is then compared to a sample that maintains the same amount of the radioactive isotope over time. From there, simple logarithmic equations can determine the age of the sample.
(1920s) Oparin's Hypothesis
Soviet scientist Alexander Oparin hypothesized that organic compounds were creating when reactions occurred between various gasses, such as ammonia, hydrogen gas, water vapor, and methane, that were present at the time. These gasses formed simple organic compounds which collected in Earth's lakes and seas, and when they were exposed to UV radiation or lightning, they acquired the energy necessary to start a complex chemical reaction, thus forming macromolecules
(Mid 1900s) Fox Studies Cell-Like Structures
In the mid 1900s scientist Sydney Fox and others did extensive research into inorganic sructures which could have become the first cells. The two that were studied were microspheres and coacervates. Microspheres have a protein membrane and have the ability to grow, while coacervates have the ability to "reproduce" by forming smaller coacervates. Both these structures showed how cellular processes can occur in inorganic structures, but both structures still lacked RNA and DNA.
(1953) Urey And Miller's Experiment
In 1953 Stanley Miller and his professor Harold Urey developed an experiment to test Oparin's hypothesis. They simulated the atmosphere of the Earth at the time and then exposed the gasses to electricity generated by two electrodes. The electricity stimulated chemical reactions which yielded organic compounds such as amino acids and nucleotides. The importance of this experiment is being called into question due to new information on the composition of the atmosphere at the time.
(1966) Lynn Margulis Publishes Endosymbiosis theory
The endosymbiosis theory proposes that eukaryotic organisms were first formed when anaerobic bacteria absorbed aerobic bacteria, forming a symbiotic relationship. In this relationship the aerobic bacteria provided energy in return for protection. Eventually the bacteria became the organelles known as mitochondria, or chloroplasts if the bacteria were photosynthetic.
(1980s) Cech Discovers and Coins Rybozymes
Thomas Cech discovered a single celled eukaryotic organism that used RNA to catalyze chemical reactions. He called these RNA ribozymes. It was discovered that these ribozymes could catalyze their own replication, thus making it possible that these RNA were the first self replicating organic molecules. It is hypothesized that the RNA molecules evolved to became better suited to gather nucleotides for replication and eventually merged with a microsphere or coacervate to form early cells.