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(5 BYA) Solar System
The solar system was a swirling mass of gas and dust. These particles were what would eventually form planets in the solar system. -
(4.6 BYA) Formation of Earth
Gravitational forces begin to pull debris together to form the earth. It begins to grow from colliding with other debris in the solar system. -
(4 BYA) Formation of Earth Complete
At this point in time, the earth was essentially finished forming, and had reached about the size it is today. -
(3.5 BYA) Stromatolites Appear
Stromatolites began appearing on the Earth. These were colonies/structures for Lynbgya, which is a type of cyanobacteria. -
(3 BYA) Photosynthetic Life Develops
Some life started to become photosynthetic. Oxygen at this time, which was harmful to the life on this planet, was now harmless due to the use of aerobic respiration. -
(2.2 BYA) Earth Looks Like it Does Today
At this point in time, the earth, fully formed, had developed into an earth that looked similar to the earth that we know today. -
(2 BYA) Oxygen Reaches Today's Levels
At this point, the amount of oxygen in the atmosphere had reached the same amount that is in our atmosphere today. -
(1.5 BYA) Prokaryotes Engulfed by Larger Prokaryotes
Smaller prokaryotes were engulfed by larger ones, and began to reproduce. Scientists believe that this action, endosymbiosis, created the first mitochondria and choloroplast. -
(1 BYA) Ozone Forms
An ozone layer formed, protecting organisms from ultraviolet radiation, which can be harmful to DNA. This allowed organisms to exist on land. -
(1665) First Microscopes
In 1665, one of the first microscopes (an early light microscope) was used by Robert Hooke to observe cork. He became the first man to see individual cells, using a microscope. -
(1668) Redi's Experiment
Redi discovered that flies come from other flies by his experiment involving the meat in the jars. The flies could only reach the meat in the uncovered jar, which is where they laid their eggs. This disproved the theory that flies came from rotting meat. -
(1700s) Spallanzani's Experiment
Spallanzani’s Experiment tested the hypothesis of spontaneous generation of microorganisms. He heated broth until all microorganisms would have died, then noticed that no more microorganisms appeared, disproving the hypothesis that spontaneous generation existed. However, his experiment was actually thought to have caused the air to lose its “vital force” by heating it, and that this was what caused the lack of spontaneous generation. -
(Mid-1800s) Pasteur's Experiment
Pasteur's experiment confirmed that spontaneous generation does not exist, using a similar technique to that of Spallanzani. He used a curve-necked flask, which did not allow any microorganisms from entering. Over the course of one year, no microorganism spontaneously generated in the flask, but after one day of the neck being broken off, the broth became cloudy with microorganisms. -
(1905) Radiometric Dating
Radiometric dating is a modern technique used to determine the age of something. It looks at how much of a certain substance has decayed, then, in comparing that with the substance's known half-life, can determine the age of the material in question. -
(1920s) Oparin's Hypothesis
Oparin developed, but never tested, the hypothesis that there were gases in the atmospher, such as ammonia, hydrogen gas, and water vapor, which, at high temperatures, could have formed organic compounds. According to Oparin, these compunds would then have been collected in water when the earth cooled. -
(1953) Miller-Urey Experiment
Urey and Miller created an experiment that used gases that Oparin said existed and chemical reactions to produce a variety of organic compunds, including amino acids. This proved Oparin's hypothesis. -
(Mid-1900s) Sidney Fox
Sidney Fox (1912-1998) did extensive research on physical structures, such as microspheres (composed of many protein molecules that are organized as a membrane) and coacervates (collections of droplets composed of lipids, amino acids, and sugars). -
(1980s) Thomas Cech
Cech found that RNA can itself cut strands of RNA, showing that life could have started as RNA. -
(1900s) Lynn Margulis
Margulis developed an endosymbiotic theory, which stated that once one prokaryote engulfed another prokaryote, after millions of years, both would evolve into eukaryotic cells.
