The solar system was formed by a swirling mass of gas and dust. A few million years later the sun was also formed by dust and gas pulled together by gravity. During this time, the earth and planets contained water vapor and gases, such as Carbon, but no oxygen.
(4.6 BYA) Earth Formed
The earth was formed by the gravitational pull colliding with space debris. Scientists use radiometric dating to establish the age of the earth through sedimentary rocks. This affected the gravitational pull because it circles around the sun and began life on earth.
(4 BYA) Crystals and Other Minerals Formed
The oldest known rocks and crystals are formed four billion years ago. Scientists estimate the earth's age by using a dating method that is based on the decay of Uranium and Thorium isotopes in rock crystals. Collisions between earth and large pieces debris probably caused the surface of the earth to melt many times as the planet was formed. The age of the oldest unmelted surface rock (crystals) tells us when these collisions stopped and the cooling of the earth's surface began.
(4 BYA) Organic Molecules Formed
Scientists infer that organic molecules began to accumulate four billion years ago. All of the elements found in organic compounds are thought to have existed on earth and in the rest of the solar system, when the earth formed. Oparin & Haldane tried to solve the problem of how & where these elements assembled into organic compounds. Scientists say that organic compounds could have been carried to earth by debris from space; some were found in a fallen meteorite. The first were CO2 & H20 Vapor.
(3.5 BYA) Stromatolite Fossils Formed
Fossils of stromatolites are as old as 3.5 billion years. Fossils are formed by layers of sedimentary rock building upon layers. Because the land was once covered with water, dirt settled, over time, fossils were created.
(3 BYA) Some Life Became Photosynthetic
Some forms of life had become photosynthetic by 3 million years ago. Oxygen produced by photosynthesis was harmful to anaerobic cells and caused the ozone layer to form. It allowed anaerobic respiration to use oxygen so it would not be harmful to the cells. Scientists infer this from a variety of geological evidence, such as chemical traces of photosynthetic activity. Oxygen (a byproduct) was damaging to many early unicellular organisms.
(2.2 BYA) Earth Looks Like It Does Today
This is when the Earth began to look much like it does today. During this time period, the Earth started to be able to support life, such as plants and organisms.
(2 BYA) Oxygen Levels Reached Today's Levels
Oxygen levels reached today’s levels. Oxygen bonded to other compounds during this time. This was one of the first steps in aerobic respiration. By having oxygen, plants, animals, humans, and all types of life started to evolve and replicate. Many scientists believe that it took more than a billion years (approx. 2 BYA) for oxygen gas levels to reach today's.
(2-1.5 BYA) Aerobic Prokaryotes Began to Live in Anaerobic Prokaryote
A small aerobic prokaryote was engulfed and began to live and replicate inside of a larger anaerobic prokayote. This theory is called endosymbiosis. The eukaryotics provided a beneficial environment and the prokayotics provided a method of energy synthesis. Scientists infer that endosymbiotic aerobic prokaryotes evolve into modern mitochondria.
(1 BYA) Ozone (O3) formed
Ozone (O3) formed which protected organisms from harmful UV rays so they could exist on land. Many scientists think that it took a billion years or more for oxygen gas levels to reach today's levels. Oxygen gas reached the atomsphere, where it bombarded with sunlight. Some wavelenghts of sunlight can split O2 to form O atoms. These O atoms react with O2 and form the ozone, which absorbs ultraviolet radiation. Without the protection of the ozone layer, life could not extist because it damages DNA
(1626-1697) Redi's Experiment & the First Microscope
(1626-1697) During Redi's experiment, he noticed and observed the cycle of flies and that maggots appear where ever flies land. He questioned the belief that came from rotten meat. To test this, he conducted an experiment. He found that maggots were only in open jars with rotten meat, not closed jars.
Also during this time period, scientists use the first microscope to discover microorganisms. Robert Hook was the first to use a light microscope that used optical lenses to magnify organisms.
(1729-1799) Spallanzani’s experiment
(1729-1799) Spallanzani’s experiment was testing the hypothesis the of generation of microorganisms. His hypothesis was as follows: microorganisms were not found in air, but come from other microorganisms. He concluded that an open flask’s broth became cloudy, but the closed flask's broth was not contaminated.
(1822-1895) Pasteur's Experiment
Pasteur's experiment was similar to Spallanzani's & Redi's, but he changed his flasks. He used curved or "gooseneck" flasks to keep the dust and dirt from contaiminating his experiment. Instead, the dirt settled in the "neck" of the flasks. He boiled broth in two flasks for an extensive amount of time. His conclusion was that the broth was only contaminated with microorganisms when curved necks were removed from flask, besides that, they didn't contain any.
(1980s) Thomas Cech's Experiment
(1980s) Thomas Cech's concluded that a type of RNA is able to act as a chemical catalyst (Ribozyme). These ribozymes act as catalysts for their own replication
(1894-1980) Oparin's Hypothesis
(1894-1980) Oparin’s hypothesis stated the following: early atmosphere contained ammonia, hydrogen gas, water vapor, hydrogen and carbon compounds. If the temperature is raised, these gases might form organic compounds, such as amino acids.
(1893-1981) Urey & (1930-) Miller's Experiment
(1893-1981) Urey & (1930-) Miller set up an experiment using Oparin’s hypothesis, which stated that simple organic molecules containing carbon were formed.To prove his theory, these two scientists mixed water vapor and ammonia, methane and hydrogen gases. They found that three amino acids were sythesized. This was an important milestone in this type of investigation and was a great excitement above evolutionists.
(1912-1998) Sidney Fox Experiment
Sidney Fox conducted research on physical structures that may have been in first cells. These structures were called microspheres. By combining purified amino acids and heating them in a waterless environment, he observed that there were no proteins aquired. However, his experiment showed that amino acids could also have formed, not only proteins.
(1938-) Lynn Margulis
(1938-) Lynn Margulis stated that prokaryotic cells may have developed a mutually beneficial relationship. He created the theory Endosymbiosis. This stated that a small aerobic prokaryote was engulfed by and began to live and reproduce inside a larger anaerobic prokaryote.