Masses of gas and dust are pulled together by gravity to form the sun. Remaining dust and debris collides to form other planets.
Formation of Earth (4.6 BYA)
Floating debris in space combines from gravity and massive collisions and begins to form planet Earth. Newborn Earth is completely molten rock.
Cooling of Earth's Surface (4 BYA)
Molten Earth begins to cool and form continental crust due to lack of massive debris collisions on surface.
First Organic Molecules (4 BYA)
First organic molecules form (ammonia, hydrogen gas, water vapor, and methane). Also first types of cells begin to form (anaerobic, heterotrophic, prokaryotes).
Formation of Stromatolites Begins (3.5 BYA)
Cyanobacteria form on upper layers of stromatolites and continually reach top layer of rock as layers add up, thus allowing us to conclude stromatolites are ancient.
Formation of Photosynthetic Life (3 BYA)
First evidence of prokaryotes utilizing photosynthesis to make food.
Earth Resembles Present Day (2.2 BYA)
Photosynthetic organisms begin producing oxygen and Earth begins to resemble its present day form.
Oxygen Levels Equivalent to Today's (2 BYA)
Oxygen (O2) levels reach the same levels they are present in today due to respiration of photosynthetic organisms creating oxygen as a by-product.
Formation of First Eukaryotes (2 BYA - 1.5 BYA)
First eurkaryotic cells formed by prokaryotic cells undergoing endosymbiosis - the process by which an anaerobic prokaryote engulfs an aerobic prokaryote. This mutual relationship offers
Ozone Layer Forms (1 BYA)
Ozone layer forms in atmosphere to protect organism from UV radiation from the sun so they could continue to exist on land.
Use of Microscopes to Discover Microorganisms (circa 1665)
Scientists such as Hooke began to use early forms of microscopes to see microscopic, simple organisms that were vast. They began to conclude that there was a "vital force" in the air that promoted the generation of life such as these organisms.
Redi's Experiment (1668)
Italian scientist Redi conducts experiment in which he puts meat in sealed and open jars and shows that maggots cannot develop on meat unless it is open to flies to lay eggs. He netted two jars with meat which kept flies and eggs off, while the open jars developed flies. This was the beginning of disproving spontaneous generation and the "vital force."
Spallanzani's Experiment (1700s)
Italian scientist Spallanzani conducts experiment showing that boiled meat broth kills off microorganisms and when it is sealed; when sealed it keeps them out and when it is open the broth becomes cloudy with microorganisms. He also aimed to disprove spontaneous generation but people claimed that he boiled the water too long and killed the "vital force" in the air.
Use of Radiometric Dating (Began 1908)
Radiometric dating allows scientists to find how old an object is by analyzing the amount of a certain radioactive substance in the item. Carbon is most often used because once an organism dies it stops taking in carbon-14 so the half-life of the carbon still left can be used to find the age of the organism when it died. For older organisms larger particles are used, such as uranium. In 1908 Ernest Rutherford began to take the first step towards radiometric dating.
Oparin's Hypothesis (1920s)
Scientist Oparin states that the early atmosphere of Earth contained ammonia, hydrogen gas, methane, and water vapor; he hypothesizes that at high temperatures these gases would form simple organic compounds and then undergo complex chemical reactions to form macromolecules such as proteins.
Lynn Margulis and Endosymbiosis (1938)
Scientist Lynn Margulis proposes that early prokaryotic cells formed a "mutually beneficial" relationship known as endosymbiosis during which an anaerobic cell envelopes an aerobic cell. The anaerobic cell provides protection while the aerobic cell provides energy.
Urey and Miller Experiment (1953)
Scientist Urey and graduate student Miller conduct an experiment in which they take the substances Oparin believed were in the early atmosphere and placed them in closed off glass tubes. They then ran an electric current, representing lightning, through the tubes and found that organic molecules began to form.
Sidney M. Fox and Early Cell-like Structures (circa 1960s)
Scientist Fox worked with physical structures that may have preceded to the first cells- microspheres and coacervates. Both grew and could absorb other structures but were not alive because they didn't contain DNA.
Thomas Czech and RNA (1980s)
Scientist Czech finds that a type of RNA that is found in certain eukaryotic organisms is able to act as a chemical catalyst, which is named a ribozyme. This shows that it was possible that early life sprouted from RNA.
Pasteur's Experiment (mid 1800s)
French scientist Pasteur conducts experiment similar to Spallanzani's. He used flasks with curved necks filled with broth and boiled them to kill off any organisms. Then he showed that the broth remained clear for up to a year with the curved neck that kept out microogranisms and when the neck was taken away the broth became cloudy because it was open to microorganisms in the air. This disproved the "vital force" and spontaneous generation.