-
(5BYA) Sun Formed
5 billion years ago, our solar system was a swirling mass of gas and dust. Gravity pulled this debris together forming the sun, Then the other gas and dust then circled the sun. This marks the beginning of astronomical development in our solar system. All of this has been evidenced by computer models. -
(4.6 BYA) Earth Formed
According to computer models, this date marks the beginning of our planet. Earth was built from matter that its gravitational forces gradually pulled in, accumulating more and more mass over a 400 million-year period. Collisions between Earth and debris also melted portions of the Earth's surface. -
(4BYA) Organic Molecules
By studying the age of the oldest unmelted surface rock, scientists have found rocks and crystals about 4 billion years old. This allows them to infer organic molecules began to accumulate about 4 billion years ago, a first on planet Earth. -
(4BYA) Life on Earth
Archaeal species that produce methane during metabolism are similar to the cellular life that first populated earth about 4 billion years ago. This represents the first sign of life on Earth, discovered through usage of computers and examining species such as Archea. -
(3.5 BYA) Stromatolites/ Radiometric Dating
Lynbgya cells often grow in colonies and thus form latered structures called stromatolites. Some as old as 3.5BYA have been found. Lynbgya represent a genus of cyanobacteria which mean they were one of the first unicellular prokaryotes to inhabit the Earth. These Lynbgya were most likely dated by radiometric dating, a process which takes into accound an element's half-life (time it takes for half of the element's isotopes to decay) and calculate the object's age. -
(3 BYA) Photosynthesis
Some forms of life had already become photosynthetic by this time. This has been inferred by a variety of geologic evidence, like chemical traces of photosynthetic activity. This represents a first on planet Earth and these photosynthetic organisms helped allow for the development of many other life forms. -
(2.2BYA) Earth Formalized
Volcanoes have emitted gas in the preceeding years forming an atmosphere and Earth's formation ceases around 2.2 billion years ago. It is left looking similar to today. Computer models tell us this, and this matters because it marks the completion of the creation of Earth. -
(2 BYA) Oxygen Levels of Today
2BYA marks the finalizing of today's oxygen levels. Scientists can study this through chemical analysis. These oxygen levels are what allowed species to thrive. -
(1.5BYA) Endosymbiosis
It is theorized by Margulis and supported by a large body of evidence that a small type of aerobic prokaryote was eaten by and thrived in a larger, anerobic prokaryote (called endosymbiosis). This allowed for the eukaryotes to provide a beneficial environment, and the prokaryotes to provide a method of energy synthesis. -
(1BYA) Ozone
After oxygen levels reached those of today, the gas reached the upper part of the atmosphere where it was bombarded with sunlight. This caused atoms to break apart (into two oxygen atoms) and resulted in the formation of ozone (three oxygen molecules). This poisonous gas protects Earth from the damaging ultraviolet rays of the sun. They allow for life to exist on Earth. -
Spallanzi's Experiment
Lazarro Spallanzi's tested the hypothesis of spontaneous generation of microorganisms. He proved his hypothesis that microogranisms formed not from air but from other microorganisms by boiling broth in open and sealed flasks. The ones that were sealed remained clear proving the 'vital force' wrong, yet others argued he had killed the 'vital force' and the ideas of spontaneous generation remained alive for another century. -
Redi's Experiment/ First Microscopes
The first microscope was invented by Robert Hooke to examine plant cells in 1665. Through the use of optical lenses to magnify objects. Sceintists then used this to discover the world was teeming with microorganisms. Francesco Redi conducted an experiment in 1668 to test his hypothesis that meat kept away from adult flies would remain free of maggots. His experiment showed (since the uncovered ones had maggots) that flies only come from eggs from other flies, disproving spontaneous generation. -
Pasteur's Experiment
Louis Pasteur sought to conclusively disprove spontaneous generation. He made a curved neck flask to allow air inside a flask to mix with air outside of flask. This prevented microorganisms from entering flask. Boiled broth stayed clear for a year, and when flask was broken it became contaminated within a day. Spontaneous generation, while still a belief held on to by some after Spallanzi's experiment, was officialy denied, paving way for new theories of organisms' development to come about. -
Oparin's Hypothesis
Oparin and Haldane thought the atmoshpere contained ammonia early on with other gasses forming organic compunds at high temperatures. These compounds then would become macromolecules essential for life (like proteins). If true, it would explain the origins of these macromolecules. -
Urey and Miller
Since Oparin never tested his hypothesis, Miller and professor Urey set up an experiment in 1953. The experiment had a chamber with the gases and electric sparks created energy to drive chemical reactions. They found the hypothesis was true and the result was organic compounds and amino acids were included. This showed the origins of these organic compounds, a huge step in understanding the development of life. -
Lynn Margulis
Born 1938, Lynn Margulis proposed early cells developed a mutually beneficial relationship. He explained the theory of embosymbiosis in which a small aerobic provides energy to a larger anaerobic eukaryote that 'swalloed' it.The eukaryotes then made a beneficial environment and the prokaryotes provided a method of getting energy. This helped further our understanding of evolution greatly. -
Sidney Fox
Sidney Fox, along with many other scientists, have done extensive research on the physical structures that could have brought about the first cells. The theory is that microspheres (composed of protein molecules) are organized as a membrane and coacervates (collections of droplets) are composed of molecules of lipids, amino acids, and sugars. This helps expain where cells came from and move our understanding of evolution forward. -
Thomas Cech
In the early 1980s. Cech found that some unicellular eukaryotes have a type of RNA able to act as a chemical catalyst, similar to an enzyme. He used the term ribozyme for an RNA molecule like this. He figured this out through labratory examination of eukaryotes and it helped advance our knowledge on how enzymes came about.
