-
5 BYA
At this time the solar system began to form. Itconsisted of a swirling mass of gas and dust that began to condense due to gravity. This swirling mass would eventually form the Sun. -
4.6 BYA
Approximately 4.6 billion years ago the sun ignited to enter the stage of developement we still see today. Over the past 400 million years gravity had coerced collisions of large space debris causing planets to form. These collisons were extremely powerful and released large enough amounts of thermal energy to melt large portions of the planet Earth's surface . -
4 BYA
By 4 billion years ago the Earth's moon had formed through a series of collisions similar to the ones that created the planets. At this time it is also acknowledged that the Earth forms a solid crust. Scientists are abel to attain this information through radiometric dating, which determines the age of objects by examining the decay of radioactive isotopes. After the Earth developed a crust it was covered in ocean around 300 million years later. -
4 BYA continued
Also during this time period prokaryotic cells, or cells without nuclei, bein to develope showing the first sign of life on Earth. -
3.5 BYA
This time period represents the begining of marine photisythesis. -
3 BYA
At this time some forms of life are able to perform photosythesis and respiration. -
2.2 BYA
Around 2.2 billion years ago the Earth begins to represent how it looks today. The atmospheric oxygen levels begin to significantly rise. The earliest fossil evidence is from this time. -
2 BYA - 1.5 BYA
During this time period large developements take place as cells with nuclei, or eukaryotes. come to existance. In addition multicellular organisms begin to take shape on Earth. At this time it is believed a small aerobic prokaryote was engulfed by a larger anaerobic eukaryote leading to the theory of endosymboisis which stipulated these two organisms became interdependent and reproduced in the same shape eventually leading to the modern mitochondria in cells. -
1 BYA
1billion years ago marked the formation of the ozone(o3) layer which allowed organisms to exist on land because it protected them from the harmful UV rays of the sun. This time also represents the begining of the proterozoic era. -
Bewtween 1600 and 1700
Francesco Redi performed an experiment at this time to challenge the hypothesis of spontaneous generation. Redi placed two jars with meat on a counter for several days. One jar was left open and the other was covered. At the conclusion of the experiment Redi noticed that larvae had only appeared on the meat in the open jar. Redi stipulated that the larvea did not appear from spontaeous generation but from biogenises. -
Between 1700 and 1800
At this time scientists developed microscropes. These microscopes allowed scientists to view things invisible to the naked eye which was previously impossible. -
Between 1700 and 1800
Lazzaro Spallanzi was a italian scientist that wanted to furthrt Redi's case against the spontanteuos generation hypothesis. At this time scientists still believed microorganisms were a "vital force" in the air. In Spallanzi's experiment he boild two jars of broth and then immediatrly cappe done and left the other open. -
Between 1700 and 1800 continued
At the end of the experiment the open broth was miscolored and the covered broth remained the same. Spallanzi once again emphasized biogenises but opposers argued the seal had actually blocked out the "vital force". -
Between 1800 and 1900
French scientist Louis Pastuer also believed in biogenises and wanted to prove it once and for all. He built off of Spallanzi's broth boiling experiment but to eliminate disbelievers he left broths open but one jar had a curved neck that pointed down. -
Between 1800 and 1900 continued
Pasteur boild the broths and then let them sit. The straight neck jar became miscolored immediatley but the curved neck jar remained the same for one year. To further prove his results Pastuer snapped the neck off the curved jar and the broth became iscolored after one day. This officially proved biogenises to all nonbelievers. -
Between 1900-present (oparin and Haldane) continued
Over time these compound sunderwent complex chemical reactions to form macromolecules which are essential to life. -
Between 1900-present ( Urey And Miller)
Harold Urey and Stanley MIller wanted to deign an experiment that would test Oparins hypothesis which had not been done yet. Urey and Miller designed an apparatus that woould conatin all of the gases mentioned in the hypothesis in a single chamber. This chamber would also be super heated to fuel chemical reactions. The experiment reluted in amino acids as Oparin predicted and proved Oparins hypothesis. -
Between 1900 and present (Cech)
Tomas Cech found a type of Rna in some unicellular eukaryotes that was able to act as a chemical catalyst. Cech called this type of RNA molecule a ribosome. Later findings showed ribosomes could act as catalysts in their own replication. These findings supported the hypothesis that life could have started with self-replicating molecules of RNA. -
Between 1900- present (Fox)
Sydney Fox performed extensive research on the physical structures that may have led to the first cells. Two structures found that could hav egiven rise to cells are microspheres and coacervates. THis is significant because for many years it was believed that all cell structures and chemical reactions required enzymes, but these two structures were able to form spontaneously under certain conditions. -
Bewtween 1900- present (Margulis)
Lynn Margulis created a hypothesis on how the eukaryotic cells may have developed a beneficial relationship with prokaryotic cells as they evolved. The hypothesis stipulates that a large eukaryote engulfed a smaller prokaryote and the two became interdependent. As the organism reproduced the beneficial situation spread and it eventually evolved into the mitochondria of modern day cells. This is called the theory of endosymboisis. -
Between 1900- present ( Oparin and Haldane)
Alexander Oparin and John Haldane forned a hyphothesis that explained the begining of life on Earth. They believed that the early Earth atmosphere contained a diverse mixture of gases. They said that extreme temperatures in the atmosphere cause these gases to react and form compounds such as amino acids. Once the Earth cooled and the water vapor in the air condensed to form lakes and seas these simple organic compounds collected in the water.
