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(5BYA) The Solar System
The solar system was a mass of swirling gas and dust. Over time, gravity pulled the materials together to form the sun. This resulted in the sun becoming the center of the solar system. -
(5BYA) Planets
Scientists believe that the planets formed at this time through repeated collisions of space debris. -
(4.6BYA) Formation of Planet Earth
Earth became larger as gravity pulled more debris together. This was the beginning of the formation of the Earth we know today. -
(4.6BYA) Space Collisions
Collisions between space debris and Earth released large amounts of thermal energy, sometimes melting large portions of the Earth's surface. -
(4BYA) Planet Earth
The Earth is estimated to be four billions years old. This was determined by studying layers of sedimentary rock. -
(4BYA) The First Cells
Little or no oxygen existed on Earth. Therefore, the first cells are predicted to be anaroebic, heterotrophic prokaryotes that ate organic molecules. -
(3.5BYA) Stromalites
Stromalites were discovered. Stromalites are layered structures that form from colonies of cells. -
(3BYA) Photosynthetic Life
Some forms of life became photosynthetic. Scientists infer this because of chemical evidence of photosynthetic activity. -
(2.2BYA) Earth
Earth bagan to look like the Earth of today. -
(2BYA) Oxygen Levels
Oxygen levels reached the levels that they are today. -
(1.5BYA) Endosymbiosis
A theory suggests that a type of small aerobic prokaryote was swallowed by a larger anarerobic prokaryote and began to live inside the bigger cell at this time. Then, it was inferred that the small prokaryote evolved into the modern mitochondria. This theory is called endosymbiosis. -
(1BYA) Ozone Layer
The ozone (O3) formed. This protected organisms from harmful UV rays so they could exist on land. -
(1600-1700) Francesco Redi
Francesco Redi noticed the different developmental stages of flies. Redi preformed an experiment and discovered that the theory of spontaneous regeneration is false. -
(1600-1700) Microscope
Microscopes began to be used for scientific research. -
(1700-1800) Spallanzani
Lazzaro Spallanzani performed an experiment, hypothesizing that microorganisms come from other microorganisms (biogenesis). -
(1900-present) Urey-Miller Experiement
Stanley L. Miller and Harold C. Urey preformed an experiment using Oparin’s hypothesis that Earth’s gases would form simple organic compounds at high temperatures. They performed this experiment by putting the specific gases in a chamber and using electric sparks to drive the chemical reactions. It resulted in organic molecules forming, which proved Oparin's hypothesis. -
(1800-1900) Louis Pasteur
Louis Pasteur cleared up the controversy of spontaneous generation by performing an experiment. He won a prize from the Paris Academy of Science. -
(1900-present) Lynn Margulis
Lynn Margulis developed the theory of endosymbiosis, which theorized that early prokaryotic cells had a mutual relationship. -
(1900-present) Thomas Cech
Thomas Cech discovered a kind of RNA in unicellular eukaryotes that acts as a catalyst. He referred to it as a ribozyme. -
(1900-present) Oparin and Haldane
Scientists Alexander I. Oparin and John B. S. Haldane hypothesised that the early atmosphere contained ammonia, hydrogen gas, water vapor, and carbon compounds and these gases formed organic compounds at high temperatures. -
(1900-present) Sidney Fox
Sidney Fox did extensive research on cell structure. This included studying microspheres and coacervates. -
(1900-present) Radiometric Dating
Radiometric dating began to be used. This is a method of determining the age of various materials. This is completed by measuring the quantity of a specific radioactive isotope in an object.
