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(5 BYA) Formation of Solar System
The solar system started to form from masses of gas and dust. Over time, gravity pulled the debris together to form the sun. The remaining debris collided to form planets. -
(4.6 BYA) Formation of Earth
Earth began to form by colliding with the space debris surrounding the sun. The collisions between earth and space released a high amount of thermal energy. Sometimes these collisions melted large portions of the earth. -
(4 BYA) Formation of Organic Molecules
The oldest known rocks and crystals are from 4 billion years ago, so it was inferred that organic molecules began to accumulate 4 billion years ago. This was discovered using radiometric dating. picture: Amino Acid -
(4 BYA) Life Forms/ Archaea
Archaea, a group of unicellular organisms, lived 4 billion years ago. -
(3.5 BYA) Existence of Stromatolites
Lygnbya, a genus of today's cyanobacteria, grow into colonies and form layered structures called stromatolites. Fossils of stromatolites from 3.5 billion years ago are known. -
(3 BYA) Photosynthetic Life
Some forms of life had become photosynthetic. Scientists infer this by studying chemical traces of photosynthesis, and by using other evidence. -
(2.2 BYA) Earth
Earth looks very similar to today’s earth. -
(2 BYA) Oxygen Levels
O2 reached today's levels. -
(2 BYA- 1.5 BYA) Endosymbiosis
The first endosymbiotic life forms existed at this time. This is when an aerobic prokaryote lives inside a larger, anaerobic prokaryote and provides it with energy. It is a mutually beneficial relationship. These are the first ancestors of today’s eukaryotes. -
(1 BYA) Fomation of Ozone Layer
Ozone (O3) formed and protected organisms from harmful UV rays so they could exist on land. -
(1665) Robert Hooke and the Microscope
Robert Hooke studied nature using a light microscope, which uses optical lenses to magnify objects by bending light rays. He discovered cells by observing a piece of cork. Microscopes are used to study tiny organisms. -
(1668) Francesco Redi's experiment
Francesco Redi studied the development of flies. He set up an experiment with jars that had meat inside. Those that were uncovered (and exposed to adult flies) grew maggots, and those that were covered with a net remained free of maggots. His observation disproved the belief that flies were spontaneously generated from the meat, and that they came from other flies instead. -
(1700s) Lazzaro Spallazani 's Experiment
Lazzaro Spallanzani challenged the theory of spontaneous generation in microorganisms. He observed that microorganisms didn’t grow in meat broth if the container was sealed from other microorganisms present in the air. Many were not persuaded by his experiment, arguing that sealing the containers prevented the “vital force” required in air to allow microorganisms to generate. -
(1900s) Radiometric dating
Radiometric dating is used to figure out how old materials are by measuring the quantity of their radioactive isotopes (atoms with extra neutrons and unstable nuclei). Throughout the years, the amount of the radioactive isotope present in a material decreases at a constant exponential rate, called its half-life. To determine the age, the quantity of the radioactive material left over after decay is compared with that of another substance whose amount stays constant. -
(1920s) Oparin's Hypothesis
Oparin thought that the early atmosphere contained ammonia, hydrogen gas, water vapor, and hydrocarbon compounds. He believed that the gases formed simple organic compounds at high temperatures. He also thought that the organic compounds collected in water and went through chemical reactions that produced the macromolecules essential to life. -
(1912-1998) Sidney Fox
He studied physical structures that are believed to have given rise to the first cells. Examples of these structures are microspheres, which are composed of proteins organized as a membrane, and coacervates, which are groups of droplets consisting of lipids, amino acids, and sugars. -
(1960s) Lynn Margulis
Lynn Margulis studied cell structure. She noticed that the mitochondria and chloroplasts in cells looked remarkably similar to bacteria. She was convinced that the eukaryotic cells we know today arose from the process of endosymbiosis. This occurs when anaerobic cells engulf aerobic cells, resulting in a mutually beneficial relationship. -
(1980s) Thomas Cech
He learned that a certain type of RNA found in unicellular eukaryotes acts like a catalyst (similar to an enzyme), which promotes a specific chemical reaction. He called it a ribozyme. Other studies used his discovery and found out that ribozymes and other forms of RNA can self-replicate. -
(mid-1800s) Louis Pasteur's Experiment
Louis Pasteur disproved the theory of spontaneous generation of microorganisms once and for all by performing an experiment similar to Spallazani’s. It showed that microoganisms were carried in the air. However, his experiment allowed air (the vital force), but not other microorganisms, to enter flasks, which cleared up any controversy. -
(1953) Miller and Urey Experiment
Stanley L. Miller and Harold C. Urey set up an experiment to test Alexander Oparin's hypothesis. They simulated reactions between the gases Oparin believed where in the atmosphere and electric sparks. Their experiment resulted in an assortment of organic compounds.
