1632 – 1723: Antonie van Leeuwenhoek teaches himself to grind lenses, builds a microscope and draws protozoa, such as Vorticella from rain water, and bacteria from his own mouth.
1665: Robert Hooke discovers cells in cork, then in living plant tissue using an early microscope.
1839: Theodor Schwann and Matthias Jakob Schleiden elucidate the principle that plants and animals are made of cells, concluding that cells are a common unit of structure and development, and thus founding the cell theory.
The belief that life forms are able to occur spontaneously (generatio spontanea) is contradicted by Louis Pasteur (1822 – 1895) (although Francesco Redi had performed an experiment in 1668 that suggested the same conclusion).
1855: Rudolph Virchow states that cells always emerge from cell divisions (omnis cellula ex cellula).
1931: Ernst Ruska builds first transmission electron microscope (TEM) at the University of Berlin. By 1935, he has built an EM with twice the resolution of a light microscope, revealing previously-unresolvable organelles.
1953: Watson and Crick made their first announcement on the double-helix structure for DNA on February 28.
1981: Lynn Margulis published Symbiosis in Cell Evolution detailing the endosymbiotic theory.