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Greatest Discoveries, Inventions or Scientific work:
The Planets Move (2000 B.C. - 500 B.C.)
The Earth Moves (1543) Nicolaus Copernicus
Microorganisms (1674) Anton Van Leeuwenhoek, lens grinder
The Cell Nucleus (1831) Robert Brown
Oxygen (1770s)
The nature of elements (1770s) Antoine Lavoisier 
Atomic Theory (1808) John Dalton (English)
Continental Drift (1911) Alfred Wegener 
K-T Asteroid Theory of Dinosaur Extinction (1980) Walter Alvarez
Classification of Species (1735) Carl Linnaeus
Rules of Heredity (1850s) Gregor Mendel
Human Anatomy (1538) Andreas Vesalius
Genes Are Located on Chromosomes (1910 - 1920s) Thomas Hunt Morgan
DNA Is the Genetic Material (1928, 1944, 1952) Oswald Avery, Linus Pauling
DNA Is a Double Helix (1953) James Watson and Francis Crick
Blood Circulation (1628) William Harvey
The Law of Falling Bodies (1604) Galileo Galilei 
Universal Gravitation (1666) Isaac Newton
Laws of Motion (1687) Isaac Newton
The Second Law of Thermodynamics (1824 - 1850)
The Quantum Leap (1900 - 1935) Max Planck, Albert Einstein,
                            Werner Heisenberg and Erwin Schrodinger.
                            
Inventions:
Printing Press
Harnesing electricity
Fire 800,000 years ago
The wheel 4,000 BC
Written Language
Vaccines
Accidental Inventions:
Many of our most important innovations and inventions have been accidents which occurred in the pursuit of some other objective upon which observant scientists and engineers followed up.
Penicillin
Bacteriologist Alexander Fleming working at St. Mary's Hospital in London in 1928. He observed that a plate culture of Staphylococcus had been contaminated by a blue-green mold and that colonies of bacteria adjacent to the mold were being dissolved. Curious, Alexander Fleming grew the mold in a pure culture and found that it produced a substance that killed a number of disease-causing bacteria. Naming the substance penicillin, Dr. Fleming in 1929 published the results of his investigations, noting that his discovery might have therapeutic value if it could be produced in quantity.
Radioactivity
Physicist Henri Becquerel ran a series of experiments to see if naturally fluorescent minerals produced X-rays after they had been left out in the sun. There was one week with a long stretch of overcast skies. He left his equipment wrapped up together in a drawer and waited for a sunny day. When he got back to work, Becquerel realized that the uranium rock he had left in the drawer had imprinted itself on a photographic plate without being exposed to sunlight first.
Post-It Notes
Spencer Silver created an extremely weak adhesive while working for 3M. For five years, Silver promoted his invention within 3M, both informally and through seminars, but without much success. In 1974, a colleague of his, Art Fry, who had attended one of Silver's seminars, came up with the idea of using the adhesive to anchor his bookmark in his hymnbook. The idea of post-Its was born.
Coca-Cola
It was originally meant as a miracle tonic for treating hangovers, but a batch was made using carbonated water instead of plain water, leading to this popular beverage.
Vulcanization
Goodyear accidentally dropped a glob of rubber-sulfur solution on a hot plate, and was surprised that this process made the rubber firm and flexible, not shattering in cold temperatures.
Pacemaker
While working on a device to record heart sounds, American engineer Wilson Greatbatch inserted the wrong resistor into the circuit, causing it to repeatedly pulse on for 1.8 milliseconds, then off for 1 second.
Google
"It wasn't that we intended to build a search engine. We built a ranking system to deal with annotations," said Larry Page.
Racing car ground effects
Colin Chapman, founder of Formula One Lotus asked his engineer Peter Wright to develop a side pod which conditioned the radiator without drag. Wright produced a design with aircraft style ducts to get thrust to offset drag and noticed in wind tunnel tests that downforce was increased. UC Berkeley and MIT professor, Shawn Buckley, who had designed a high wing for indy cars in the 60's and worked with Chapman on undercar aerodynamics worked with them to produce a car with increased downforce, improving cornering. The team won 5 races that year, and 2 in 1978 while they developed the much improved Lotus 79.
In a 2010 interviews with Formula 1 engineers, the Lotus 78-79 was considered the most innovative car to date.
Yellow tennis balls
In 1964 I was taking a tennis class at UC Davis and we had to mark the balls we brought to class so we could get them back at the end of the class. We were dying t-shirts yellow for our intramural softball team so I threw my tennis balls in, figuring yellow was easier to see. The instructor said they were distracting and I had to bring white balls the next class. I should have patented the idea. Yellow balls were officially introduced in 1972, because they were more visible on television. I never got credit for it and couldn't find who did.
In 1975 I bought some balls on sale at my local sporting goods store and it turned they were white. My opponent on the company tennis ladder refused to play with them.
See:
Failure - Persistence - Success
Eureka!
Top 10 Accidental Inventions: JUNKies: Science Channel
Links:
American Inovation
100 Greatest Discoveries
Most Important Inventions, NY Times
last updated 16 Mar 2009