Oil floats on water because it is less dense.

Pictures were resized to fit. Nothing else was changed.

• Charles Darwin. Julia Margaret Cameron. Public domain.
• Jane Goodall. U.S. Department of State. Public domain.
• George Washington Carver. Public domain. Restored by Adam Cuerden.
• Barbara McClintock in her laboratory. Smithsonian Institution. Public domain.
• Ernest Everett Just. Public domain.
• Wangari Maathai. Kingkongphoto. CC BY-SA 2.0.
• Marie Curie. Henri Manuel. Public domain.
• Rosalind Franklin at a microscope. MRC Laboratory of Molecular Biology. CC BY-SA 4.0.
• Percy Julian. Public domain.
• Tu Youyou. Bengt Nyman. CC BY-SA 4.0.
• Dmitri Mendeleev. Public domain.
• Alice Ball. Public domain.
• Isaac Newton. Godfrey Kneller. Public domain.
• Michael Faraday. Public domain.
• Chien-Shiung Wu. Smithsonian Institution. Public domain.
• Ada Lovelace. Alfred Edward Chalon. Public domain.
• Shirley Ann Jackson. World Economic Forum / Qilai Shen. CC BY-SA 2.0.
• A later drawing of Hasan Ibn al-Haytham. Public domain.
• Mary Anning. Painting credited to Mr. Grey. Public domain.
• Katherine Johnson. NASA. Public domain. Restored by Adam Cuerden.
• Mae Jemison. NASA. Public domain.
• Nicolaus Copernicus. Public domain.
• Galileo Galilei. Justus Sustermans. Public domain.
• A wood frog. The Cosmonaut. CC BY-SA 2.5.
• A honey bee on a flower. Tanner Smida. CC BY 4.0.
• A button mushroom. chris_73. CC BY-SA 3.0.
• A chimpanzee in a forest. Giles Laurent. CC BY-SA 4.0.
• Rainforest canopy in the Amazon. CIAT. CC BY-SA 2.0.
• Sweet wormwood, the plant artemisinin comes from. Kristian Peters. CC BY-SA 3.0.
• A university science building. Mike Peel. CC BY-SA 4.0.
• A magnet pulling a piece of magnetite. GOKLuLe. CC BY-SA 3.0.
• Earth, photographed from Apollo 17. NASA. Public domain.
• Jupiter's clouds, from NASA's Juno spacecraft. NASA / JPL-Caltech / SwRI / MSSS. Public domain.
• The Hubble Space Telescope above Earth. NASA. Public domain.
• Telescope domes on Mauna Kea. T. Wynne / NASA JPL. Public domain.
• Hands being washed with soap. Lars Klintwall Malmqvist. Public domain.
• A common octopus. Albert Kok. CC BY-SA 3.0.
• Stonehenge, an old stone circle used to track the sky. garethwiscombe. CC BY 2.0.
• A microscope on a bright table. Ann 2000. CC BY-SA 4.0.
• A lab dish with spots of germs. SS. Antonio e Biagio e Cesare Arrigo. CC BY-SA 4.0.
• The Wright Flyer on its first flight in 1903. John T. Daniels. Public domain.
• Part of Babbage's Difference Engine. geni. CC BY-SA 4.0.
• Lyme Regis, England, beside the sea cliffs. Eugene Birchall. CC BY-SA 2.0.
• St Mary's Hospital in London. Enric. CC BY-SA 2.0.