When each idea was found

Courses teach the ideas in a tidy order. People found them in a messy one: gold was known long before anyone knew what an element was, and a Babylonian scribe used Pythagoras' theorem over a thousand years before Pythagoras.

4500 BC · Chemistry

Gold · Oldest known gold jewellery: Varna, Bulgaria, about 4500 BC · symbol from Latin aurum

1800 BC · Math

Pythagoras' theorem · Babylon, about 1800 BC · proved by Greeks about 500 BC

1650 BC · Math

The π Mystery · Egypt and Babylon, about 1650 BC · pinned down by Archimedes, about 250 BC

250 BC · Chemistry

Density · Archimedes, about 250 BC

14 · Math

Percent change · Roman taxes, about AD 14 (per centum = per hundred)

1687 · Physics

Newton's second law · Isaac Newton, 1687

1772 · Chemistry

Oxygen · Carl Wilhelm Scheele (Sweden), about 1772

1779 · Biology

Photosynthesis · Jan Ingenhousz showed light is needed, 1779

1827 · Physics

Ohm's law · Georg Ohm, 1827

1847 · Physics

Energy conservation · Mayer, Joule and Helmholtz, 1840s

1953 · Biology

DNA · Structure: Franklin, Watson, Crick and Wilkins, 1953