Brahmagupta (7th century) formalized the rules for zero and negative numbers, laying the foundation of modern mathematics.

The Rosetta Stone contained inscriptions in three scripts, allowing scholars to unlock Egyptian hieroglyphs for the first time.

Karl Marx wrote *Das Kapital* (1867), a critique of capitalism, laying foundations for Marxist economic and political theory.

The Peace of Westphalia (1648) concluded the Thirty Years' War and established principles of sovereign states and non-intervention.

Sulfur dioxide emitted from fossil fuel combustion oxidizes to sulfuric acid in the atmosphere, contributing to acid rain.

The Schengen Agreement allows passport-free travel across many European countries, facilitating movement and integration in the EU.

Orville and Wilbur Wright achieved the first powered flight on December 17, 1903, at Kitty Hawk, North Carolina.

Silver has the highest electrical conductivity of all elements, making it ideal for electronics, though copper is more widely used.

Copper was the first metal widely used by humans in the Chalcolithic period, preceding the Bronze Age when alloys were developed.

Ferdinand Magellan led the first expedition to circumnavigate the globe (1519–1522); although he died en route, the voyage completed the circuit.