These nouns refer to something that takes place or comes to pass. Occurrence and happening are the most general an everyday occurrence; a happening of no great importance. Event usually signifies a notable occurrence: worldevents reported on the evening news. "Great events make me quiet and calm; it is only trifles that irritate my nerves".
Very few metals can resist natural weathering processes like oxidation, which is why generally only the less reactive metals, such as gold and platinum, are found as native metals.
Native metals were prehistoric man's only access to metal, because smelting is thought to have been discovered around 6500 BC.Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics.
The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable color and luster. Metals are often extracted from the Earth by means of mining, resulting in ores that are relatively rich sources of the requisite elements.