How are triads represented in sheet music? What are chord progressions?

In tonal Western classical music (music with a tonic key or "home key"), the most frequently encountered chords are triads, so called because they consist of three distinct notes: the root note, and intervals of a third and a fifth above the root note. ... A series of chords is called a chord progression

The period that marks the paleolithic era is between the 250,000 to 10,000 years.

Answerthe third and fourth;