Tier 7: Pre-Industrial

All Civilization started here. 

Tier 6: Industrial Age

Earth Humans Late 18th Century a.t.b

Tier 5: Atomic Age/Age of Advancement

Earth Humans c. 1940s

Grixian Humans 1781 a.t.b

Tier 4: Space Age

Grixian Humans c. 1800s a.t.b

Tier 3: Space-Faring

Grixians c. 100,000 BC

Grixian Humans 1952 a.t.b

Tier 2: Interstellar

Grixians c. 6000 B.C

Covenant c. 300 B.C

Grixian Humans 1985 a.t.b

Tier 1: World Builder

Pre-Historic Humans c. 150,000 BC

Forerunners c. 150,000 BC