1. The eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago
   - Precambrian, Precambrian aeon, Precambrian period

Type of: aeon, eon

• family Typhlopidae
• family Tytonidae
• family Uintatheriidae
• family Ulmaceae
• family Ulvaceae
• family Umbelliferae
• family Unionidae
• family unit
• family Upupidae
• family Uranoscopidae
• family Ursidae
• family Urticaceae
• family Usneaceae
• family Ustilaginaceae
• family Valerianaceae
• family Varanidae
• family Veneridae
• family Verbenaceae
• family Vespertilionidae
• family Vespidae
• family Violaceae
• family Viperidae
• family Vireonidae
• family Viscaceae
• family Vitaceae