- L: Earth is Formed (Precambrian)
- P: Photosynthetic bacteria add oxygen to the atmosphere (Precambrian)
- H: Simple bacteria, the earliest forms of life appear (Precambrian)
- C: Earliest Dinosaurs and mammals appear (Triassic)
- F: Mass extinction at the end of the period kills all dinosaurs (Cretaceous)
- M: Mammoths and Mastodons (Quaternary)
- N: Dinosaurs are Dominant (Jurassic)
- O: First Land Plants (Ordovician)
- J: Gymnosperms (seed plants) dominate (Permian)
- K: Rise of invertebrates, corals, worms, and trilobites (Cambrian)
- A: First Modern Humans (Quaternary)
- B: Insects Appear (Devonian)
- D: Single-celled organisms like cyanobacteria (Precambrian)
- E: Early Tropical Forests Cover Earth (Carboniferous)
- G: Early Fish Evolve (Silurian)
- I: Placental Mammals Evolve (Tertiary)
Parent Tip: Review the logic above to help your child master the concept of earth history worksheet.
