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- S4.E1 ∙ Hitler's Secret Weapon
- S4.E2 ∙ The Hot Blooded Dinosaurs
- S4.E3 ∙ What Price Coal?
- S4.E4 ∙ The Sunspot Mystery
- S4.E5 ∙ The Plastic Prison
- S4.E6 ∙ Incident at Brown's Ferry
- S4.E7 ∙ Bye Bye Blackbird
- S4.E8 ∙ The Pill for the People
- S4.E9 ∙ The Gene Engineers
- S4.E10 ∙ The Human Animal
- S4.E11 ∙ The Wolf Equation
- S4.E12 ∙ The Dawn of the Solar Age
- S4.E13 ∙ The Business of Extinction
- S4.E14 ∙ The Red Planet
- S4.E15 ∙ Tongues of Men: Part 1
- S4.E16 ∙ Tongues of Man: Part 2
- S4.E17 ∙ Linus Pauling: Crusading Scientist
- S4.E18 ∙ Across the Silent Barrier
- S4.E19 ∙ The New Healers
- S4.E20 ∙ The Green Machine
