Tsukasa has learned about the cave where the nitric acid is collected. The race is on between Senku and Tsukasa to restore humanity in their respective visions.
The stone age was two million years ago.
.كان العصر الحجري قبل مليوني سنة
Die Steinzeit war vor zwei Millionen Jahren.
L'Età della Pietra è stata due milioni di anni fa,
A idade da pedra foi 
há 2 milhões de anos.
Каменный век был
 два миллиона лет назад.