67 million years ago in the form of phyollths (small sllica flecks in grass that make it difficult to digest)
I think its acid fermentation, but I could be wrong. My class studied this a while ago.
This is referred to as: spontaneous recovery
Spontaneous recovery is a theory of learning and memory which involves unexpected and recurrence of a conditioned response after a period of reduced response or delay. Spontaneous recovery is associated with classical conditioning and operant conditioning. Extinction will happen quickly after a spontaneous recovery, if the conditioned and unconditioned stimulus is not connected.
(of an immature or stem cell) capable of giving rise to several different cell types.
