The neurotransmitters and are responsible for mood, attentiveness level, and other psychological states

The answer to your question is Dopamine and Serotonin. Dopamine is a neurotransmitter that affects our focus, drive, attention, memory and clear thinking. Elevation of dopamine levels leads to improvement in our mood, alertness, and libido. Serotonin, on the other hand, helps regulate a wide range of psychological and biological functions. It regulates psychological functions such as mood, anxiety, arousal, aggression, impulse control and thinking abilities. 

which

what is a measurement of the earth’s history divided into time periods?

> fossil record <

sedimentary rock

> geologic time scale <

radioactive elements