The Pacific Ocean is the largest ocean in the world at 155,557,000 sq km.   The Atlantic Ocean is the second largest ocean in the world at 76,762,000 sq km.
The cause of major depressive disorder is a combination of brain chemistry, family history, and psychosocial environment. It is not certain which of these factors dominates, but abnormal levels of the neurotransmitters norepinephrine, serotonin, and dopamine are closely linked with depression.
Credit: littleny | Shutterstock. Depression, or major depressive disorder, is a mental health condition marked by an extended sense of sadness and despair that affects how a person thinks, feels and functions. The condition may significantly interfere with a person's daily life and may prompt thoughts of suicide.