Earth formed around 4.54 billion years ago by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere and then the ocean; but the atmosphere contained almost no oxygen and so would have been toxic to most modern life including humans.
Euthyroid is the state of having normal thyroid gland function. Examples of a nonfunctioning thyroid gland may be hypothyroidism, hyperthyroidism, or thyroiditis.
Hormone: Defined as a water or lipid soluble substance. The endocrine system communicates with nearly 50 million target cells in the body using a chemical language called hormones. A hormone is a chemical, synthesized within an organism, which alters the rate of cellular processes. Types: Steroid.