For what reasons is it believed that oxygen was not present when life formed from earth

Explanation:

Why (for what reasons) is it believed that oxygen was not present when life formed on Earth? The life forms were anaerobic, and did not make oxygen. There is a lack of oxidized iron in rocks that are a few billion years old. Eventually oxygen from the oceans moved into the atmosphere, and iron could be oxidized.

is it believed that oxygen was not present when life formed on Earth? The life forms were anaerobic, and did not make oxygen. There is a lack of oxidized iron in rocks that are a few billion years old. Eventually oxygen from the oceans moved into the atmosphere, and iron could be oxidized.

environment controlling gene expression  

Explanation:

Gestational diabetes generally occurs in pregnant women. The sugar level in the bloodstream becomes little high than the normal range during pregnancy. But the glucose level returns to normal after child birth.

The pancreas secrets insulin which helps to lower the blood sugar level in the body. But during pregnancy, the placenta releases some of the hormones which dilutes the effect of insulin. This is known as insulin resistance. So now the pancreas secretes more of insulin to overcome this insulin resistance for the body. Now if a woman during pregnancy does secrete more insulin, the glucose level increases in the body and the woman develops gestational diabetes.

Gestational diabetes greatly depends upon obesity and the ethnicity of the women, but a definite genetic link has not been identified.

This it is a result of the environment control gene expression.