Thank you for the question on the Great Flood of Genesis, “According to Genesis, did God destroy all life on Earth or just mankind during the Great Flood?”
Genesis 6 says this, “The LORD regretted that he had made human beings on the earth, and his heart was deeply troubled. 7 So the LORD said, “I will wipe from the face of the earth the human race I have created—and with them the animals, the birds and the creatures that move along the ground—for I regret that I have made them.” 8 But Noah found favor in the eyes of the LORD” (NIV).
God declared that he will destroy all animals, birds, and creatures that move along the earth. As God surveyed the people of the earth, Noah found favor with God and extended that grace to his family of his wife and his three children and their spouses. In the provision of Noah and his family, God also extended that grace by saving two of each kind of land animals aboard the ark.
Summary: God spared two of each kind of land creatures and 8 humans aboard the ark that Noah and his family made. The sea creatures were not completely exterminated from the ocean.
-Kingston