Why believe the bible?

[Angrboda]

The notion that adam, man, created in the image of God, is also Adam, the first man with a soul, is supported in Genesis 5. In Genesis 5 it refers to man, adam, being made in the image of God, and goes on to describe the generation of Adam, the first man.

1This is the book of the generations of Adam. In the day when God created man, He made him in the likeness of God. 2 He created them male and female, and He blessed them and named them Man in the day when they were created. 3 When Adam had lived one hundred and thirty years, he became the father of a son in his own likeness, according to his image, and named him Seth. 4 Then the days of Adam after he became the father of Seth were eight hundred years, and he had other sons and daughters. 5 So all the days that Adam lived were nine hundred and thirty years, and he died.
Genesis 5:1-5, NASB

It's also supported by Genesis 9, which refers to man of Noah's time as alike being created in His image.

1 And God blessed Noah and his sons and said to them, “Be fruitful and multiply, and fill the earth. 2 The fear of you and the terror of you will be on every beast of the earth and on every bird of the [a]sky; with everything that creeps on the ground, and all the fish of the sea, into your hand they are given. 3 Every moving thing that is alive shall be food for you; I give all to you, as I gave the green plant. 4 Only you shall not eat flesh with its life, that is, its blood. 5 Surely I will require your lifeblood; from every beast I will require it. And from every man, from every man’s brother I will require the life of man. 6 “Whoever sheds man’s blood, By man his blood shall be shed, For in the image of God He made man.
Genesis 9:1-6, NASB