Why are there two different creation stories in Genesis?

I have been conducting a discussion with a non-believer who has requested that I post the following examples of what he feels constitute Biblical “contradictions.” I referred him to the excellent apologetics service at this site and I hope someone might perhaps provide a response I can refer him to. Thank you very much for your help:
“Ask them to explain these seemingly contradictory stories.The first is given in Genesis 1: 1-2:4 while the second is given in Genesis 2: 4-24.”

Catechism of the Catholic Church:

289 Among all the Scriptural texts about creation, the first three chapters of Genesis occupy a unique place. From a literary standpoint these texts may have had diverse sources. The inspired authors have placed them at the beginning of Scripture to express in their solemn language the truths of creation - its origin and its end in God, its order and goodness, the vocation of man, and finally the drama of sin and the hope of salvation. Read in the light of Christ, within the unity of Sacred Scripture and in the living Tradition of the Church, these texts remain the principal source for catechesis on the mysteries of the “beginning”: creation, fall, and promise of salvation.

Humani Generis

“…the first eleven chapters of Genesis, although properly speaking not conforming to the historical method used by the best Greek and Latin writers or by competent authors of our time, do nevertheless pertain to history in a true sense, which however must be further studied and determined by exegetes; the same chapters, (the Letter points out), in simple and metaphorical language adapted to the mentality of a people but little cultured, both state the principal truths which are fundamental for our salvation, and also give a popular description of the origin of the human race and the chosen people. If, however, the ancient sacred writers have taken anything from popular narrations (and this may be conceded), it must never be forgotten that they did so with the help of divine inspiration, through which they were rendered immune from any error in selecting and evaluating those documents."

For complete text click here.

Concerning the apparent contradictions of the two creation accounts in Genesis 1-2, I recommend the following:

**Papal writings:
**From the writings of Pope John Paul II:

“Catechesis on Genesis” - Analysis of the Biblical Account of Creation
Click here.

“Second Account of Creation” - The Subjective Definition of Man
Click here.

Recommended articles:[LIST]
*]Hexaemeron - the first six days of Creation
*]Adam, Eve, and Evolution[/LIST]"Commentary on Genesis"
By Father William Most
Click here.

** Recommended books:
Free From All Error
By Fr. William G. Most
Electronic copy:

Handbook of Christian Apologetics
By Peter Kreeft and Ronald K. Tacelli

"Genesis is a Book"
By Jeremy Holmes
Click here.

"A Neo-Patristic Return to the First Four Days of Creation"
Click here.

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