Why are the sister chromatids in the daughter in meiosis different than the sister chromatids in the parent cell?

In meiosis, the outcome goal is to produce a haploid gamete - a sex cell with only one chromosome for each pair (instead of a full diploid pair) with the potential to join with another gamete - to form a new organism. 

During Meiosis I, crossing over occurs; chromosomes exchange parts, increasing diversity of offspring. Every crossing over event is random and no two resulting chromatids are the same. Therefore, no daughter cell's chromatids will be exactly the same.

Gases enter the atmosphere and trap the sun's heat warning the earth.