What circumstances does crossing over result in new combination's of genes in gametes?

Imagine a rocket launching from earth and travelling to the moon. in which order would the rocket pass through the layers of the atmosphere? thermosphere, mesosphere, stratosphere, troposphere troposphere, mesosphere, stratosphere, troposphere thermosphere, stratosphere, mesosphere, troposphere troposphere, stratosphere, mesosphere, thermosphere

Which mechanism of transport takes place when solute particles move from a region of high concentration to a region of low concentration? active diffusion isotonic osmosis

Several billion years ago which gas was the least prevailant in the atmosphere