they all know that, well except for ax. but all cassie and jake were thinking about was saving the mecoras. and all rachel and marco were thinking about was getting back home in one piece.
The Mecoras are the ones who introduced broccoli to Earth. But since their settlement was ground zero, how did any of the broccoli survive?
Seeds tend to survive 
It was a really big meteor. I figure that all of the brocolli fields would have been within the crater made by the meteor, and that the heat of impact would have vaporized all the seeds.
Also, any surviving seeds would have to cope with the subsequent nuclear winter.
