What is this children's book about Earth exploding?

I vaguely remember reading a book in the 5th grade about Earth being destroyed somehow and the inhabitants escape on ships and go in search of a new planet. On the new planet, the "grass" was like shards of glass and there were moth people that I think hatched from giant boulder-like eggs. I remember that before they found a new place to live, the people ate iron rations and no one liked them. Does anyone have any clue what this book might be?