What is an downward arching rock layer

So  if  the sum of the enthalpies of the reactants is greater than the products, the  reaction  will be  exothermic.  if  the products side has a larger enthalpy, the  reaction  is  endothermic. you may wonder why  endothermic reactions, which soak up energy or enthalpy from the environment, even happen

Its led to migrationits led to death 

Ithink the best answer is d increased stability of all other biomes

Can you maybe send me a screen shot of the map? it would really me you. : )