Why are earths materials and energy considered to be in equilibrium
-earths materials are recycled and reused constantly
-earths materials are all divided in equal amounts
-energy is balanced and cannot be created or destroyed
-energy is always converted into usable forms

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands