What is the Gaia Hypothesis?

The instructions for the genetic traits of an organism are directly determined by the a-numbers of a,t,c and g units in a sugar molecule b-sequence of the bases in dna molecules c-length of a dna molecules d-way the bases are paired in the two strands of a dna molecule

My question says on my assignment. read the following scenarios and decide which of the properties of life are being described. the first one is. katherine stopped on the way to school to grab some donuts. 2. because a dog cannot sweat, it has to pant in order to stay cool. 3. an elephant trun had no bone but 4,000 muscles. i have no idea what i am supposed to anwer. i can't find the answer in my notes or book that i can understand anyway

What is thought to have caused the mass extinction at the end of the cretaceous period?