Which of these best describes earth’s core?
a/ most dense layer, consists of the outer and inner parts.
b/ thinnest under the oceans and thickest under continents.
c/ middle layer, density increases with depth as pressure increases.
d/ least dense layer overall, consists of two layers of different thickness.

A

Explanation:

The answer is A. The core has two parts; the inner and outer core. Plus, scientist have concluded that the core is the most dense layer out of deductive reasoning and experiments. B would be the crust (or the top most layer of the earth). C is the mantle. D is also the core. :)

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation:

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.