All of these are caused by water in some way, however, gully erosion is due to steady and fast-flowing streams; the Grand Canyon is an excellent example of the effect of gully erosion. Splash erosion is the first step in erosion from water, and involves the breakage of soil via the impact between soil and a raindrop. It is often a precursor for other types of erosion since it loosens soil. Sheet erosion involves evenly removing a certain number of layers of material due to regular water patterns. Rill erosion is a result of small, well-defined paths of water known as rills, that flow downhill after rainfall. 

The correct response is Milankovitch cycles. This theory describes how the orbit, tilt, and axis of the Earth operate on a 100,000 year cycle that cause the Earth to be further from the sun. As the Earth gets farther from the sun, it can trigger an ice age. The theory is aptly named after the man who discovered it. The El Nino and La Nina events occur on a much shorter time scale and have nothing to do with ice ages. 

Today, 99.9% of all species that have ever existed on Earth are extinct. We are currently in the middle of the 6th mass extinction. The dinosaurs went extinct during the 5th, the Cretaceous, about 65 million years ago.

The Wallace Line, named for Alfred Russel Wallace, is a boundary that separates Asia and Australia. Wallace noticed that the some of the islands in this region contained species common to Australia and some contained species common to Asia, none of which would have crossed the open water in between the continents. Wallace correctly reasoned that this meant that sea levels were once much lower, an artifact of the last glacial maximum.

Sharks and dolphins are not closely related and evolved their streamlined shapes separately from one another. This is an example of convergent evolution, in which two species that are not closely related evolve similar characteristics. Divergent evolution is the opposite.

Prokaryotes are simple, single-celled organisms which lack membrane bound nuclei. They developed before any of the other listed answer choices, as all of the other listed answer choices are multi-celled organisms that developed from prokaryotes.

Evolution is a process of orderly and gradual change or development. The theory that all living species have developed as a result of changes in their genetic material over time. Evolution is a change in the proportions of different genotypes in a population from one generation to the next. The characteristic of an organism that helps it survive and reproduce in a particular environment is adaptation. Variability is the range of alterations present in a genome, such as the number of diverse alleles of a specific gene. The differences in reproductive output among individuals of a population, normally as a result of genetic differences is differential reporduction. Gene flow is the movement of alleles from one population to another owing to the migration of individual organisms. 

Coevolution occurs when one species evolves at the same time as another related species. Often one of these species is a prey-animal that adapts or develops traits that increase survival and reproductive rates. The predator that hunts the prey is required to adapt, increasing favorable traits that allow them, once again, to be able to hunt the prey. Coevolution is a type of evolution, but is not a cause of evolution.

Speciation is a general term referring to evolutionary processes leading to the creation of a new species. This occurs when a parent species is divided into at least two groups that are isolated from each other. These isolated groups adapt and mutate separately until they are no longer compatible for breeding.

Evolution caused by geographic isolation takes place when a species is separated into multiple groups due to a physical barrier of some kind (like a rock fall blocking a previously open canyon).

Evolution due to reproductive isolation occurs when members of two species that were previously able to produce viable offspring cannot due to changes in physical characteristics or behaviors. These species can procreate, but their offspring are not viable (able to reproduce).

The correct answer is coevolution. It is defined as the continual evolution that interacting species have in response to each other.

The correct response is: genetic drift is completely random. It is a natural process that occurs at random and has profound impacts on species. Thus, genetic drift was not created by humans - it's a natural process. Genetic drift occurs in life forms, from the prokaryotes to the eukaryotes. And genetic drift occurs in all living organisms: plants, animals, bacteria, and fungi.