It is difficult to imagine how only part of an adaptation could function, but darwin explained this. how would he answer the question, “what good is 5% of an eye? ”

a) once an organism has the first 5% of an adaptation, the rest will quickly evolve.
b) five percent of an eye is always better than a full eye since it is easier to grow. the difficulty is in explaining fully formed eyes.
c) since variation is random, we don’t expect to see more than about 5% of an eye in any species.
d) five percent of an eye, perhaps a simple light-sensitive spot, is often better than having no eye at all.

5 % of an eye suggests that simple light sensitive spot on skin is better than having no eye or light sensitivity at all.

Option D

During the explanation of human eye formation, Darwin with his new theory faced several difficulties. As the human eye has several dependent parts like lens, pupil, retina, choroid etc and absence of any of these could impair vision, thus the natural selection or evolution of all of them as a whole is not explained by Darwin.

But Darwin explained the eye formation of humans as first the presence of light sensitive area on skin of some primitive animals which gave them advantages over the ones who lack them, and natural selection favored those species which had this spot.

Now some random changes led to the deepening of this spot which gave them sharper vision, then the aperture of this deepening decreased until a small hole, like a pinhole camera. Then the lens developed like a transparent fold of skin with fluid inside, which led to the formation of lens for accommodation. This is the 5% development rate which Darwin suggested.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.

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