Darwin studied actual birds on the galapagos islands instead of using a simulation, as you did in this lab. studying natural selection in the field can be challenging. list at least three possible challenges darwin might have faced.

In Darwin's time, natural selection was a strange theory among researchers and scientists. Before him various other scientists had postulated something regarding evolution, thus Darwin would have few people on his side, so it would have taken him some time to prove his theory.  

Another major issue Darwin would have faced would be the lack of technology, as in order to travel, Darwin had to use boats to go too far places, and thus, it would have taken ample of time.  

The final issue Darwin would have faced is that evolution is a natural phenomenon that takes millions of years to take place, as it does not happen overnight. Therefore, it would have taken him quite a long time to observe, conduct his experiments again and again, and then to finally come to a conclusion.  

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.

when it is at an intermediate population density