As the colorado plateau continues to rise, the colorado river cuts deeper and deeper into it; therefore, much of the grand canyon is
a. a primary landform
b. a secondary landform
c. a tertiary landform
d. not a landform, since canyons cannot be landforms

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

Of seawater increases with decrease in the temperature. therefore, the cold water sinks to the deeper layers at the bottom

What best explains the inability for life to exist in earth early atmosphere