How do mantle-derived magmas that have a basaltic composition generate magmas that exhibit an intermediate to felsic composition? How do mantle-derived magmas that have a basaltic composition generate magmas that exhibit an intermediate to felsic composition? As basaltic magma ascends through the thick continental crust, ferromagnesian minerals crystallize and drop out of the melt, thus creating a secondary melt of an intermediate or a felsic composition. As basaltic magma ascends through the thick continental crust, non-ferromagnesian minerals crystallize and drop out of the melt, thus creating a secondary melt of an intermediate or a felsic composition. As basaltic magma ascends through the thick continental crust, ferromagnesian minerals crystallize and drop out of the melt, thus creating a primary melt of an intermediate or a felsic composition. Partial melting of peridotite directly generates magma of an intermediate or a felsic composition. As basaltic magma ascends through the thick continental crust, non-ferromagnesian minerals crystallize and drop out of the melt, thus creating a secondary melt of an intermediate or a felsic composition.

Scientist: cross-sections of stalactites—calcite formations deposited on cave ceilings by seeping water—can reveal annual variations in rainfall in particular areas over hundreds and thousands of years. we often found that when—according to these cross-sections—drought occurred in a particular area, it coincided with the collapse of an ancient society in that area. i hypothesize that drought reduced agricultural productivity in these areas, thereby leaving these societies without the resources needed to handle internal stresses and external threats. which of the following, if true, would most weaken the support for the scientist's hypothesis? a. many droughts indicated in the cross-sections of stalactites do not correspond with the collapse of a society in that area. b. information from the cross-sections of stalactites alone cannot reveal the level of agricultural output in an area at a particular time. c. most of the societies that collapsed during droughts did so when internal power struggles coincided with military raids from neighboring societies. d. most of the societies that collapsed during droughts maintained large stockpiles of food and water at the time of their collapse. e. information from stalactites also suggests that the collapse of some societies coincided with periods of abnormally high rainfall.