Why are index fossils helpful? A. Since they are only from a specific time period, the rock layer they are found in, and all
fossils within it, must also be from that time period. This helps scientists date fossils.

b. They are the only radioactive fossils and so help scientists find its specific age

c. They never break down, like other fossils, so they are a permanent glimpse into
history.

Subduction zones form when an oceanic plate collides with another oceanic plate or continental plate. the continental crust is lighter and less dense than oceanic crust. continental crust's density is approximately 2.7 grams per cubic centimeter. oceanic crust is thinner and the average density is about 3.3 cubic centimeters. when the two crustal plates converge the oceanic plate always bends and subducts beneath a continental plate. once the oceanic crust subjects, the rocks are subjected to changes in heat and pressure. because of this, we would expect to find rocks in the area of a subduction. a) clastic b) igneous c) metamorphic d) sedimentary