How does sonar technology measure the depth of the ocean floor? A
The device sends sound signals to the ocean floor and records the time it takes for each signal to return.

B
The device receives electromagnetic energy that is emitted by cooling oceanic crust.

C
The device lowers a cord from a ship to the bottom of the ocean and records the cord's length.

the circled areas are referred to   as sunspots.   the sunspots are cooler than the   surrounding area.

sunspots are temporary phenomena on the photosphere of the sun that appear visibly as dark spots compared to surrounding regions. they correspond to concentrations of magnetic field flux that inhibit convection and result in reduced surface temperature compared to the surrounding photosphere.

all these collisions do one thing, and that thing is explained in the last option. when dusst, rocks and ice collide, they harden and form giant layers of rocks or hard ice.

d)   to harden materials to form different parts of earth’s layers

hope it ,

bioteacher101