The fossil remains of animals with body plans recognizable as arthropods, echinoderms, mollusks, and other bilaterians first appeared during the Period, around million years ago.

              The fossils remains of arthropods, Echinoderms, Mollusk and other bilaterians appeared in Cambrian period and throughout the Paleozoic era.

Explanation:

                      Trilobites were marine group of arthropods that appeared in the Cambrian Period around 55.6 million years ago, eventually becoming extinct during the Permian Period. Most of the organisms were  small, bottom-dwelling organisms that had fed on small organic matters in sediment on the sea bottom. The body is divided in three segments: head (cephalon), middle (thorax), and tail (pygidium). Many species had large, compound eyes. Fossils had define characters of having body divided in to head,thorax,and tail. Body had segmentation and citineious body layer.

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.