GENERAL HISTOLOGY

Detailed explanation-1: -During the Cambrian, land plants had not yet evolved, so the terrestrial world was devoid of vegetation. However, in the oceans many marine invertebrates, including sponges and brachiopods (lamp shells), were present.

Detailed explanation-2: -As noted above, trilobites are the most common fossil types, and these dominant animals of the Cambrian seas characterize this Period. Each division of the Cambrian is identified with particular trilobite genera.

Detailed explanation-3: -During latest Precambrian time, the sea level was relatively low, resulting in spatially restricted oceans and expanded continents. Throughout much of the Cambrian, rising seas gradually flooded vast land areas. Sediment was eroded from the continents and deposited in adjacent seas.

Detailed explanation-4: -The Cambrian period, part of the Paleozoic era, produced the most intense burst of evolution ever known. The Cambrian Explosion saw an incredible diversity of life emerge, including many major animal groups alive today. Among them were the chordates, to which vertebrates (animals with backbones) such as humans belong.