Paleontology and geology
The Precambrian: Most of the Precambrian rocks in New Jersey are igneous or metamorphic and do not contain any fossils. However, stromatolites have been found in some 1.2 billion-year-old marbles, indicating that marine conditions existed locally in the state at that time.
The Paleozoic: Paleozoic rocks are well represented in northern New Jersey. Cambrian-age trilobites and stromatolites record the presence of a warm, shallow sea, while deeper water conditions prevailed during the Ordovician. Uplift and erosion in the Early Silurian provided sediment that contributed to thick sequences of river deposits in the northern part of the state. Marine fossils in rocks inter-layered with the river sediments indicate intermittent incursions of the sea. Warm, shallow seas returned to northwestern New Jersey from the Late Silurian into the Devonian. Brachiopods, bryozoans, corals, and crinoids are among the common fossils found. Any Carboniferous and Permian rocks that might have been present in New Jersey have been eroded away.
The Mesozoic: The Mesozoic rocks of New Jersey record the beginnings of the break-up of the supercontinent of Pangea and the creation of the Newark Rift Basin. Blocks of crust dropped downward along faults and then filled with lakes and sediment eroding off the surrounding highlands. Fossils of early reptiles are found in the Triassic sedimentary rocks. Rifting continued into the Jurassic, and the basin continued to fill with sediments and lava flows. Footprints preserved in the sedimentary rocks indicate that bipedal dinosaurs roamed New Jersey during this time. Most of northern New Jersey was above sea level during the Cretaceous, while in southern New Jersey, seas moved in and out over the coastal plain providing a variety of habitats from terrestrial to continental shelf. Insect and leaf fossils indicate that low-lying areas were covered by vegetation, while tracks and bones show dinosaurs inhabited the landscape. Mosasaurs, sharks, and squid-like animals swam the seas, while clams and oysters thrived on the sea floor below.
The Cenozoic: Marine life continued to flourish in the Tertiary seas of southern New Jersey and fossils of brachiopods, shark teeth, corals, echinoderms, and microscopic organisms indicate that the waters were warmer than those off the coast today. Ice sheets advanced and retreated over northern New Jersey during the Quaternary, and sea level fluctuated as the glaciers alternately grew and melted. Mastodons, mammoths, and other mammals roamed the land in front of the ice sheets.