Chapter 12: Fossils and Deep Time

fossils

remnants or traces of ancient living organisms, which were buried in sediment or other Earth materials and preserved after lithification

• most represent extinct species

• provide insights to nature of ancient life and ecosystems that hosted the organisms

fossils and time sequence

sequence of sedimentary strata: fossil species in lower beds differ from those in higher beds → time sequence

fossil successions

progressive changes in shape and size of individual species & in populations of organisms

deep time

document the evolution of organisms & environments over geological timescales

fossilization

transformation of the remains of organisms or of traces left behind by them, into a fossil

• fossils mostly found in sedimentary rocks

• preservation in sedimentary rocks

• burial through deposition of sediment → lithification

• e.g: preservation in permafrost

• fossils allow for reconstruction of organisms, including those that may be extinct (wooly mammoth)

different types of fossilization/preservation

• preservation in ice (Iceman)

• preservation in peat bogs (Weerdinge Men and Meenybraddan Woman)

• preservation in volcanic tuff (Pompeii, ITA)

  • burial through deposition of volcanic ash → lithification

• preservation in amber

  • amber = fossilized tree resin → resin is a fossil

  • many fossils, mostly insects enclosed in amber

types of fossils

• body fossils

• molds

• trace fossils (footprints, burrows, feeding traces)

• excrements

• eggs and nests

body fossils

• Belemnites = hard internal skeleton of squid-like animals

  

• fossil plankton shells (microfossils)

trace fossils

horizontal burrows developed on or just below seabed

• created by an unknown animal

• feeding traces of invertebrates on the bedding planes of fine-grained sedimentary rocks

excrements

fossilized feces (Corprolites)

eggs and nests

nest of dinosaur eggs