Question: how the earth's history can be interpreted from the geologic time scale

title: Geologic time scale
text: Ordovician Late Hirnantian Invertebrates diversify into many new types ( e.g. , long straight - shelled cephalopods ) . Early corals , articulate brachiopods ( Orthida , Strophomenida , etc . ) , bivalves , nautiloids , trilobites , ostracods , bryozoa , many types of echinoderms ( crinoids , cystoids , starfish , etc . ) , branched graptolites , and other taxa all common . Conodonts ( early planktonic vertebrates ) appear . First green plants and fungi on land . Ice age at end of period . 445.2 ± 1.4