Query: The geologic record provides us with abundant evidence for such perpetual natural climate variability, from icecaps reaching almost to the equator to none at all, even at the poles.

Relevant passages:
Triassic <=SEP=> The Triassic ( -LSB- prontraɪˈæsɪk -RSB- ) is a geologic period and system which spans 50.9 million years from the end of the Permian Period million years ago ( Mya ) , to the beginning of the Jurassic Period Mya . The Triassic is the first period of the Mesozoic Era . Both the start and end of the period are marked by major extinction events .   The Triassic began in the wake of the Permian -- Triassic extinction event , which left the earth 's biosphere impoverished ; it would take well into the middle of this period for life to recover its former diversity . Therapsids and archosaurs were the chief terrestrial vertebrates during this time . A specialized subgroup of archosaurs , called dinosaurs , first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period .   The first true mammals , themselves a specialized subgroup of Therapsids , also evolved during this period , as well as the first flying vertebrates , the pterosaurs , who like the dinosaurs were a specialized subgroup of archosaurs . The vast supercontinent of Pangaea existed until the mid-Triassic , after which it began to gradually rift into two separate landmasses , Laurasia to the north and Gondwana to the south .   The global climate during the Triassic was mostly hot and dry , with deserts spanning much of Pangaea 's interior . However , the climate shifted and became more humid as Pangaea began to drift apart . The end of the period was marked by yet another major mass extinction , the Triassic-Jurassic extinction event , that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic .   The Triassic was named in 1834 by Friedrich von Alberti , after the three distinct rock layers ( tri meaning `` three '' ) that are found throughout Germany and northwestern Europe -- red beds , capped by marine limestone , followed by a series of terrestrial mud - and sandstones -- called the `` Trias '' .

Mesozoic <=SEP=> The Mesozoic Era ( -LSB- pronˌmɛsəˈzoʊɪk , _ ˌmiː - , _ - soʊ - -RSB- or -LSB- ˌmɛzəˈzoʊɪk , _ ˌmiː - , _ - soʊ - -RSB- ) is an interval of geological time from about . It is also called the Age of Reptiles , a phrase introduced by the 19th century paleontologist Gideon Mantell who viewed it as dominated by diapsids such as Iguanodon , Megalosaurus , Plesiosaurus and Pterodactylus . This Era is also called from a paleobotanist view the Age of Conifers .   Mesozoic means `` middle life '' , deriving from the Greek prefix meso - / μεσο - for `` between '' and zōon / ζῷον meaning `` animal '' or `` living being '' . It is one of three geologic eras of the Phanerozoic Eon , preceded by the Paleozoic ( `` ancient life '' ) and succeeded by the Cenozoic ( `` new life '' ) . The era is subdivided into three major periods : the Triassic , Jurassic , and Cretaceous , which are further subdivided into a number of epochs and stages .   The era began in the wake of the Permian -- Triassic extinction event , the largest well-documented mass extinction in Earth 's history , and ended with the Cretaceous -- Paleogene extinction event , another mass extinction which is known for having killed off non-avian dinosaurs , as well as other plant and animal species . The Mesozoic was a time of significant tectonic , climate and evolutionary activity . The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would eventually move into their current positions . The climate of the Mesozoic was varied , alternating between warming and cooling periods . Overall , however , the Earth was hotter than it is today . Dinosaurs appeared in the Late Triassic and became the dominant terrestrial vertebrates early in the Jurassic , occupying this position for about 135 million years until their demise at the end of the Cretaceous . Birds first appeared in the Jurassic , having evolved from a branch of theropod dinosaurs . The first mammals also appeared during the Mesozoic , but would remain small -- less than 15 kg ( 33 lb ) -- until the Cenozoic .

Paleocene <=SEP=> The Paleocene ( -LSB- pronˈpæliəˌsiːn , _ ˈpæ - , _ - lioʊ - -RSB- ) or Palaeocene , the `` old recent '' , is a geologic epoch that lasted from about . It is the first epoch of the Paleogene Period in the modern Cenozoic Era . As with many geologic periods , the strata that define the epoch 's beginning and end are well identified , but the exact ages remain uncertain .   The Paleocene Epoch brackets two major events in Earth 's history . It started with the mass extinction event at the end of the Cretaceous , known as the Cretaceous -- Paleogene ( K -- Pg ) boundary . This was a time marked by the demise of non-avian dinosaurs , giant marine reptiles and much other fauna and flora . The die-off of the dinosaurs left unfilled ecological niches worldwide . The Paleocene ended with the Paleocene -- Eocene Thermal Maximum , a geologically brief ( ~ 0.2 million year ) interval characterized by extreme changes in climate and carbon cycling .   The name `` Paleocene '' comes from Ancient Greek and refers to the `` old ( er ) '' ( παλαιός , palaios ) `` new '' ( καινός , kainos ) fauna that arose during the epoch .