Paleocene

The Paleocene (<a href="/facts/International_Phonetic_Alphabet/2e7jmUaG">IPA</a>: /ˈpæli.əsiːn, -i.oʊ-, ˈpeɪli-/ PAL-ee-ə-seen, -⁠ee-oh-, PAY-lee-), or Palaeocene, is a geological <a href="/facts/Epoch_(geology)/RhfBWrP2">epoch</a> that lasted from about 66 to 56 <a href="/facts/Mya_(unit)/DXcnXuAw">million years ago</a> (mya). It is the first epoch of the <a href="/facts/Paleogene/CNsEpdA4">Paleogene</a> <a href="/facts/Period_(geology)/6LBR11yQ">Period</a> in the modern <a href="/facts/Cenozoic/yFslcz6n">Cenozoic</a> <a href="/facts/Era_(geology)/0gqadCDc">Era</a>. The name is a combination of the <a href="/facts/Ancient_Greek/LIK7NlUh">Ancient Greek</a> παλαιός palaiós meaning "old" and the <a href="/facts/Eocene/EYgI8Uco">Eocene</a> Epoch (which succeeds the Paleocene), translating to "the old part of the Eocene".
The epoch is bracketed by two major events in Earth's history. The <a href="/facts/K%E2%80%93Pg_extinction_event/HNyDuEcx">K–Pg extinction event</a>, brought on by an asteroid impact (<a href="/facts/Chicxulub_impact/qVqCqm81">Chicxulub impact</a>) and possibly volcanism (<a href="/facts/Deccan_Traps/HdvPLMuQ">Deccan Traps</a>), marked the beginning of the Paleocene and killed off 75% of species, most famously the non-avian dinosaurs. The end of the epoch was marked by the <a href="/facts/Paleocene%E2%80%93Eocene_Thermal_Maximum/QnPVzRR7">Paleocene–Eocene Thermal Maximum</a> (PETM), which was a major climatic event wherein about 2,500–4,500 gigatons of carbon were released into the atmosphere and ocean systems, causing a spike in global temperatures and <a href="/facts/Ocean_acidification/GE7MrSPj">ocean acidification</a>.
In the Paleocene, the continents of the <a href="/facts/Northern_Hemisphere/EFwyqL25">Northern Hemisphere</a> were still connected via some <a href="/facts/Land_bridge/WT3Jzmgu">land bridges</a>; and South America, Antarctica, and Australia had not completely separated yet. The <a href="/facts/Rocky_Mountains/rDc3cU0E">Rocky Mountains</a> were being uplifted, the Americas had not yet joined, the <a href="/facts/Indian_Plate/Apeb9LNF">Indian Plate</a> had begun its collision with Asia, and the <a href="/facts/North_Atlantic_Igneous_Province/oNWVlDD4">North Atlantic Igneous Province</a> was forming in the third-largest <a href="/facts/Magma/hRotHju9">magmatic</a> event of the last 150 million years. In the oceans, the <a href="/facts/Thermohaline_circulation/GNXdegku">thermohaline circulation</a> probably was much different from what it is today, with downwellings occurring in the North Pacific rather than the North Atlantic, and water density mainly being controlled by <a href="/facts/Salinity/X6mB1YAM">salinity</a> rather than temperature.
The K–Pg extinction event caused a floral and faunal turnover of species, with previously abundant species being replaced by previously uncommon ones. In the Paleocene, with a global average temperature of about 24–25 °C (75–77 °F), compared to 14 °C (57 °F) in more recent times, the Earth had a <a href="/facts/Greenhouse_and_icehouse_Earth/ENS3leWV">greenhouse climate</a> without permanent ice sheets at the poles, like the preceding <a href="/facts/Mesozoic/yYsvXGPa">Mesozoic</a>. As such, there were forests worldwide—including at the poles—but they had low <a href="/facts/Species_richness/xb1W1j65">species richness</a> in regards to plant life, and were populated by mainly small creatures that were rapidly evolving to take advantage of the recently emptied Earth. Though some animals attained great size, most remained rather small. The forests grew quite dense in the general absence of large herbivores. <a href="/facts/Mammal/phSwTzBo">Mammals</a> proliferated in the Paleocene, and the earliest <a href="/facts/Placental/xegVWIRG">placental</a> and <a href="/facts/Marsupial/zN5s4bMq">marsupial</a> mammals are recorded from this time, but most Paleocene <a href="/facts/Taxa/caQC1e87">taxa</a> have ambiguous <a href="/facts/Affinity_(taxonomy)/t6snCwdz">affinities</a>. In the seas, <a href="/facts/Ray-finned_fish/3PNaXXmJ">ray-finned fish</a> rose to dominate open ocean and recovering reef ecosystems.

Paleocene open-in-new

Paleocene