Tertiary Period | Events, Climate, & Organisms

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border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/science/Tertiary-Period">Tertiary Period</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/Tertiary-Period">Introduction</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref69991"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/Tertiary-Period#ref69991">Tertiary environment</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref69992"><a class="w-100 link-gray-900" href="/science/Tertiary-Period#ref69992">Paleogeography</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref69994"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Paleoclimate">Paleoclimate</a></li></ul></div></li><li data-target="#ref69995"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Paleoclimate#ref69995">Tertiary life</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref275674"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Paleoclimate#ref275674">Life on land</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref275675"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Paleoclimate#ref275675">Flowering plants and grasses</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref275676"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Paleoclimate#ref275676">Birds</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref275677" class="has-children"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/The-rise-of-mammals">The rise of mammals</a><ul class="list-unstyled" data-level="h4"><li data-target="#ref275678"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/The-rise-of-mammals#ref275678">Mammalian migration from Eurasia to North America</a></li></ul><ul class="list-unstyled" data-level="h4"><li data-target="#ref275679"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/The-rise-of-mammals#ref275679">Mammalian migration between North and South America</a></li></ul><ul class="list-unstyled" data-level="h4"><li data-target="#ref275680"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Primates">Primates</a></li></ul></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref275681"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Life-in-the-oceans">Life in the oceans</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref275682"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Life-in-the-oceans#ref275682">Marine extinctions and recovery</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref275683"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Life-in-the-oceans#ref275683">Radiation of invertebrates</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref275684"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Life-in-the-oceans#ref275684">Large marine animals</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref275685"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Life-in-the-oceans#ref275685">Foraminiferans</a></li></ul></li></ul></div></li><li data-target="#ref69984"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Tertiary-rocks">Tertiary rocks</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref275686"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Tertiary-rocks#ref275686">Major subdivisions of the Tertiary System</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref275687"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Tertiary-rocks#ref275687">Occurrence and distribution of Tertiary deposits</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref275688"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Volcanism-and-orogenesis">Volcanism and orogenesis</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref275689"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Volcanism-and-orogenesis#ref275689">Sedimentary sequences</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref275690"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Establishing-Tertiary-boundaries">Establishing Tertiary boundaries</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref69989"><a class="w-100 link-gray-900" href="/science/Tertiary-Period/Correlation-of-Tertiary-strata">Correlation of Tertiary strata</a></li></ul></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/Tertiary-Period/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/Tertiary-Period">Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" href="https://www.britannica.com/science/Tertiary-Period/images-videos">Images & Videos</a> <div class="slider js-slider position-relative d-inline-flex align-items-center mw-100 "> <div class="slider-container js-slider-container overflow-hidden d-flex overflow-hidden text-nowrap ml-15"> <a href="https://cdn.britannica.com/22/148022-050-CA2C991E/Gypsum-cones-evaporation-basin-Mediterranean-Sea-Sorbas.jpg" data-href="/media/1/588461/153655" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/22/148022-004-46F75543/Gypsum-cones-evaporation-basin-Mediterranean-Sea-Sorbas.jpg" alt="Messinian Stage" height="50" /> </a> <a href="https://cdn.britannica.com/43/136143-050-8C4B3AF6/Distribution-landmasses-regions-seas-middle-ocean-basins.jpg" data-href="/media/1/588461/146756" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/43/136143-004-0FC92E84/Distribution-landmasses-regions-seas-middle-ocean-basins.jpg" alt="Eocene paleogeography" height="50" /> </a> <a href="https://cdn.britannica.com/67/73167-050-C66534D1/chart.jpg" data-href="/media/1/588461/66800" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/67/73167-004-106002DC/chart.jpg" alt="geologic time" height="50" /> </a> <a href="https://cdn.britannica.com/11/811-004-A82F76A6/Distribution-landmasses-regions-seas-ocean-basins-currents.jpg" data-href="/media/1/588461/1702" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/11/811-004-A82F76A6/Distribution-landmasses-regions-seas-ocean-basins-currents.jpg" alt="Tertiary paleogeography" height="50" /> </a> <a href="https://cdn.britannica.com/13/813-004-10B408EB/Cenozoic-migration-routes-barriers.jpg" data-href="/media/1/588461/1701" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/13/813-004-10B408EB/Cenozoic-migration-routes-barriers.jpg" alt="Cenozoic migration routes" height="50" /> </a> <a href="https://cdn.britannica.com/10/6010-050-56184E94/Mediterranean-Sea.jpg" data-href="/media/1/588461/614" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/10/6010-004-373EBA60/Mediterranean-Sea.jpg" alt="Mediterranean Sea" height="50" /> </a> <a href="https://cdn.britannica.com/64/95064-050-0EA553A5/Perito-Moreno-Glacier-Argentina-Los-Glaciares-National.jpg" data-href="/media/1/588461/92512" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/64/95064-120-AA0FBC7D/Perito-Moreno-Glacier-Argentina-Los-Glaciares-National.jpg" alt="Perito Moreno Glacier" height="50" /> </a> <a href="https://cdn.britannica.com/08/76808-050-0B37F4BC/impact-Earth-region-conception-artist-Caribbean-collision.jpg" data-href="/media/1/588461/88835" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/08/76808-004-A4853265/impact-Earth-region-conception-artist-Caribbean-collision.jpg" alt="near-Earth object: impact" height="50" /> </a> <a href="https://cdn.britannica.com/39/12339-004-C8BCEF15/reconstruction-Diatryma-skeleton.jpg" data-href="/media/1/588461/5208" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/39/12339-004-C8BCEF15/reconstruction-Diatryma-skeleton.jpg" alt="Diatryma" height="50" /> </a> <a href="https://cdn.britannica.com/71/3471-004-B85B6C73/Phenacodus-Charles-R-Knight-1898.jpg" data-href="/media/1/588461/6907" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/71/3471-004-B85B6C73/Phenacodus-Charles-R-Knight-1898.jpg" alt="Phenacodus" height="50" /> </a> </div> <button disabled class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue " aria-label="Previous"> <span class="material-icons md-24" 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They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <a class="byline-edit-history" href="https://www.britannica.com/science/Tertiary-Period/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn btn-sm border-2 btn-outline-red-400 border-red-400 module-spacing js-inline-ai-ask-button p-10 ml-5"> Ask the Chatbot </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Key People: </dt> <dd><a href="/biography/Alexandre-Brongniart" topicid="80939">Alexandre Brongniart</a></dd> <dd><a href="/biography/Edward-Drinker-Cope" topicid="136500">Edward Drinker Cope</a></dd> <dd><a href="/biography/Jean-Baptiste-Julien-d-Omalius-dHalloy" topicid="428209">Jean-Baptiste-Julien d’ Omalius d’Halloy</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/science/fossil" topicid="214511">fossil</a></dd> <dd><a href="/science/K-T-extinction" topicid="1314796">K–T extinction</a></dd> <dd><a href="/science/Paleocene-Eocene-Thermal-Maximum" topicid="1419455">Paleocene-Eocene Thermal Maximum</a></dd> <dd><a href="/science/Paleogene-Period" topicid="439462">Paleogene Period</a></dd> <dd><a href="/science/Neogene-Period" topicid="408872">Neogene Period</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/Tertiary-Period"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><div class="assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100" data-type="other"><div class="slider-container js-slider-container overflow-hidden d-flex"><div class="rw-track d-flex align-items-center"><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="146756" data-asm-type="image"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/43/136143-050-8C4B3AF6/Distribution-landmasses-regions-seas-middle-ocean-basins.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/588461/146756"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/43/136143-050-8C4B3AF6/Distribution-landmasses-regions-seas-middle-ocean-basins.jpg"><img src="https://cdn.britannica.com/43/136143-050-8C4B3AF6/Distribution-landmasses-regions-seas-middle-ocean-basins.jpg?w=300" alt="Eocene paleogeography" data-width="1600" data-height="979" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/43/136143-050-8C4B3AF6/Distribution-landmasses-regions-seas-middle-ocean-basins.jpg" data-href="/media/1/588461/146756">Eocene paleogeography</a><span>Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the middle of the Eocene Epoch of the Paleogene Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div></div><button disabled="true" class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_left"></span></button><button disabled="true" class="next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_right"></span></button></div><p class="topic-paragraph"><strong><span id="ref586081"></span>Tertiary Period</strong>, former official interval of <a href="https://www.britannica.com/science/geologic-time" class="md-crosslink " data-show-preview="true">geologic time</a> lasting from approximately 66 million to 2.6 million years ago. It is the traditional name for the first of two periods in the <a href="https://www.britannica.com/science/Cenozoic-Era" class="md-crosslink " data-show-preview="true">Cenozoic Era</a> (66 million years ago to the present); the second is the <a href="https://www.britannica.com/science/Quaternary" class="md-crosslink " data-show-preview="true">Quaternary Period</a> (2.6 million years ago to the present). The Tertiary has five principal subdivisions, called epochs, which from oldest to youngest are the <a href="https://www.britannica.com/science/Paleocene-Epoch" class="md-crosslink " data-show-preview="true">Paleocene</a> (66 million to 55.8 million years ago), <a href="https://www.britannica.com/science/Eocene-Epoch" class="md-crosslink " data-show-preview="true">Eocene</a> (55.8 million to 33.9 million years ago), <a href="https://www.britannica.com/science/Oligocene-Epoch" class="md-crosslink " data-show-preview="true">Oligocene</a> (33.9 million to 23 million years ago), <a href="https://www.britannica.com/science/Miocene-Epoch" class="md-crosslink " data-show-preview="true">Miocene</a> (23 million to 5.3 million years ago), and <a href="https://www.britannica.com/science/Pliocene-Epoch" class="md-crosslink " data-show-preview="true">Pliocene</a> (5.3 million to 2.6 million years ago).</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">Beginning in the late 20th century, a number of authorities preferred not to use the terms Tertiary and Quaternary, preferring instead to divide the time intervals <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="encompassed" href="https://www.merriam-webster.com/dictionary/encompassed" data-type="MW">encompassed</a> by each into two different intervals known as the <a href="https://www.britannica.com/science/Paleogene-Period" class="md-crosslink " data-show-preview="true">Paleogene Period</a> (66 million to 23 million years ago) and the <a href="https://www.britannica.com/science/Neogene-Period" class="md-crosslink " data-show-preview="true">Neogene Period</a> (which previously spanned the interval between 23 million years ago and the present). In 2005 the International Commission on Stratigraphy (ICS) decided to recommend keeping the Tertiary and Quaternary in their geologic time scale but only as sub-eras within the Cenozoic. The sub-era structure was abandoned by the ICS in 2008, and the Tertiary Period became officially replaced by the Paleogene and Neogene periods. (At present, the Neogene <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="encompasses" href="https://www.merriam-webster.com/dictionary/encompasses" data-type="MW">encompasses</a> the interval between 23 million and 2.6 million years ago.)</p><span class="marker MOD2 mod-inline"></span><span class="marker PREMOD3 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="66800" data-asm-type="image"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/67/73167-050-C66534D1/chart.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/588461/66800"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/67/73167-050-C66534D1/chart.jpg"><img src="https://cdn.britannica.com/67/73167-050-C66534D1/chart.jpg?w=300" alt="geologic time" data-width="2000" data-height="1500" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/67/73167-050-C66534D1/chart.jpg" data-href="/media/1/588461/66800">geologic time</a><span>The stratigraphic chart of geologic time.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">The Tertiary was an interval of enormous geologic, climatic, oceanographic, and biological change. It spanned the transition from a globally warm world containing relatively high sea levels and dominated by reptiles to a world of polar <a href="https://www.britannica.com/science/glacier" class="md-crosslink " data-show-preview="true">glaciation</a>, sharply <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="differentiated" href="https://www.merriam-webster.com/dictionary/differentiated" data-type="MW">differentiated</a> <a href="https://www.britannica.com/topic/classification-1703397" class="md-crosslink " data-show-preview="true">climate zones</a>, and mammalian dominance. It began in the aftermath of the mass <a href="https://www.britannica.com/science/extinction-biology" class="md-crosslink " data-show-preview="true">extinction</a> event that occurred at the very end of the <a href="https://www.britannica.com/science/Cretaceous-Period" class="md-crosslink " data-show-preview="true">Cretaceous Period</a> (the so-called K-T boundary), when as much as 80 percent of <a href="https://www.britannica.com/science/species-taxon" class="md-crosslink " data-show-preview="true">species</a>, including the <a href="https://www.britannica.com/animal/dinosaur" class="md-crosslink " data-show-preview="true">dinosaurs</a>, disappeared. The Tertiary witnessed the dramatic evolutionary expansion of not only <a href="https://www.britannica.com/animal/mammal" class="md-crosslink " data-show-preview="true">mammals</a> but also <a href="https://www.britannica.com/plant/angiosperm" class="md-crosslink " data-show-preview="true">flowering plants</a>, <a href="https://www.britannica.com/animal/insect" class="md-crosslink " data-show-preview="true">insects</a>, <a href="https://www.britannica.com/animal/bird-animal" class="md-crosslink " data-show-preview="true">birds</a>, <a href="https://www.britannica.com/animal/coral" class="md-crosslink " data-show-preview="true">corals</a>, deep-sea organisms, marine <a href="https://www.britannica.com/science/plankton" class="md-crosslink " data-show-preview="true">plankton</a>, and <a href="https://www.britannica.com/animal/mollusk" class="md-crosslink " data-show-preview="true">mollusks</a> (especially <a href="https://www.britannica.com/animal/clam" class="md-crosslink " data-show-preview="true">clams</a> and <a href="https://www.britannica.com/animal/snail" class="md-crosslink " data-show-preview="true">snails</a>), among many other groups. The <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="Tertiary" href="https://www.britannica.com/dictionary/Tertiary" data-type="EB">Tertiary</a> Period saw huge alterations in Earth’s systems and the development of the ecological and climatic conditions that characterize the modern world. The end of the Tertiary is characterized by the growth of glaciers in the Northern Hemisphere and the emergence of <a href="https://www.britannica.com/animal/primate-mammal" class="md-crosslink " data-show-preview="true">primates</a> that later gave rise to modern <a href="https://www.britannica.com/science/human-evolution" class="md-crosslink " data-show-preview="true">humans</a> (<em>Homo sapiens</em>), <a href="https://www.britannica.com/animal/chimpanzee" class="md-crosslink " data-show-preview="true">chimpanzees</a> (<em>Pan troglodytes</em>), and other living great <a href="https://www.britannica.com/animal/ape" class="md-crosslink " data-show-preview="true">apes</a>.</p><span class="marker MOD3 mod-inline"></span><span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">The name Tertiary was introduced by Italian geologist <a href="https://www.britannica.com/biography/Giovanni-Arduino" class="md-crosslink " data-show-preview="true">Giovanni Arduino</a> in 1760. Arduino devised a stratigraphic system in which <a href="https://www.britannica.com/science/sedimentary-rock" class="md-crosslink " data-show-preview="true">sedimentary rocks</a> containing <a href="https://www.britannica.com/science/fossil" class="md-crosslink " data-show-preview="true">fossils</a> were called “tertiary” rocks to distinguish them from <a href="https://www.britannica.com/science/igneous-rock" class="md-crosslink " data-show-preview="true">igneous</a> and <a href="https://www.britannica.com/science/metamorphic-rock" class="md-crosslink " data-show-preview="true">metamorphic</a> rocks present in the cores of mountain ranges (“primary” rocks), the <a href="https://www.britannica.com/science/shale" class="md-crosslink " data-show-preview="true">shales</a> and <a href="https://www.britannica.com/science/limestone" class="md-crosslink " data-show-preview="true">limestones</a> of Europe (“secondary” rocks), and surficial gravel (“quaternary” rocks). Although by modern standards his system appears simplistic, it did provide the initial framework upon which modern <a href="https://www.britannica.com/science/stratigraphy-geology" class="md-crosslink " data-show-preview="true">stratigraphy</a> is based.</p><span class="marker MOD4 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref69991"> <h2 class="h1">Tertiary environment</h2> <section data-level="2" id="ref69992"> <h2 class="h2"><span id="ref586121"></span><a href="https://www.britannica.com/science/paleogeography" class="md-crosslink " data-show-preview="true">Paleogeography</a></h2> <span class="marker PREMOD5 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="1702" data-asm-type="image"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/11/811-004-A82F76A6/Distribution-landmasses-regions-seas-ocean-basins-currents.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/588461/1702"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/11/811-004-A82F76A6/Distribution-landmasses-regions-seas-ocean-basins-currents.jpg"><img src="https://cdn.britannica.com/11/811-004-A82F76A6/Distribution-landmasses-regions-seas-ocean-basins-currents.jpg?w=300" alt="Tertiary paleogeography" data-width="527" data-height="349" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/11/811-004-A82F76A6/Distribution-landmasses-regions-seas-ocean-basins-currents.jpg" data-href="/media/1/588461/1702">Tertiary paleogeography</a><span>Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during early Tertiary time. Included in the paleogeographic reconstruction are cold and warm ocean currents. The present-day coastlines and tectonic boundaries of the configured continents are shown in the inset at the lower right.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph"><span id="ref3866"></span>The present-day <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="configuration" href="https://www.britannica.com/dictionary/configuration" data-type="EB">configuration</a> of the <a href="https://www.britannica.com/science/continent" class="md-crosslink " data-show-preview="true">continents</a> and <a href="https://www.britannica.com/science/ocean" class="md-crosslink " data-show-preview="true">oceans</a> on <a href="https://www.britannica.com/place/Earth" class="md-crosslink " data-show-preview="true">Earth</a> is the result of a complex sequence of events involving the growth and rearrangement of Earth’s <a href="https://www.britannica.com/science/plate-tectonics" class="md-crosslink " data-show-preview="true">tectonic plates</a> that began almost 200 million years ago. By the beginning of the Tertiary, the supercontinent of <a href="https://www.britannica.com/place/Pangea" class="md-crosslink " data-show-preview="true">Pangea</a> had been fragmenting for more than 100 million years, and the geometry of the continents and oceans had assumed an essentially modern aspect with several notable exceptions. The fragmentation and dispersal of the Southern Hemisphere supercontinent known as <span id="ref992101"></span><a href="https://www.britannica.com/place/Gondwana-supercontinent" class="md-crosslink " data-show-preview="true">Gondwana</a>, which had begun in the early part of the <a href="https://www.britannica.com/science/Mesozoic-Era" class="md-crosslink " data-show-preview="true">Mesozoic Era</a> (252 million to 66 million years ago), continued into the <a href="https://www.britannica.com/science/Cenozoic-Era" class="md-crosslink " data-show-preview="true">Cenozoic</a>. Australia began to separate from <a href="https://www.britannica.com/place/Antarctica" class="md-crosslink autoxref " data-show-preview="true">Antarctica</a> roughly 55 million to 56 million years ago during the late <a href="https://www.britannica.com/science/Paleocene-Epoch" class="md-crosslink " data-show-preview="true">Paleocene Epoch</a>. The initial subsidence of the South Tasman Rise, which occurred about 35 million years ago during the late <a href="https://www.britannica.com/science/Eocene-Epoch" class="md-crosslink " data-show-preview="true">Eocene Epoch</a>, resulted in a shallow but inexorably widening oceanic connection between the Indian and Pacific oceans. It was this progressive separation of the two continents that led to the development of the <span id="ref992099"></span><a href="https://www.britannica.com/place/Antarctic-Circumpolar-Current" class="md-crosslink " data-show-preview="true">Antarctic Circumpolar Current</a>, a current that sweeps around Antarctica and thermally isolates it from the effects of warmer waters and <a href="https://www.britannica.com/science/climate-meteorology" class="md-crosslink " data-show-preview="true">climates</a> to the north. This current was strengthened further and assumed its modern form as Antarctica and <a href="https://www.britannica.com/place/South-America" class="md-crosslink autoxref " data-show-preview="true">South America</a> separated and thus formed the <span id="ref992098"></span><a href="https://www.britannica.com/place/Drake-Passage" class="md-crosslink " data-show-preview="true">Drake Passage</a>. There is much debate over when this opening actually occurred. Some experts state that the Drake Passage opened as early as the Eocene about 41 million years ago, whereas others maintain that this event took place as late as the boundary between the <a href="https://www.britannica.com/science/Oligocene-Epoch" class="md-crosslink " data-show-preview="true">Oligocene</a> and <a href="https://www.britannica.com/science/Miocene-Epoch" class="md-crosslink " data-show-preview="true">Miocene epochs</a> about 23 million years ago.</p><div class="module-spacing"> </div><span class="marker MOD5 mod-inline"></span><span class="md-raw-html"><div class="md-drag md-table-wrapper"><table summary="Major Paleogene paleogeographic events"><thead><tr><th colspan="3"> Major Paleogene paleogeographic events* </th></tr></thead><tfoot><tr><td colspan="3"> *Listed are those paleogeographic events that affected global ocean circulation and certain climatic and faunal and floral migration patterns.<br> **Mya = millions of years ago. </td></tr></tfoot><tbody><tr class="table-header"> <th scope="col"> age </th> <th scope="col"> time** </th> <th scope="col"> paleogeographic events </th> </tr><tr> <th scope="row"> Middle Oligocene </th> <td> 30 mya </td> <td> Isolation of Antarctica completed after further subsidence of South Tasman Rise. </td> </tr><tr> <th scope="row"> Late Eocene and<br> Early Oligocene </th> <td> c. 35–33 mya </td> <td> Tethys severely restricted in the eastern part because of uplift of the Himalayas. </td> </tr><tr> <th scope="row"> Late Eocene </th> <td> c. 35–34 mya </td> <td> Subsidence of South Tasman Rise created shallow connection between Indian and Pacific oceans. </td> </tr><tr> <th scope="row"> Late Eocene </th> <td> c. 38 mya </td> <td> Iceland-Faeroe sill sank below sea level for the first time. </td> </tr><tr> <th scope="row"> Late Eocene </th> <td> 40–37 mya </td> <td> Tethys was partially restricted north and east of the Indian Plate. </td> </tr><tr> <th scope="row"> Late Eocene </th> <td> c. 41 mya </td> <td> Shallow connection between the South Pacific and Atlantic developed at Drake Passage. </td> </tr><tr> <th scope="row"> Middle Eocene </th> <td> 50–40 mya </td> <td> India collided with Asia. Himalayan uplift began. </td> </tr><tr> <th scope="row"> Early Eocene </th> <td> c. 55 mya </td> <td> Separation of Greenland and Scandinavia and the formation of the Norwegian–Greenland Sea began. </td> </tr><tr> <th scope="row"> Early Eocene to<br> Late Eocene </th> <td> 56–34 mya </td> <td> Greenland and Svalbard separated and higher-latitude water became available in North Atlantic. </td> </tr><tr> <th scope="row"> Early Eocene </th> <td> 56–55 mya </td> <td> Complete separation of Australia and Antarctica. Australia began northward drift. </td> </tr><tr> <th scope="row"> Early Paleocene </th> <td> c. 63–61 mya </td> <td> Seafloor spreading began to open the Labrador Sea. </td> </tr></tbody></table></div> </span> <span class="marker PREMOD6 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="1701" data-asm-type="image"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/13/813-004-10B408EB/Cenozoic-migration-routes-barriers.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/588461/1701"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/13/813-004-10B408EB/Cenozoic-migration-routes-barriers.jpg"><img src="https://cdn.britannica.com/13/813-004-10B408EB/Cenozoic-migration-routes-barriers.jpg?w=300" alt="Cenozoic migration routes" data-width="638" data-height="335" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/13/813-004-10B408EB/Cenozoic-migration-routes-barriers.jpg" data-href="/media/1/588461/1701">Cenozoic migration routes</a><span>Principal Cenozoic faunal migration routes and barriers.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">The <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="collision" href="https://www.britannica.com/dictionary/collision" data-type="EB">collision</a> of <span id="ref992100"></span><a href="https://www.britannica.com/place/India" class="md-crosslink " data-show-preview="true">India</a> and southern Asia began between 50 million and 40 million years ago, during the Eocene Epoch, and continues today. The collision produced two main geologic results. First, it began to block the westward-flowing <span id="ref992102"></span><a href="https://www.britannica.com/place/Tethys-Sea" class="md-crosslink " data-show-preview="true">Tethys seaway</a> near the <a href="https://www.britannica.com/place/Equator" class="md-crosslink " data-show-preview="true">Equator</a>, a process completed with the junction of Africa and Asia near present-day Iran roughly 16 million to 14 million years ago. Second, the creation of the <a href="https://www.britannica.com/place/Himalayas" class="md-crosslink " data-show-preview="true">Himalayas</a> and the <a href="https://www.britannica.com/place/Plateau-of-Tibet" class="md-crosslink " data-show-preview="true">Plateau of Tibet</a>, which resulted from the collision, altered global climates by changing patterns of <a href="https://www.britannica.com/science/weathering-geology" class="md-crosslink " data-show-preview="true">weathering</a> (and thus the transfer rate of <a href="https://www.britannica.com/science/carbon-chemical-element" class="md-crosslink " data-show-preview="true">carbon</a> to the <a href="https://www.britannica.com/science/atmosphere" class="md-crosslink " data-show-preview="true">atmosphere</a>) as well as <a href="https://www.britannica.com/science/wind" class="md-crosslink " data-show-preview="true">wind circulation</a>. India’s collision with southern Asia also altered patterns of oceanic productivity by increasing erosion and thus nutrient runoff to the <a href="https://www.britannica.com/place/Indian-Ocean" class="md-crosslink autoxref " data-show-preview="true">Indian Ocean</a>.</p><span class="marker MOD6 mod-inline"></span> <span class="marker PREMOD7 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="614" data-asm-type="image"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/10/6010-050-56184E94/Mediterranean-Sea.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/588461/614"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/10/6010-050-56184E94/Mediterranean-Sea.jpg"><img src="https://cdn.britannica.com/10/6010-050-56184E94/Mediterranean-Sea.jpg?w=300" alt="Mediterranean Sea" data-width="1600" data-height="880" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/10/6010-050-56184E94/Mediterranean-Sea.jpg" data-href="/media/1/588461/614">Mediterranean Sea</a><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph"><span id="ref"></span>The present-day <span id="ref586122"></span><a href="https://www.britannica.com/place/Mediterranean-Sea" class="md-crosslink " data-show-preview="true">Mediterranean Sea</a> is a geologically recent descendant of a portion of the Tethys seaway. About six million years ago, during the <a href="https://www.britannica.com/science/Messinian-Stage" class="md-crosslink " data-show-preview="true">Messinian Age</a>, the western remnant of the Tethys seaway was subject to a brief <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="paroxysm" href="https://www.merriam-webster.com/dictionary/paroxysm" data-type="MW">paroxysm</a>, known as the Messinian salinity crisis, that lasted approximately 270,000 years and saw the entire basin virtually isolated from the <a href="https://www.britannica.com/science/ocean" class="md-crosslink autoxref " data-show-preview="true">world ocean</a>. The basin experienced severe desiccation and the precipitation of vast deposits of <a href="https://www.britannica.com/science/evaporite" class="md-crosslink " data-show-preview="true">evaporites</a> (such as <a href="https://www.britannica.com/science/salt/Occurrence#ref53234" class="md-crosslink " data-show-preview="true">salt</a> and <a href="https://www.britannica.com/science/gypsum" class="md-crosslink " data-show-preview="true">gypsum</a>) up to several kilometres in thickness. The <a href="https://www.britannica.com/place/Atlantic-Ocean" class="md-crosslink autoxref " data-show-preview="true">Atlantic Ocean</a> subsequently refilled the basin from the west at the beginning of the <a href="https://www.britannica.com/science/Zanclean-Stage" class="md-crosslink " data-show-preview="true">Zanclean Age</a>. Geologic evidence suggests that water rushing through a channel cut near Gibraltar filled some 90 percent of the Mediterranean Sea within two years. Some scientists <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="contend" href="https://www.britannica.com/dictionary/contend" data-type="EB">contend</a> that sea levels may have risen 10 metres (about 33 feet) per day within the basin during the period of peak flow. The Mediterranean basin has undergone significant geologic evolution during the most recent five million years. About one million years ago this part of the Tethys was transformed into the Mediterranean Sea by the elevation of the Gibraltar <a href="https://www.britannica.com/science/sill" class="md-crosslink " data-show-preview="true">sill</a>. Consequently, the Mediterranean basin became isolated from deep oceanic bottom waters, and the present-day pattern of circulation developed.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=august-2024">Subscribe</a> </div> </div> </div> </DIV></div><span class="marker MOD7 mod-inline"></span> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">In the Northern Hemisphere the fragmentation of the northern supercontinent of <a href="https://www.britannica.com/place/Laurasia" class="md-crosslink " data-show-preview="true">Laurasia</a>, which occurred as the result of the separation of <span id="ref586123"></span><a href="https://www.britannica.com/place/Eurasia" class="md-crosslink " data-show-preview="true">Eurasia</a> from <a href="https://www.britannica.com/place/North-America" class="md-crosslink autoxref " data-show-preview="true">North America</a> and Greenland, was accomplished with the final opening of the Norwegian-Greenland Sea about 55 million years ago during the Eocene <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="Epoch" href="https://www.britannica.com/dictionary/Epoch" data-type="EB">Epoch</a>. (The seaway between the two landmasses was open at various times during the Jurassic and Cretaceous periods.) Prior to the Eocene, the Greenland-Scotland Ridge formed the Thulean <a href="https://www.britannica.com/science/land-bridge" class="md-crosslink " data-show-preview="true">Land Bridge</a>, a continental connection that allowed the exchange of terrestrial <a href="https://www.britannica.com/animal/mammal" class="md-crosslink " data-show-preview="true">mammals</a> between western Eurasia and eastern North America. The subsidence of this ridge during the early Eocene allowed the exchange of surface water between the Arctic and Atlantic oceans. The termination of the Thulean land connection led to the development of separate patterns of evolution among terrestrial <a href="https://www.britannica.com/animal/vertebrate" class="md-crosslink " data-show-preview="true">vertebrates</a> in Europe and North America (<em>see</em> <a href="https://www.britannica.com/science/evolution-scientific-theory/Mechanical-isolation#ref49891" class="md-crosslink " data-show-preview="true">evolution: Geographic speciation</a>).</p><span class="marker MOD8 mod-inline"></span> <span class="marker PREMOD9 mod-inline"></span><p class="topic-paragraph">On the Eurasian continent itself, the <span id="ref586124"></span>Ural Trough (or Turgai Strait), a marine seaway that linked the Tethys with the Arctic region but also <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="constituted" href="https://www.merriam-webster.com/dictionary/constituted" data-type="MW">constituted</a> a barrier to the east-west migration of terrestrial faunas, was terminated by regional uplift some 29 million years ago during the Oligocene. The resulting immigration of Eurasian land animals into western Europe, and the consequent changes that occurred in terrestrial vertebrates, is known among vertebrate paleontologists as the <span id="ref586125"></span>Grande Coupure (French: “Big Break”).</p><div class="one-good-fact-module"> </div><span class="marker MOD9 mod-inline"></span> <span class="marker PREMOD10 mod-inline"></span><p class="topic-paragraph"><span id="ref3865"></span>The <span id="ref586126"></span><a href="https://www.britannica.com/place/Beringia" class="md-crosslink " data-show-preview="true">Bering Land Bridge</a>, which united Siberia and Alaska, served as a second connection between Eurasia and North America. This link seems to have been <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="breached" href="https://www.merriam-webster.com/dictionary/breached" data-type="MW">breached</a> by the Arctic and Pacific oceans between five and seven million years ago, allowing the transit of cold water currents and marine faunas between the Pacific and Atlantic oceans. The Atlantic and Pacific were also linked by the <span id="ref586127"></span>Central American seaway in the area of present-day <a href="https://www.britannica.com/place/Costa-Rica" class="md-crosslink autoxref " data-show-preview="true">Costa Rica</a> and Panama. This seaway, <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="extant" href="https://www.merriam-webster.com/dictionary/extant" data-type="MW">extant</a> since the first half of the Cretaceous Period, prevented the interchange of terrestrial fauna between North and South America; however, for a brief interlude during the Paleocene, a land connection may have existed between North and South America across the volcanic archipelago of the <a href="https://www.britannica.com/place/Greater-Antilles" class="md-crosslink " data-show-preview="true">Greater Antillean</a> arc, and some scholars have argued that land bridges between the two continents may have existed for short periods during the Late Cretaceous and again during the late Miocene. The seaway was closed by the elevation of the Central American <span id="ref586128"></span><a href="https://www.britannica.com/science/isthmus" class="md-crosslink " data-show-preview="true">isthmus</a> between 5.5 million and 3 million years ago. This event had two significant geologic results. First, the emergence of the isthmus permitted a major migration in land mammal faunas between North and South America—the so-called Great American Interchange—which allowed ground <a href="https://www.britannica.com/animal/sloth/Two-toed-sloths#ref218684" class="md-crosslink " data-show-preview="true">sloths</a> and other South American immigrants to move into North America as far as California, the <a href="https://www.britannica.com/place/Great-Plains" class="md-crosslink autoxref " data-show-preview="true">Great Plains</a>, and Florida. In addition, some North American mammals (such as cats, horses, elephants, and camels) migrated as far south as Patagonia. Second, the emergence of the isthmus deflected the westward-flowing North Equatorial Current toward the north and <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="enhanced" href="https://www.merriam-webster.com/dictionary/enhanced" data-type="MW">enhanced</a> the northward-flowing <a href="https://www.britannica.com/place/Gulf-Stream" class="md-crosslink " data-show-preview="true">Gulf Stream</a>. This newly invigorated current carried warm, salty waters into high northern latitudes, which contributed to increased rates of <a href="https://www.britannica.com/science/vaporization" class="md-crosslink " data-show-preview="true">evaporation</a> over the oceans and greater <a href="https://www.britannica.com/science/precipitation" class="md-crosslink " data-show-preview="true">precipitation</a> over the region of eastern Canada and Greenland. This pattern eventually led to the formation and development of the polar ice cap in the Northern Hemisphere between 4 million and 2.5 million years ago. Deflection of the Equatorial Current also changed circulation patterns throughout the Caribbean, <a href="https://www.britannica.com/place/Gulf-of-Mexico" class="md-crosslink autoxref " data-show-preview="true">Gulf of Mexico</a>, and western North Atlantic, which may have altered patterns of oceanic productivity in the region, resulting in significant evolutionary changes (extinctions and originations) in marine faunas.</p><span class="marker MOD10 mod-inline"></span><span class="md-raw-html"><div class="md-drag md-table-wrapper"><table summary="Major Neogene paleogeographic events"><thead><tr><th colspan="3"> Major Neogene paleogeographic events* </th></tr></thead><tfoot><tr><td colspan="3"> *Listed are those paleogeographic events that affected global ocean circulation and certain climatic and faunal and floral migration patterns.<br> **Mya = millions of years ago. </td></tr></tfoot><tbody><tr class="table-header"> <th scope="col"> age </th> <th scope="col"> time** </th> <th scope="col"> paleogeographic events </th> </tr><tr> <th scope="row"> Pleistocene </th> <td> c. 1 mya </td> <td> Uplift of Gibraltar sill and development of present-day Mediterranean circulation patterns (surface water inflow, deep water outflow). </td> </tr><tr> <th scope="row"> Middle Pliocene </th> <td> 3 mya </td> <td> Uplift of the Isthmus of Panama, joining North and South America. </td> </tr><tr> <th scope="row"> Early Pliocene </th> <td> c. 5 mya </td> <td> Opening of the Strait of Gibraltar. </td> </tr><tr> <th scope="row"> Late Miocene </th> <td> c. 5.5 mya </td> <td> Closure of the Betic and Riffian (Moroccan) corridor, isolation of western Tethyan Sea from global ocean circulation, and evaporation of the basin. </td> </tr><tr> <th scope="row"> Middle Miocene </th> <td> c. 13 mya </td> <td> Final severance of the Tethys and Paratethys (epeiric continental seaway in southwestern Eurasia). </td> </tr><tr> <th scope="row"> Early Miocene </th> <td> c. 18 mya </td> <td> Junction of Africa and Eurasia. </td> </tr></tbody></table></div> </span> </section> </section><span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-simplify-root"></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article> </div> </div> </div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":1,"pagesTotal":9,"pageId":588461,"pageLength":1699,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-133/js/libs/jquery-3.5.0.min.js?v=3.133.48"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-133/dist/topic-page.js?v=3.133.48' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"D","adLeg":"C","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"PAGINATED","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":true,"hasAiTopQuestions":false,"hasSimplifyButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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