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40-481: The EECO lasted from about 54 to 49 Ma. The EECO's onset is signified by a major geochemical enrichment in isotopically light carbon, commonly known as a negative δ C excursion, that demarcates the hyperthermal Eocene Thermal Maximum 3 (ETM3). Following some climate models , the EECO was marked by an extremely high global mean surface temperature , which has been estimated to be anywhere between 23.2 and 29.7 °C, with

80-590: A MAP of 1100 ± 299 mm, notably drier than the region was during the Palaeocene-Eocene Thermal Maximum . Sea surface temperatures (SSTs) off of Seymour Island were ~15 °C. The high elevation areas of Asia, Africa , and Antarctica saw elevation dependent warming (EDW), while those in North America and India saw elevation dependent cooling (EDC). The latitudinal climate gradient is generally believed to have been smaller, which

120-482: A biodiversity hotspot from which newly evolved lineages of temperate-adapted plants radiated from following the end of the EECO. The climate was warm enough to allow palms and palm beetles to inhabit upland regions of British Columbia and Washington. Ellesmere Island became inhabited by basal primatomorphs. The leadup to the EECO was marked by an increase in mammal diversity in Wyoming's Bighorn Basin. Northern Yakutia

160-469: A dependence on zoophilous pollination. Genetic evidence indicates a major radiation of phasmatodeans occurred during the KTR, likely in response to a coeval radiation of enantiornitheans and other visual predators. Ants likewise underwent massive increase in diversity as part of the KTR. Similarly, bee pollinator diversification strongly correlates with angiosperm flower appearance and specialization during

200-584: A great development after the extinction of the end of the Cretaceous will be strongly affected by the climatic warming of the Paleogene. Temperature increases and induced climate changes modify the flora and the quantities of fodder available for herbivores. This is how a large number of groups of mammals appear at the beginning of the Eocene , about 56 million years ago: Even if the hyperthermal events of

240-607: A sudden warming of the planet on a geologic time scale . The consequences of this type of event are the subject of numerous studies because they can constitute an analogue of current global warming . The first event of this type was described in 1991 from a sediment core extracted from a drilling of the Ocean Drilling Program (ODP) carried out in Antarctica in the Weddell Sea . This event occurs at

280-523: A switch from dextral to sinistral coiling across the EECO. The euryhaline dinoflagellate Homotryblium became superabundant at the site of Waipara in New Zealand during the early and middle EECO, reflecting the occurrence of significant stratification of surficial waters as well as increased salinity. The EECO caused an increase in chert deposition by way of basin–basin fractionation by deep-sea circulation, causing increased silica concentrations in

320-403: Is recorded in southeastern Australian sediments. The central Tethys in what is now northeastern Italy was a hotspot of coral diversity, with its mesophotic deltaic environment acting as a refugium. At Shatsky Rise, the planktonic foraminifera Morozovella and Chiloguembelina declined in abundance. Acarinina became the dominant planktonic foraminifer in this locality. Morozovella underwent

360-594: The Angiosperm Terrestrial Revolution ( ATR ) by authors who consider it to have lasted into the Palaeogene , describes the intense floral diversification of flowering plants ( angiosperms ) and the coevolution of pollinating insects , as well as the subsequent faunal radiation of frugivorous , nectarivorous and insectivorous avians , mammals , lissamphibians , squamate reptiles and web -spinning spiders during

400-671: The Middle to Late Cretaceous , from around 125 Mya to 80 Mya. Alternatively, according to Michael Benton , the ATR is proposed to have lasted from 100 Ma, when the first highly diverse angiosperm leaf floras are known, to 50 Ma, during the Early Eocene Climatic Optimum , by which point most crown lineages of angiosperms had evolved . Molecular clock analyses of angiosperm evolution suggest that crown group angiosperms may have diverged up to 100 million years before

440-595: The benthic foraminifera had gone through the Cretaceous-Tertiary extinction that occurred around 66 million years ago without difficulty, the hyperthermic event of the PETM, 10 million years later, decimated them with the disappearance of 30 to 50% of existing species . The warming of surface waters also leads to eutrophication of the marine environment which leads to a rapid increase by positive feedback of CO 2 emissions. Mammals that experienced

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480-399: The Cretaceous in the aftermath of Pangaea 's breakup in the preceding Jurassic period, which enhanced the hydrological cycle and promoted the expansion of temperate climatic zones, fuelling radiations of angiosperms. Among mammals, enhanced tectonic activity generated diversity increases by increasing montane habitats, which promote increased diversity in hot climates. Another cause of

520-618: The Cretaceous. Although angiosperm diversity drastically grew over the Cretaceous, this did not necessarily translate to ecological dominance, which they only achieved in the Early Cenozoic. Angiosperms responded to increasing coevolution with frugivores by enlarging the sizes of their fruits, which peaked during the Early Eocene. Before Lloyd et al.' s 2008 paper described the KTR, it had been widely accepted in paleontology that new families of dinosaurs evolved during

560-557: The EECO by enabling high rates of organic carbon burial in lacustrine settings. The EECO was preceded by a major long-term warming trend in the Late Palaeocene and Early Eocene . It was initiated by a series of intense hyperthermal events in the Early Eocene, including Eocene Thermal Maximum 2 (ETM2) and ETM3. The emplacement of the Pana Formation, a volcanic rock formation in southern Tibet that may represent

600-583: The EECO fostered extensive floral diversification and increased habitat complexity in North American terrestrial biomes. The hot, humid conditions of the EECO may have facilitated the evolution of epiphytic bryophytes, with the oldest member of Lejeuneaceae being described from fossils from the Cambay amber dating back to the EECO. The Okanagan Highlands in British Columbia and Washington became

640-643: The EECO has been used as an analogue for high-end projections of the Earth's future climate that would result from humanity's burning of fossil fuels. Based on the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario, by 2150 CE, the climates across much of the world would resemble conditions during the EECO. One scenario of Lee et. al. (2021) suggests that conditions comparable to EECO could occur by 2300 CE. Hyperthermal event A hyperthermal event corresponds to

680-485: The Middle Cretaceous Hothouse (MKH) benefitted angiosperms, which were able to survive hot and dry environments, and the increased fire activity helped to enhance diversification of angiosperms. Angiosperms enabled more frequent fires than gymnosperms, and they also recovered more quickly from fires than gymnosperms did. This created a feedback loop that advantaged angiosperms over gymnosperms during

720-621: The Middle to Late Cretaceous, including the euhadrosaurs , neoceratopsians , ankylosaurids , pachycephalosaurs , carcharodontosaurines , troodontids , dromaeosaurs and ornithomimosaurs . However, the authors of the paper have suggested that the apparent "new diversification" of dinosaurs during this time is due to sampling biases in the fossil record, and better preserved fossils in Cretaceous age sediments than in earlier Triassic or Jurassic sediments. However, later studies still suggest

760-483: The North Atlantic which in turn resulted in direct precipitation of silica as well as its absorption by clay minerals. The Equatorial Pacific displays extensive chert deposits laid down during the EECO. The EECO was also marked by enhanced glauconite deposition. Because the p CO 2 values of the EECO could potentially be reached if anthropogenic greenhouse gas emissions continue unabated for three centuries,

800-579: The PETM event remains the most studied of the hyperthermic events. Other hyperthermic events occurred at the end of most Quaternary glaciations . Probably the most notable of these is the abrupt warming marking the end of the Younger Dryas , which saw an average annual temperature rise of several degrees in less than a century. While the consequences of these hyperthermic events are now well studied and known, their causes are still debated. Two main tracks, possibly complementary, are mentioned for

840-555: The Paleogene appear extremely brutal on the geologic time scale (in a range of a few thousand years for an increase of the order of 5 °C), they remain significantly longer than the durations envisaged in the current models of global warming of anthropogenic origin. The various studies of hyperthermal events insist on the phenomena of positive feedbacks which, after the onset of a warming, accelerate it considerably. Cretaceous Terrestrial Revolution The Cretaceous Terrestrial Revolution (abbreviated KTR ), also known as

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880-495: The angiosperm radiation, but this proved to be an evolutionary dead end in the long run and the group went extinct. The so-called "golden age" of neuropterans during the Middle Mesozoic, when gymnosperms dominated the flora, ended with the KTR and its reshaping of the terrestrial environment. The KTR may have supercharged the contemporary Mesozoic Marine Revolution (MMR) by enhancing weathering and erosion, accelerating

920-606: The boundary of the Paleocene and Eocene epochs approximately 56 million years ago. It is now called the Paleocene-Eocene Thermal Maximum (PETM). During this event, the temperature of the oceans increased by more than 5 °C in less than 10,000 years. Since this discovery, several other hyperthermal events have been identified in this lower part of the Paleogene geological period : But

960-456: The continents. The δ13C ratios of the carbon isotope contents of the carbonates constituting the shells of the benthic foraminifera have shown an upheaval in the oceanic circulations during the PETM under the effect of global warming. This change took place over a few thousand years. The return to the previous situation, again by negative feedback thanks to the " CO 2 pump" of silicate weathering, took about 200,000 years. While

1000-580: The explosive angiosperm diversification was the evolution of leaf vein densities greater than 2.5–5 mm/mm , when the leaf interior transport path length of water became shorter than the leaf interior transport path length of CO 2 . This enabled greater utilisation of CO 2 and gave an evolutionary advantage to flowering plants over conifers because they could sequester more CO 2 for the same amount of water. The much greater capacity of angiosperms for assimilating CO 2 sharply increased global bioproductivity. The drying of many terrestrial ecosystems during

1040-558: The flow of limiting nutrients into the world’s oceans. For nearly the entirety of Earth's history , including most of the Phanerozoic eon, marine species diversity exceeded terrestrial species diversity, a pattern which was reversed during the Middle Cretaceous as a result of the KTR in what has been termed a biological "great divergence", named after the historical Great Divergence . This article related to

1080-449: The increase in CO 2 dissolved in seawater, the oceans are acidifying. This results in a dissolution of the carbonates; global sedimentation becomes essentially clayey. This process takes place in less than 10,000 years while it will take about 100,000 years for the carbonate sedimentation to return to its pre-PETM level mainly by CO 2 capture through greater silicate weathering on

1120-410: The initiation of these sudden warmings: Marine warming due to PETM is estimated, for all latitudes of the globe, between 4 and 5 °C for deep ocean waters and between 5 and 9 °C for surface waters. Carbon trapped in clathrates buried in high latitude sediments is released to the ocean as methane ( CH 4 ) which will quickly oxidize to carbon dioxide ( CO 2 ). As a result of

1160-482: The mean estimate being around 27.0 °C. In North America , the mean annual temperature was 23.0 °C, while the continent's overall mean annual precipitation (MAP) was about 1500 mm. The mean annual temperature range (MATR) of North America may have been as low as 47 °C or as high as 61 °C, while the MATR of Asia was anywhere from 51 to 60 °C. The Okanagan Highlands had a moist mesothermal climate, with bioclimatic analysis of

1200-558: The observed hothouse conditions of the EECO, although geochemical proxies suggest only 700-900 ppm. Stomatal density in Gingko leaves suggests p CO 2 was over twice that of preindustrial levels. Additionally, methane concentrations in the Early Eocene may have been significantly higher than in the present day. The nature of the hydrological cycle during the EECO is controversial. Evidence from German peat bogs suggests that it

1240-405: The possibility that the KTR caused a rise in dinosaur diversity. Dinosaurs contributed little to angiosperm diversification, which was instead mainly driven by coevolution with other animals, such as insects and herbivorous mammals. It has been suggested that some pterosaurs may have been seed dispersers symbiotically linked to angiosperms. A comprehensive molecular study of evolution of mammals at

Early Eocene Climatic Optimum - Misplaced Pages Continue

1280-412: The product of a supereruption , has also been proposed as a source of excess carbon flux into the atmosphere that drove the EECO. Other research attributes the elevated greenhouse gas levels to increased generation of petroleum in sedimentary basins and enhanced ventilation of marine carbon. The final phase of the Angiosperm Terrestrial Revolution occurred during the EECO. The supergreenhouse climate of

1320-760: The region yielding estimates of a mean annual temperature (MAT) of 12.7-16.6 °C, a cold month mean temperature (CMMT) of 3.5-7.9 °C, and a MAP of 103-157 cm. Clumped isotope measurements from the Green River Basin and the Bighorn Basin confirm a high seasonality of temperature, contradicting climatological predictions of an equable climate under greenhouse conditions. Lake temperatures in the Green River Formation ranged from 28 °C to 35 °C, with lacustrine photic zone euxinia being prevalent. Sediments from San Diego County, California record

1360-471: The same era. Flies , already successful pollinators before the rise of angiosperms, quickly adapted to the new hosts. Beetles became pollinators of angiosperms by the earliest part of the Late Cretaceous. Lepidopterans radiated during the KTR, though the angiosperm radiation is insufficient in and of itself to completely account for their diversification. Among one lineage of sawflies , there

1400-405: The start of the KTR, although this is possibly due to artefacts of the inabilities of molecular clock estimates to account for explosive accelerations in evolution that may have caused the extremely fast diversification of angiosperms shortly after their first appearance in the fossil record . The KTR was enabled by the dispersed positions of the continents and the formation of new oceans during

1440-523: The taxonomic level of family also showed important diversification during the KTR. Mammals have been found to have decreased in disparity during the KTR. Insect diversity overall appears to have been minimally affected by the KTR, as molecular evidence shows that the increase in diversity of pollinating insects was asynchronous with the KTR. However, Early Cretaceous angiosperms were short in stature and would have been heavily reliant on insect pollination, and fossil remains of early angiosperms suggest such

1480-459: Was a change in preferred host plants amidst the biotic reorganisation of the KTR. Not all insects were advantaged by this diversification and rearrangement of ecosystems; long-proboscid insects that were mainstays of gymnosperm-dominated ecosystems earlier in the Mesozoic underwent a major decline. Late-surviving eoblattodeans evolved long, slim bodies with long external ovipositors in response to

1520-643: Was covered in mangroves. Mongolia witnessed a humidification event that transformed it from a shrubland into a forest and significantly reducing local wildfire incidence. In South America , the EECO coincided with the Itaboraian South American Land Mammal Age . Cingulates diversified over the course of the EECO. The northern margins of the Australo-Antarctic Gulf, then located at 60-65 °S, were covered in wet-tropical lowland vegetation. Nypa pollen

1560-483: Was highly variable, with alternations between aridity and humidity. Hydroclimatic variability in the Gonjo Basin was predominantly controlled by orbital eccentricity cycles. Evidence from North America, in contrast, suggests that the hydrological cycle was enhanced during the EECO, although it remained relatively stable, unlike during the earlier hyperthermals, and that the stable hydroclimate may ultimately have ended

1600-416: Was mainly the result of a decrease in albedo differences across Earth's surface. Although SSTs are often believed to have had a shallow latitudinal temperature gradient, this is likely to be an artefact of burial-induced oxygen isotope reequilibration in fossilised benthic foraminifera. Climate modelling simulations point to a carbon dioxide concentration in the atmosphere of about 1,680 ppm to reproduce

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