Query: The new research showed that [oxygen isotopes in foraminifera] can change

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Pleistocene <=SEP=> The Pleistocene ( -LSB- pronˈplaɪstəˌsiːn , _ - toʊ - -RSB- , often colloquially referred to as the Ice Age ) is the geological epoch which lasted from about 2,588,000 to 11,700 years ago , spanning the world 's most recent period of repeated glaciations . The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology .   The Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era . In the ICS timescale , the Pleistocene is divided into four stages or ages , the Gelasian , Calabrian , Ionian and Tarantian . All of these stages were defined in southern Europe . In addition to this international subdivision , various regional subdivisions are often used .   Before a change finally confirmed in 2009 by the International Union of Geological Sciences , the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present ( BP ) , as opposed to the currently accepted 2.588 million years BP : publications from the preceding years may use either definition of the period .

Radiocarbon dating <=SEP=> Radiocarbon dating ( also referred to as carbon dating or carbon-14 dating ) is a method for determining the age of an object containing organic material by using the properties of radiocarbon , a radioactive isotope of carbon .   The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists . Libby received the Nobel Prize in Chemistry for his work in 1960 . The radiocarbon dating method is based on the fact that radiocarbon is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen . The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide , which is incorporated into plants by photosynthesis ; animals then acquire by eating the plants . When the animal or plant dies , it stops exchanging carbon with its environment , and from that point onwards the amount of it contains begins to decrease as the undergoes radioactive decay . Measuring the amount of in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died . The older a sample is , the less there is to be detected , and because the half-life of ( the period of time after which half of a given sample will have decayed ) is about 5,730 years , the oldest dates that can be reliably measured by this process date to around 50,000 years ago , although special preparation methods occasionally permit accurate analysis of older samples .   The idea behind radiocarbon dating is straightforward , but years of work were required to develop the technique to the point where accurate dates could be obtained . Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years . The resulting data , in the form of a calibration curve , is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample 's calendar age . Other corrections must be made to account for the proportion of in different types of organisms ( fractionation ) , and the varying levels of throughout the biosphere ( reservoir effects ) . Additional complications come from the burning of fossil fuels such as coal and oil , and from the above-ground nuclear tests done in the 1950s and 1960s . Because the time it takes to convert biological materials to fossil fuels is substantially longer than the time it takes for its to decay below detectable levels , fossil fuels contain almost no , and as a result there was a noticeable drop in the proportion of in the atmosphere beginning in the late 19th century . Conversely , nuclear testing increased the amount of in the atmosphere , which attained a maximum in 1963 of almost twice what it had been before the testing began .   Measurement of radiocarbon was originally done by beta-counting devices , which counted the amount of beta radiation emitted by decaying atoms in a sample . More recently , accelerator mass spectrometry has become the method of choice ; it counts all the atoms in the sample and not just the few that happen to decay during the measurements ; it can therefore be used with much smaller samples ( as small as individual plant seeds ) , and gives results much more quickly . The development of radiocarbon dating has had a profound impact on archaeology . In addition to permitting more accurate dating within archaeological sites than previous methods , it allows comparison of dates of events across great distances . Histories of archaeology often refer to its impact as the `` radiocarbon revolution '' . Radiocarbon dating has allowed key transitions in prehistory to be dated , such as the end of the last ice age , and the beginning of the Neolithic and Bronze Age in different regions .

Proxy (climate) <=SEP=> In the study of past climates ( `` paleoclimatology '' ) , climate proxies are preserved physical characteristics of the past that stand in for direct meteorological measurements and enable scientists to reconstruct the climatic conditions over a longer fraction of the Earth 's history . Reliable global records of climate only began in the 1880s , and proxies provide the only means for scientists to determine climatic patterns before record-keeping began .   Examples of proxies include ice cores , tree rings , sub-fossil pollen , boreholes , corals , lake and ocean sediments , and carbonate speleothems . The character of deposition or rate of growth of the proxies ' material has been influenced by the climatic conditions of the time in which they were laid down or grew . Chemical traces produced by climatic changes , such as quantities of particular isotopes , can be recovered from proxies . Some proxies , such as gas bubbles trapped in ice , enable traces of the ancient atmosphere to be recovered and measured directly to provide a history of fluctuations in the composition of the Earth 's atmosphere . To produce the most precise results , systematic cross-verification between proxy indicators is necessary for accuracy in readings and record-keeping .   Proxies can be combined to produce temperature reconstructions longer than the instrumental temperature record and can inform discussions of global warming . The distribution of proxy records , just like the instrumental record , is not at all uniform , with more records in the northern hemisphere .

Speleothem <=SEP=> Speleothems ( -LSB- pronˈspiːliːəθɛm -RSB- Ancient Greek : `` cave deposit '' ) -- commonly known as a cave formations -- are secondary mineral deposits formed in a cave . Speleothems typically form in limestone or dolostone solutional caves . The term `` speleothem '' as first introduced by Moore ( 1952 ) , is derived from the Greek words spēlaion `` cave '' + théma `` deposit '' . The definition of `` speleothem '' in most publications , specifically excludes secondary mineral deposits in mines , tunnels and on man-made structures . Hill and Forti more concisely defined `` secondary minerals '' which create speleothems in caves as ;  A `` secondary '' mineral is one which is derived by a physicochemical reaction from a primary mineral in bedrock or detritus and/or deposited because of a unique set of conditions in a cave ; i.e. , the cave environment has influenced the mineral 's deposition .