According to who long term cycle is the sum of two or three short term cycles
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Changes in Earth's orbit have helped pace climatic change for millennia. Scientists are now trying to understand whether - and how - these changes remodeled the landscapes our ancient ancestors inhabited.
The idea that critical junctures in human evolution and behavioral development may have been shaped by environmental factors has been around since Darwin. Although various hypotheses and models have been proposed, refined, and/or abandoned for at least a century, the concept of environmental determinism and hominin evolution is still a hot topic today. While it is ultimately local-level environmental processes acting upon individual populations that is one of the driving forces of evolutionary change, such shifts are often framed within the context of much larger regional or global climatic trends.Direct measurements of climate components such as temperature and precipitation only exist for the last century or two. To reconstruct climate over longer time-scales, scientists indirectly measure these components by analyzing various proxies, or indicators, that are sensitive to climatic or environmental parameters and preserved in the geological record. Proxy records from marine sediment and ice cores provide the basis for much of our understanding of past climate. These long-term and relatively continuous natural archives are often used as references for comparison with local terrestrial-based paleoenvironmental reconstructions. For example, the record of oxygen and hydrogen isotope ratios preserved in glacial ice, and oxygen isotope ratios in the shells of marine organisms such as foraminifera and radiolaria, provide a record of past sea levels, ice volume, seawater temperature and global atmospheric temperature (Figures 1 & 2). Air bubbles trapped in ice cores also provide a direct record of the past chemical composition of the atmosphere, particularly CO2. Carbon isotope ratios of shells in marine cores are equally valuable for estimates of water circulation and atmospheric CO2 concentrations. Eolian dust preserved in both marine sediment and ice cores has been correlated with climate and environmental conditions in the dust's source region, specifically as a proxy for aridity. Continuous ice cores from Greenland record back to over 100,000 years ago (Bender et al. 2002), while those from Antarctica extend back to ~800,000 years ago (Lambert et al. 2008). Thus, these records are relevant to the later members of the genus Homo, such as H. erectus, H. heidelbergensis, H. neanderthalensis, and H. sapiens. Documenting a much longer timescale, marine sediment cores have been collected across the globe, and composite records have been compiled that extend beyond the Cenozoic, thus covering the entire duration of the Primate fossil record (Zachos et al. 2001).
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