Что такое орбитальные циклы

Из-за периодических изменений параметров своей орбиты Земля проходит через повторяющиеся ледниковые периоды.

В XIX веке геологи сделали неожиданное открытие: оказалось, что когда-то огромные арктические ледники наступили на сушу и накрыли почти всю Европу и Северную Америку. В частности, на оледенение этих зон указывают следующие два геологических признака. Представьте, что продвигающийся ледник действует наподобие бульдозера: он толкает перед собой грунт и обломки горных пород. Когда ледник достигает своего максимума и начинает отступать, груда оставшейся горной породы превращается в цепь холмов – это так называемые ледниковые морены. Вдобавок, при передвижении ледника движущийся (хотя и медленно) лед несет с собой куски горной породы. Если взглянуть на поверхность горной долины, образованной ледником, можно обнаружить на ней глубокие параллельные борозды. Происхождение этих царапин легко объяснить, если представить себе, что ледник с утопленной нижней частью передвигается по горной породе, действуя как напильник или наждачная бумага. Морены и царапины – яркие доказательства того, что когда-то здесь были ледники.

Вскоре после этого открытия стало ясно, что ледниковый период на Земле наступал не один раз. По-видимому, ледниковые периоды повторялись в прошлом через определенные промежутки времени. Почему так происходило, никто не мог объяснить вплоть до начала ХХ века, когда разрешить эту загадку взялся один выдающийся ученый. В своих мемуарах Милутин Миланкович рассказывает о том, как он пришел к мысли о причинах ледниковых периодов. Приятель Миланковича опубликовал сборник своих патриотических стихов, и они вместе отмечали это событие в кафе (молодые преподаватели Белградского университета могли себе позволить только кофе). Сидящему рядом богатому коммерсанту так понравились стихи, что он тут же купил десять экземпляров книги. Друзья заказали вина и стали праздновать по-настоящему. После первой бутылки Миланкович «вспомнил свои прежние достижения, которые теперь казались узкими и ограниченными». К концу третьей бутылки поэт уже собирался написать эпическую поэму, а Миланкович решил «постичь всю Вселенную и донести луч света до ее отдаленных уголков».

Во время Первой мировой войны Миланкович служил в генеральном штабе сербской армии. Он был захвачен в плен австро-венгерскими войсками и отбывал заключение в Будапеште. К счастью для Миланковича (и для науки), его коллеги из Венгерской академии наук создали ему условия для работы – под честное слово, что он не попытается сбежать. Он согласился и большую часть войны разрабатывал теорию периодичности ледниковых периодов.

Его объяснение связано с изменениями в земной орбите (теперь они называются «циклы Миланковича»). В соответствии с законом всемирного тяготения Ньютона (а также первым из законов Кеплера, описывающим траектории движения планет Солнечной системы), каждая планета вращается вокруг Солнца по эллиптической орбите. Кроме того, согласно закону сохранения момента импульса, если Земля вращается вокруг своей оси, то направление этой оси в пространстве должно оставаться неизменным. Но в реальной Солнечной системе Земля вращается вокруг Солнца не в гордом одиночестве. На нее действует притяжение Луны и других планет, и это притяжение оказывает хоть и слабое, но очень важное влияние и на земную орбиту, и на вращение Земли. Это влияние выражается трояко:

Прецессия. На самом деле земная ось не повернута всегда в одном и том же направлении – она медленно движется по круговому конусу. Этот эффект назвается «прецессия». На нем основано действие гироскопа. Когда гироскоп приходит в движение, он быстро вращается вокруг своей оси, при этом сама ось описывает конус. С земной осью происходит то же самое, причем период полного оборота составляет приблизительно 26 тысяч лет. Сейчас Земля наклонена так, что в январе (когда Земля находится ближе всего к Солнцу) северное полушарие, где расположена основная часть суши, отвернуто от Солнца. Через 13 тысяч лет ситуация изменится на противоположную: в январе северное полушарие будет повернуто к Солнцу, и январь станет в северном полушарии серединой лета.

Нутация. В дополнение к медленной прецессии Земли незначительно колеблется и угол наклона земной оси (эти колебания и называются «нутацией»). Сейчас ось наклонена на 23° к плоскости земной орбиты. Каждую 41 тысячу лет под влиянием не только Луны, но и Юпитера (далекой, но массивной планеты) угол наклона уменьшается до 22° и затем вновь возрастает до 23°.

Изменение формы орбиты. Из-за притяжения других планет с течением времени меняется и форма земной орбиты. От эллипса, вытянутого в одном направлении, она превращается в круг, затем – в эллипс, вытянутый в направлении, перпендикулярном исходному, затем – снова в круг и т. д. Этот цикл длится примерно 93 тысячи лет.

Миланкович пришел к выводу, что каждый из этих факторов влияет на количество солнечного света, полученного разными областями Земли. Например, прецессия земной оси влияет на характер зим и лет в северном полушарии (я обращаю особое внимание на северное полушарие, так как там расположена основная часть суши, и, следовательно, там находится основная часть ледников).

Миланкович понял, что с течением времени климат Земли меняется (см. Равновесие). Если количество солнечного света, которое получает северное полушарие, уменьшается, то снег с каждым годом будет все дольше оставаться на поверхности. А поскольку снег хорошо отражает свет, увеличившаяся снежная поверхность будет отражать больше солнечного света, и это приведет к дальнейшему охлаждению Земли. Значит, следующей зимой выпадет еще больше снега, еще больше увеличится площадь снежного покрова, будет отражаться еще больше солнечного света и т. д. С течением времени накопится много снега, и ледники двинутся на юг. Земля вступит в ледниковый период. В конце этого цикла, когда в северное полушарие начнет поступать больше солнечной энергии, произойдут обратные изменения – в некоторых местах лед растает, обнажатся участки почвы, хорошо поглощающей свет, Земля нагреется, и всё те же три фактора изменчивости вращения Земли приведут к тому, что ледник отступит.

Миланкович считал, что на климат на Земле оказывают влияние эти три цикла, каждый из которых связан с определенным астрономическим эффектом. Когда они усиливают друг друга, можно ожидать похолодания и наступления ледникового периода. Однако в норме эти три фактора действуют в разных направлениях и их влияние не суммируется, так что климат быстро возвращается в обычное состояние. Итак, ледниковые периоды возникают, когда три орбитальных фактора действуют в одном направлении, их эффекты складываются и подталкивают климат Земли к похолоданию. Это явление не раз повторялось в истории планеты.

За последние 3 миллиона лет было по крайней мере четыре периода масштабного оледенения, а до этого были и еще. Хочу напомнить, что последний ледниковый период достиг своего максимума примерно 18 тысяч лет назад и что время, в которое мы живем, ученые определяют как межледниковое – весьма обнадеживающее определение.

См. также:

Источник

Past and future Milankovitch cycles via VSOP model

• Graphic shows variations in five orbital elements:

Axial tilt or obliquity (ε).

Eccentricity (e).

Longitude of perihelion ( sin(ϖ) ).

Precession index ( e sin(ϖ) )

• Precession index and obliquity control insolation at each latitude:

Daily-average insolation at top of atmosphere on summer solstice () at 65° N

• Ocean sediment and Antarctic ice strata record ancient sea levels and temperatures:

Benthic forams (57 widespread locations)

Vostok ice core (Antarctica)

• Vertical gray line shows present (2000 CE)

Milankovitch cycles describe the collective effects of changes in the Earth’s movements on its climate over thousands of years. The term is named for Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he hypothesized that variations in eccentricity, axial tilt, and precession resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital forcing strongly influenced the Earth’s climatic patterns.

Similar astronomical hypotheses had been advanced in the 19th century by Joseph Adhemar, James Croll and others, but verification was difficult because there was no reliably d evidence, and because it was unclear which periods were important.

Now, materials on Earth that have been unchanged for millennia (obtained via ice, rock, and deep ocean cores) are being studied to indicate the history of Earth’s climate. Though they are consistent with the Milankovitch hypothesis, there are still several observations that the hypothesis does not explain.

Earth’s movements[edit]

The Earth’s rotation around its axis, and revolution around the Sun, evolve over due to gravitational interactions with other bodies in the Solar System. The variations are complex, but a few cycles are dominant.[1]

Circular orbit, no eccentricity

Orbit with 0.5 eccentricity, exaggerated for illustration; Earth’s orbit is only slightly eccentric

The Earth’s orbit varies between nearly circular and mildly elliptical (its eccentricity varies). When the orbit is more elongated, there is more variation in the distance between the Earth and the Sun, and in the amount of solar radiation, at different s in the year.

In addition, the rotational tilt of the Earth (its obliquity) changes slightly. A greater tilt makes the seasons more extreme. Finally, the direction in the fixed stars pointed to by the Earth’s axis changes (axial precession), while the Earth’s elliptical orbit around the Sun rotates (apsidal precession). The combined effect is that proximity to the Sun occurs during different astronomical seasons.

Milankovitch studied changes in these movements of the Earth, which alter the amount and location of solar radiation reaching the Earth. This is known as solar forcing (an example of radiative forcing). Milankovitch emphasized the changes experienced at 65° north due to the great amount of land at that latitude. Land masses change temperature more quickly than oceans, because of the mixing of surface and deep water and the fact that soil has a lower volumetric heat capacity than water.

Orbital eccentricity[edit]

The Earth’s orbit approximates an ellipse. Eccentricity measures the departure of this ellipse from circularity. The shape of the Earth’s orbit varies between nearly circular (with the lowest eccentricity of 0.000055) and mildly elliptical (highest eccentricity of 0.0679).[2] Its geometric or logarithmic mean is 0.0019. The major component of these variations occurs with a period of 413,000 years (eccentricity variation of ±0.012). Other components have 95,000-year and 125,000-year cycles (with a beat period of 400,000 years). They loosely combine into a 100,000-year cycle (variation of −0.03 to +0.02). The present eccentricity is 0.017 and decreasing.

Eccentricity varies primarily due to the gravitational pull of Jupiter and Saturn. However, the semi-major axis of the orbital ellipse remains unchanged; according to perturbation theory, which computes the evolution of the orbit, the semi-major axis is invariant. The orbital period (the length of a sidereal year) is also invariant, because according to Kepler’s third law, it is determined by the semi-major axis.

Effect on temperature[edit]

The semi-major axis is a constant. Therefore, when Earth’s orbit becomes more eccentric, the semi-minor axis shortens. This increases the magnitude of seasonal changes.[3]

The relative increase in solar irradiation at closest approach to the Sun (perihelion) compared to the irradiation at the furthest distance (aphelion) is slightly larger than four s the eccentricity. For Earth’s current orbital eccentricity, incoming solar radiation varies by 6.8%, while the distance from the Sun currently varies by only 3.4% (5.1 million km or 3.2 million mi or 0.034 au).

Perihelion presently occurs around January 3, while aphelion is around July 4. When the orbit is at its most eccentric, the amount of solar radiation at perihelion will be 23% more than at aphelion. However, the Earth’s eccentricity is always so small that the variation in solar irradiation is a minor factor in seasonal climate variation, compared to axial tilt and even compared to the relative ease of heating the larger land masses of the northern hemisphere.

Effect on lengths of seasons[edit]

Season durations[4]

The seasons are quadrants of the Earth’s orbit, marked by the two solstices and the two equinoxes. Kepler’s second law es that a body in orbit traces equal areas over equal s; its orbital velocity is highest around perihelion and lowest around aphelion. The Earth spends less near perihelion and more near aphelion. This means that the lengths of the seasons vary.

Perihelion currently occurs around January 3, so the Earth’s greater velocity shortens winter and autumn in the northern hemisphere. Summer in the northern hemisphere is 4.66 days longer than winter, and spring is 2.9 days longer than autumn.

Greater eccentricity increases the variation in the Earth’s orbital velocity. However, currently, the Earth’s orbit is becoming less eccentric (more nearly circular). This will make the seasons more similar in length.

22.1-24.5° range of Earth’s obliquity

Axial tilt (obliquity)[edit]

The angle of the Earth’s axial tilt with respect to the orbital plane (the obliquity of the ecliptic) varies between 22.1° and 24.5°, over a cycle of 41,000 years. The current tilt is 23.44°, roughly halfway between its extreme values. The tilt last reached its maximum in 8,700 BCE. It is now in the decreasing phase of its cycle, and will reach its minimum around the year 11,800 CE.

Increased tilt increases the amplitude of the seasonal cycle in insolation, providing more solar radiation in each hemisphere’s summer and less in winter. However, these effects are not uniform everywhere on the Earth’s surface. Increased tilt increases the total annual solar radiation at higher latitudes, and decreases the total closer to the equator.

The current trend of decreasing tilt, by itself, will te milder seasons (warmer winters and colder summers), as well as an overall cooling trend. Because most of the planet’s snow and ice lies at high latitude, decreasing tilt may encourage the onset of an ice age for two reasons: There is less overall summer insolation, and also less insolation at higher latitudes, which melts less of the previous winter’s snow and ice.

Axial precession[edit]

Axial precessional movement

Axial precession is the trend in the direction of the Earth’s axis of rotation relative to the fixed stars, with a period of 25,771.5 years. This motion means that eventually Polaris will no longer be the north pole star. It is caused by the tidal forces exerted by the Sun and the Moon on the solid Earth; both contribute roughly equally to this effect.

Currently, perihelion occurs during the southern hemisphere’s summer. This means that solar radiation due to (1) axial tilt inclining the southern hemisphere toward the Sun and (2) the Earth’s proximity to the Sun, both reach maximum during the southern summer and both reach minimum during the southern winter. Their effects on heating are thus additive, which means that seasonal variation in irradiation of the southern hemisphere is more extreme. In the northern hemisphere, these two factors reach maximum at opposite s of the year: The north is tilted toward the Sun when the Earth is furthest from the Sun. The two effects work in opposite directions, resulting in less extreme variations in insolation.

In 13,000 years, the north pole will be tilted toward the Sun when the Earth is at perihelion. Axial tilt and orbital eccentricity will both contribute their maximum increase in solar radiation during the northern hemisphere’s summer. Axial precession will te more extreme variation in irradiation of the northern hemisphere and less extreme variation in the south.

When the Earth’s axis is aligned such that aphelion and perihelion occur near the equinoxes, axial tilt will not be aligned with or against eccentricity.

Apsidal precession[edit]

Planets orbiting the Sun follow elliptical (oval) orbits that rotate gradually over (apsidal precession). The eccentricity of this ellipse, as well as the rate of precession, is exaggerated for visualization.

In addition, the orbital ellipse itself precesses in space, in an irregular fashion, completing a full cycle every 112,000 years relative to the fixed stars.[5] Apsidal precession occurs in the plane of the ecliptic and alters the orientation of the Earth’s orbit relative to the ecliptic. This happens primarily as a result of interactions with Jupiter and Saturn. Smaller contributions are also made by the sun’s oblateness and by the effects of general relativity that are well known for Mercury.

Apsidal precession combines with the 25,771.5-year cycle of axial precession (see above) to vary the position in the year that the Earth reaches perihelion. Apsidal precession shortens this period to 23,000 years on average (varying between 20,800 and 29,000 years).[5]

As the orientation of Earth’s orbit changes, each season will gradually start earlier in the year. Precession means the Earth’s nonuniform motion (see above) will affect different seasons. Winter, for instance, will be in a different section of the orbit. When the Earth’s apsides (extremes of distance from the sun) are aligned with the equinoxes, the length of spring and summer combined will equal that of autumn and winter. When they are aligned with the solstices, the difference in the length of these seasons will be greatest.

Orbital inclination[edit]

The inclination of Earth’s orbit drifts up and down relative to its present orbit. This three-dimensional movement is known as “precession of the ecliptic” or “planetary precession”. Earth’s current inclination relative to the invariable plane (the plane that represents the angular momentum of the Solar System, approximately the orbital plane of Jupiter) is 1.57°.

Milankovitch did not study planetary precession. It was discovered more recently and measured, relative to Earth’s orbit, to have a period of 70,000 years. However, when measured independently of Earth’s orbit, but relative to the invariable plane, precession has a period of 100,000 years. This period is very similar to the 100,000-year eccentricity period. Both periods closely match the 100,000-year pattern of glacial events.[6]

Theory constraints[edit]

Tabernas Desert, Spain: Cycles can be observed in the colouration and resistance of different strata of sediments.

Materials taken from the Earth have been studied to infer the cycles of past climate. Antarctic ice cores contain trapped air bubbles whose ratios of different oxygen isotopes are a reliable proxy for global temperatures around the the ice was formed. Study of this data concluded that the climatic response documented in the ice cores was driven by northern hemisphere insolation as proposed by the Milankovitch hypothesis.[7]

Analysis of deep-ocean cores and of lake depths,[8][9] and a seminal paper by Hays, Imbrie, and Shackleton[10] provide additional validation through physical evidence. Climate records contained in a 1,700 ft (520 m) core of rock drilled in Arizona show a pattern synchronized with Earth’s eccentricity, and cores drilled in New England match it, going back 215 million years.[11]

100,000-year issue[edit]

Of all the orbital cycles, Milankovitch believed that obliquity had the greatest effect on climate, and that it did so by varying the summer insolation in northern high latitudes. Therefore, he deduced a 41,000-year period for ice ages.[12][13] However, subsequent re[10][14][15] has shown that ice age cycles of the Quaternary glaciation over the last million years have been at a period of 100,000 years, which matches the eccentricity cycle.

Various explanations for this discrepancy have been proposed, including frequency modulation[16] or various feedbacks (from carbon dioxide, cosmic rays, or from ice sheet dynamics). Some models can reproduce the 100,000-year cycles as a result of non-linear interactions between small changes in the Earth’s orbit and internal oscillations of the climate system.[17][18]

Jung-Eun Lee of Brown University proposes that precession changes the amount of energy that Earth absorbs, because the southern hemisphere’s greater ability to grow sea ice reflects more energy away from Earth. Moreover, Lee says, “Precession only matters when eccentricity is large. That’s why we see a stronger 100,000-year pace than a 21,000-year pace.”[19][20]

Some have argued that the length of the climate record is insufficient to establish a istically ificant relationship between climate and eccentricity variations.[21]

Transition changes[edit]

Variations of cycle s, curves determined from ocean sediments

In fact, from 1-3 million years ago, climate cycles did match the 41,000-year cycle in obliquity. After 1 million years ago, the Mid-Pleistocene Transition (MPT) occurred with switch to the 100,000-year cycle matching eccentricity. The transition problem refers to the need to explain what changed 1 million years ago.[22] The MPT can now be reproduced in numerical simulations that include a decreasing trend in carbon dioxide and glacially induced removal of regolith.[23]

Interpretation of unsplit peak variances[edit]

Even the well-d climate records of the last million years do not exactly match the shape of the eccentricity curve. Eccentricity has component cycles of 95,000 and 125,000 years. However, some reers say the records do not show these peaks, but only show a cycle of 100,000 years.[24] However, the split between the two eccentricity components is observed at least ones in a drill core from the 500 million years old Scandiian Alum Shale.[25]

Unsynced stage 5 observation[edit]

Deep-sea core samples show that the interglacial interval known as marine isotope stage 5 began 130,000 years ago. This is 10,000 years before the solar forcing that the Milankovitch hypothesis predicts. (This is also known as the causality problem, because the effect precedes the putative cause.)[26]

Predicted effects mystery[edit]

420,000 years of ice core data from Vostok, Antarctica re ion, with more recent s on the left

Physical evidence shows that the variation in Earth’s climate is much more extreme than the variation in the intensity of solar radiation calculated as the Earth’s orbit evolves. If orbital forcing causes climate change, science needs to explain why the observed effect is amplified out of linear proportion to the theoretical cause.

Some climate systems exhibit amplification (positive feedback) and others exhibit damping responses (negative feedback). As an illustration, if during an ice age the northern land masses were covered in year-round ice, solar energy would be reflected away, counteracting the eventual warming effect from orbital forcing and extending the ice age.

The Earth’s current orbital inclination is 1.57° (see above). Earth presently moves through the invariable plane around January 9 and July 9. At these s, there is an increase in meteors and noctilucent clouds. If this is because there is a disk of dust and debris in the invariable plane, then when the Earth’s orbital inclination is near 0° and it is orbiting through this dust, materials could be accreted into the atmosphere. This process could explain the narrowness of the 100,000-year climate cycle.[27][28]

Present and future conditions[edit]

Past and future of daily average insolation at top of the atmosphere on the day of the summer solstice, at 65° N latitude. The green curve is with eccentricity e hypothetically set to 0. The red curve uses the actual (predicted) value of e. Blue dot is current conditions, at 2000 CE

Since orbital variations are predictable,[29] any model that relates orbital variations to climate can be run forward to predict future climate, with two caveats: the mechanism by which orbital forcing influences climate is not definitive; and non-orbital effects can be important (for example, the human impact on the environment principally increases greenhouse gases resulting in a warmer climate[30][31][32]).

An often-cited 1980 orbital model by Imbrie predicted “the long-term cooling trend that began some 6,000 years ago will continue for the next 23,000 years.”[33] More recent work suggests that orbital variations should gradually increase 65° N summer insolation over the next 25,000 years.[34][failed verification] Earth’s orbit will become less eccentric for the next 100,000 years, so changes in this insolation will be dominated by changes in obliquity, and should not decline enough to permit a new glacial period in the next 50,000 years.[35][36]

Other celestial bodies[edit]

Mars[edit]

Since 1972, speculation sought a relationship between the formation of Mars’ alternating bright and dark layers in the polar layered deposits, and the planet’s orbital climate forcing. In 2002, Laska, Levard, and Mustard showed ice-layer radiance, as a of depth, correlate with the insolation variations in summer at the Martian north pole, similar to palaeoclimate variations on Earth. They also showed Mars’ precession had a period of 51 kyr, obliquity had a period of 120 kyr, and eccentricity had a period ranging between 95 and 99 kyr. In 2003, , Mustard, Kreslavsky, Milliken, and Marchant proposed Mars was in an interglacial period for the past 400 kyr, and in a glacial period between 400 and 2100 kyr, due to Mars’ obliquity exceeding 30°. At this extreme obliquity, insolation is dominated by the regular periodicity of Mars’ obliquity variation.[37][38]Fourier analysis of Mars’ orbital elements, show an obliquity period of 128 kyr, and a precession index period of 73 kyr.[39][40]

Mars has no moon large enough to stabilize its obliquity, which has varied from 10 to 70 degrees. This would explain recent observations of its surface compared to evidence of different conditions in its past, such as the extent of its polar caps.[41][42]

Outer Solar system[edit]

Saturn’s moon Titan has a cycle of approximately 60,000 years that could change the location of the methane lakes.[43][44] Neptune’s moon Triton has a variation similar to Titan’s, which could cause its solid nitrogen deposits to migrate over long scales.[45]

Exoplanets[edit]

Scientists using computer models to study extreme axial tilts have concluded that high obliquity could cause extreme climate variations, and while that would probably not render a planet uninhabitable, it could pose difficulty for land-based life in affected areas. Most such planets would nevertheless allow development of both simple and more complex lifeforms.[46] Although the obliquity they studied is more extreme than Earth ever experiences, there are scenarios 1.5 to 4.5 billion years from now, as the Moon’s stabilizing effect lessens, where obliquity could leave its current range and the poles could eventually point almost directly at the Sun.[47]

References[edit]

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Further reading[edit]

• The oldest reference for Milankovitch cycles is: Milankovitch M (1930). Mathematische Klimalehre und Astronomische Theorie der Klimaschwankungen. Handbuch der Klimatologie. 1 Teil A. von Gebrüder Borntraeger. OCLC 490063906.
• Roe G (2006). “In defense of Milankovitch”. Geophysical Re Letters. 33 (24): L24703. Bibcode:2006GeoRL..3324703R. doi:10.1029/2006GL027817. S2CID 13230658. This shows that Milankovitch theory fits the data extremely well, over the past million years, provided that we consider derivatives.
• Kaufmann RK, Juselius K (2016). “Testing competing forms of the Milankovitch hypothesis”. Paleoceanography. 31 (2): 286-297. Bibcode:2016PalOc..31..286K. doi:10.1002/2014PA002767..
• Edvardsson S, Karlsson KG, Engholm M (2002). “Accurate spin axes and solar system dynamics: Climatic variations for the Earth and Mars”. Astronomy and Astrophysics. 384 (2): 689-701. Bibcode:2002A&A…384..689E. doi:10.1051/0004-6361:20020029. This is the first work that investigated the derivative of the ice volume in relation to insolation (page 698).
• Zachos J, Pagani M, Sloan L, Thomas E, Billups K (April 2001). “Trends, rhythms, and aberrations in global climate 65 Ma to present”. Science. 292 (5517): 686-93. Bibcode:2001Sci…292..686Z. doi:10.1126/science.1059412. PMID 11326091. S2CID 2365991.

  This review article es cycles and great-scale changes in the global climate during the Cenozoic Era.

• Pälike H, Norris RD, Herrle JO, Wilson PA, Coxall HK, Lear CH, et al. (December 2006). “The heartbeat of the Oligocene climate system” (PDF). Science. 314 (5807): 1894-8. Bibcode:2006Sci…314.1894P. doi:10.1126/science.1133822. PMID 17185595. S2CID 32334205. A 13-million-year continuous record of Oligocene climate from the equatorial Pacific reveals a pronounced “heartbeat” in the global carbon cycle and periodicity of glaciations.

External s[edit]

to Milankovitch cycles at Wiki Commons

Milankovitch cycles at Wikibooks

• Ice Age – Milankovitch Cycles – National Geographic Channel
• The Milankovitch band, Internet of American Geophysical Union lecture
• Campisano, C. J. (2012) Milankovitch Cycles, Paleoclimatic Change, and Hominin Evolution. Nature Education Knowledge 4(3):5

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