What controls the advance and retreat of these large glaciers during the four long, cool periods?

Scientists understand more about why glaciers advance during cool periods than they do about why large scale cool periods occur, because they have gathered large quantities of data about the current cool period. Variation in the Earth's orbit through time causes changes in the amount and distribution of sunlight (and other solar radiation) reaching the Earth's surface. These changes are thought to affect the development of ice sheets.

Although the idea that variation in the Earth's orbit causes glacial-interglacial cycles originated in the mid 1800s, Milutin Milankovitch first popularized it in about 1920. Although Milankovitch's hypothesis was not widely accepted at first; data collected during the 1970's have generated broad support for it.

Three orbital parameters are especially important in causing ice sheet waxing and waning:

• Changes in the eccentricity of the Earth's orbit
• Changes in the tilt of the Earth's axis
• The precession of the equinoxes

In combination these factors influence the amount and distribution of solar radiation reaching the Earth. Changes vary with both latitude and season. Because of the different periodicities of variation for the three factors, the composite variations in solar radiation are very complex.

Although the connections are not obvious and direct, changes in the amount of solar radiation are thought to drive the growth and melting of major ice sheets. Over the last 750,000 years ice sheets have expanded into the midwestern United States at least 8 major times. The timing of some of these advances is not well known.

The last glaciation of the midwestern United States had its maximum extent approximately 20,000 years ago. The animals and plants discussed in this exhibit are the ones that were living in the midwestern U.S. during and just following that glaciation.

Eccentricity

The Earth's orbit around the sun is not a circle, but rather it is an ellipse. The shape of the elliptical orbit, which is measured by its eccentricity, varies from between one and five percent through time.

The eccentricity affects the difference in the amounts of radiation the Earth's surface receives at aphelion and at perihelion. The effect of the radiation variation is to change the seasonal contrast in the northern and southern hemispheres. For example, when the orbit is highly elliptical, one hemisphere will have hot summers and cold winters; the other hemisphere will have warm summers and cool winters. When the orbit is nearly circular, both hemispheres will have similar seasonal contrasts in temperature.

Although the amount of change in radiation is very small (less than 0.2%), it is apparently extremely important in the expansion and melting of ice sheets.

The eccentricity of the Earth's orbit varies in a periodic manner. The primary periodicity is approximately 100,000 years.

Tilt

The Earth's axis is tilted with respect to its orbit around the sun. Today the tilt is approximately 23.5 degrees. The tilt varies from between 21.6 and 24.5 degrees in a periodic manner. A graph of the tilt over the last 750,000 years shows that the dominant period of this variation is approximately 41,000 years.

Changes in the tilt of the Earth's axis cause large changes in the seasonal distribution of radiation at high latitudes and in the length of the winter dark period at the poles. Changes in tilt have very little effect on low latitudes.

The effects of tilt on the amount of solar radiation reaching the Earth are closely linked to the effects of precession. Variation in these two factors cause radiation changes of up to 15% at high latitude. Radiation variation of this magnitude greatly influences the growth and melting of ice sheets.

Graph of the tilt of the Earth's axis

This graph shows the variation in the tilt of the Earth's axis over the last 750,000 years. The blue line traces the tilt. The orange line shows today's value for comparison.
 

Precession of the equinoxes

Twice a year, the equinoxes, the sun is positioned directly over the equator. Currently the equinoxes occur on approximately March 21 and September 21. However, because the Earth's axis of rotation "wobbles" (like a spinning top), the timing of the equinoxes changes . The change in the timing of the equinoxes is known as precession.

Although the timing of the equinoxes is not in itself important in determining climate, the timing of the Earth's aphelion and perihelion also changes. Like the timing of the equinoxes, the timing of the aphelion and perihelion is also affected by the wobble of the axis of rotation.

The changing aphelion and perihelion is important for climate because it affects the seasonal balance of radiation. For example, when perihelion falls in January the northern hemisphere winter and southern hemisphere summer are slightly warmer than the corresponding seasons in the opposite hemispheres.

The aphelion and perihelion change position on the orbit through a cycle of 360 degrees. The cycle has two periods of approximately 19,000 and 23,000 years. Together these combine to produce a generalized periodicity of about 22,000 years.

The effects of precession on the amount of solar radiation reaching the Earth are closely linked to the effects of tilt. Variation in these two factors cause radiation changes of up to 15% at high latitude. Radiation variation of this magnitude greatly influences the growth and melting of ice sheets.

The Last Ice Age

The last Ice Age started about 70,000 years ago and ended about 10,000 years ago (during the Pleistocene epoch). The Earth was much colder than it is now; snow accumulated on much of the land, glaciers and ice sheets extended over large areas and the sea levels were lower. These phenomena changed the surface of the earth, forming lakes, changing the paths of rivers, eroding land, and depositing sand, gravel, and rocks along the glaciers' paths.

Land at the Poles

Antarctica has been located near the South Pole for about the last 300 million years! Regardless of temperatures, Earth's poles always have been colder than other locations on the globe. And they always have been subject to seasonal fluctuations in light and radiation. When a land mass lies in a polar position it forms an ideal spot to start an ice sheet, if the global temperatures are cool enough to support ice at the pole. What has added to the glaciation of Antarctica is the isolation of the continent from other land masses. The most recent phase of glaciation on Antarctica began about 40 million years ago as the other continents slowly separated from Antarctica. This allowed the Antarctic Circumpolar Current to flow undeflected around Antarctica, isolating it from warmer water masses.

Shift of the plates away from Antarctica (modified from Lawver et al., 1992). During the Cretaceous (110 million years ago). During the Oligocene (30 million years ago). Through time, Antarctica has been left behind at the South Pole and the ocean currents around the Southern Continent have strengthened to keep warmer waters from intruding. This has helped to maintain ice sheets on the continent for the last 40 million years.

Tectonic Events

Tectonic changes can cause changes in atmospheric circulation and oceanic circulation. These changes take place on time scales of millions of years. A tectonic shift is believed to have happened about 3.5 million years ago, when the Isthmus of Panama formed. The Isthmus cut off east-west ocean current circulation. This strengthened the Gulf Stream, which then delivered warmer water to the Northern Hemisphere. This warm water source increased precipitation over the North Pole region, resulting in the initiation of ice sheets in that region.

Change in circulation. Before the formation of the Isthmus of Panama there was an east-west component of circulation, and the Gulf Stream was not as strong. Following formation of the Isthmus the Gulf Stream became stronger and carried warmer water closer to the pole. This caused an increase in precipitation.

Earth's Orbit

The Antarctic Ice Sheet has been in place for the last 40 million years, but it has grown and diminished in size several times since it's initiation. Likewise, the ice sheets of the Northern Hemisphere have grown and dispersed several times in the last 3.5 million years. Reorganization of Earth's surface components and location of the continents can set the stage for ice sheets. But what has caused the fluctuations of ice in the Northern Hemisphere and Antarctica?

Many researchers believe that fluctuations in the volume of ice on Earth are caused by slight changes in the path of Earth around the sun. This causes a redistribution of solar radiation striking Earth's surface. The amount of incoming radiation has not changed. The changes in Earth's path can be broken into three components:

Orbital Eccentricity - the path of Earth around the sun changes from being nearly circular, with the perihelion and aphelion being equal distance, to being more elliptical, with a difference in the perihelion and aphelion. These changes take place on a time scale of about 100,000 years, and probably are cause by the gravitational pull of Earth by other planets.

Inclination - the tilt of Earth's axis changes through time. If the tilt is increased, there is an increase in the duration of winter darkness at the poles. The time scale for changes in tilt is about 41,000 years. Changes in axial tilt are most important at the poles.

Precession of the Equinoxes - as Earth moves around the sun, it's path wobbles slightly because of the pull of the sun and the moon. This means that the poles are tilted toward the sun at different positions in the orbit. The Northern Hemisphere winter has not always occurred at aphelion, when Earth is farthest in its orbit from the sun. At times in the past, the Northern Hemisphere has tilted toward the sun at perihelion.

Changes in Earth's orbit: orbital eccentricity, inclination or tilt, precession of the equinoxes (modified from Dawson, 1991).

These slight changes in Earth's journey around the sun combine to cause changes in the distribution of solar radiation on Earth's surface. During times of the most elliptical path of Earth around the sun, the difference in winter and summer in the Northern Hemisphere are increased and the extremes in the seasons in the Southern Hemisphere are decreased. This could trigger the development of ice sheets close to the North Pole. When tilt of Earth's axis is greatest, there is an increase in the north-south atmospheric circulation, which causes an increase in the delivery of precipitation toward both poles.

The predictable changes in Earth's orbit may act in concert with tectonic changes and the distribution of land over the globe. These shorter-time scale changes in orbit, which cause changes in the distribution of solar radiation across the globe, may help us understand why ice sheets have fluctuated in size in Antarctica during the last 40 million years, and why ice sheets have grown and decayed so many times in the Northern Hemisphere in the last 3.5 million years!

Why were there four long, generally cool periods during which continent-sized glaciers advanced and retreated?

Although scientists cannot answer this question with certainty, they know that a number of factors interact to produce conditions favoring the formation of ice sheets. Some of these factors include changing continental positions uplift of continental blocks reduction of CO2 in the atmosphere

Changes in the Earth's orbit

Long ice age intervals did not just suddenly occur. Instead, they seem to have been the culmination of even longer periods of worldwide climatic cooling. This cooling took place for tens of millions of years before the beginning of glaciation.

Once ice sheets start to grow, they probably contribute to their own further development. This positive feedback occurs because ice sheets reflect more sunlight back into space than does ground not covered by ice. The reflected sunlight would otherwise warm the Earth's surface. Consequently, the presence of ice sheets may lead to more cooling and continued development of ice sheets.
 

Changing Continental Positions

Plate tectonics is an important process influencing when ice ages occur, and the position of the continents is probably one of the most important factors controlling long periods of multiple glaciations. The presence of large land masses at high latitude appears to be a prerequisite for the development of extensive ice sheets,because the large accumulations of ice associated with ice sheets cannot form over the ocean.

During the current ice age, which began slightly less than 3 million years ago, several large land masses have been at high latitude. These include Antarctica, much of North America and much of Eurasia. This continental configuration led to extensive glaciation of both North America and Eurasia.

During the ice age that occurred in the Pennsylvanian and Permian, the southern portion of the supercontinent Pangea was at the south pole. The result was extensive glaciation of what is now Africa, South America, India, Antarctica, Australia, and the Arabian peninsula.

The position of the continents during the Late Proterozoic glaciation (around 700 million years ago) is not well-known. Evidence of glaciers exists from North America, Australia, and Africa.

Uplift of continental blocks

Plate tectonics probably contributes to the development of long periods with many glaciations in a second, more subtle way. Plate movements sometimes cause uplift of large continental blocks. Major uplift can cause profound changes in the global oceanic and atmospheric circulation patterns. Changing circulation patterns cause climate change. Some scientists hypthesize that climatic changes cause by uplift are critical to the development of ice ages.

Over the past 15 million years, the continents have risen about 600 meters (2000 feet) on average. The uplift of the Himalayas and the Tibetian Plateau probably contributed to the initiation of the current cool period.

Similar tectonic uplift appears to have been involved in the three other long, ice age intervals.

Reduction of CO2 in the atmsophere

A general reduction in amount of CO2 in the atmosphere may contribute to the development of ice ages. Carbon dioxide is an important greenhouse gas. Decreases in the amount of CO2 in the atmosphere may lead to global cooling.

Many processes can cause a long-term decrease in the amount of CO2 in the atmosphere. These processes include many complex interactions among organisms, ocean currents, erosion, and volcanism. Important relationships exist between ice ages and the composition of the atmosphere; however, many scientists are unsure whether the changes in atmosphere cause cool periods or whether cool periods cause atmospheric changes. Also, many scientists are not sure the magnitude of past CO2 changes was large enough to initiate ice ages.
 

Changes in the Earth's orbit

The Earth's orbit varies through time. Important parameters that vary include the eccentricity of the orbit around the sun, the tilt of the Earth's axis, and the direction the north pole points. Variation in these three factors changes the amount and distribution of incoming solar radiation. Variations in the distribution of solar radiation affects and initiates glaciations.

However, the variation of the orbital parameters seems to be on too short a time scale to explain the timing of the long, cool intervals with many glaciations. Variations in orbital factors are probably more important in controlling the advance and retreat of large glaciers during the four long, cool periods than they are for controlling the larger-scale patterns.

1) What causes the long-term changes leading to an ice age?

Factors that are thought to play important roles in long-term changes in Earth's climate over millions or tens of millions of years are

Changes in the positions of the continents

Variations in the energy output of the sun

Changes in atmospheric carbon dioxide concentration

Changes in volcanic activity

Influence of the biosphere

2) What causes the glacial cycles within an ice age?

During an ice age, the shorter-term cycles of advancing and retreating glaciers are thought to be driven by regular, predictable variations in Earth's orbit and orientation relative to the Sun.

How do we know that ice ages occurred?

The idea that an ice age had occurred in the past was first proposed by Louis Agassiz in the early 1800s. Agassiz noted that the slow action of mountain glaciers in Switzerland produced certain kinds of features in the surrounding landscape. These include glacial till and erratics, rock striations and loess. He also noted that these features sometimes occurred in areas far from the mountains, where no glaciers existed. Based on these observations, Agassiz came up with the idea that extensive glaciers had existed in the past.

Scientific progress since the time of Agassiz has not only confirmed his idea, but has also begun to reveal a much more detailed picture of what conditions were like during the last ice age. To obtain a more detailed picture of the last ice age, scientists study natural recorders of climate change, such as fossil pollen, ancient coral reefs, ocean sediments and ice cores.

If a planetary body was to come into contact with the

orbital motion of earth or Mobius

Ice ages happen for various reasons two being the orbit and tilt of the planet. But the question is if we came into contact with another planet would that bring about an ice age. This reason why I asked this is the planet Nibiru comes into orbits very close to ours and Mobius's orbit patten ever 3600 years. But because of our colission with Orpheus millions of years ago and the spilting of the two planets and the reforming of both earth and the new planetary body mobius our sister planet and the newly formed moon our orbit in slightly of from what in was in the days when Orpheus was our planetary neighbour how the big question is if Nibiru was to pass the earth or mobius, would the pull of the planetary body be enough to tilt the earths or mobius Axis the answer to this would be yes the drag would tilt the planetary body to what degree is not known at this time but a tilt of that magitude would through the planetary body into a cataclysmic event that would because the next ice age on earth or mobis.

 

The image below show the possible affect of Nibiru passing

closely by the Earth

The same would apply for Mobius if it was to be near Nibiru when it entered into our orbitational flow other times in the cycle of Nibiru orbit around the sun neather planet would be near Nibiru as it passed through the inner planets as it made it way around the sun. The only question left is where is earth and mobius in there orbitational cycles in relation to nibiru orbitational cycle ?