You might ask, "So what?" Who really cares if earth's orbit changes? I believe their are important implications to these changes. I believe, at the minimum, these changes in the earth's orbit cause the Ice Ages.
Imagine a washing machine -- the common top-loading design. During the washing machine's spin cycle, if everything is operating according to the way it is supposed to, the drum of the washing machine will be spinning smoothly in a circular "orbit." But sometimes, the load can become unbalanced and the drum starts to spin more elliptically. Of course, this is not what you want your washing machine to do, but imagine the forces involved. In the same way, as the earth's orbital spin becomes more elliptical, the swings in the magnitudes of the forces also become greater! The earth travels faster as it moves closer to the sun, and the slower as it moves further away from the sun. If such swings in magnitude became severe, I believe there would be dramatic implications here on earth. (See also, Gravitational Induction of an Electromagnetic Wave on a Ball-of-Light, Induction off of the sun's core)
I believe this 100,000 year cycle that the earth is going through is not severe enough at this time to cause dramatic changes -- such as inducing a planetary nebula -- but I do believe they are causing the Ice Ages.
Again, what causes the earth's orbit to vary from fairly circular to more elliptical every 100,000 years? I believe the root cause is variations in gravity. I believe, just as there are long term major changes in the solar system's gravitational field caused by changes in direction over the 200,000,000 galactic orbit, there are short term minor changes in the solar system's gravitational field, caused by other changes in direction over a 100,000 year period.
In the section on The Changing Polarity of Earth's Magnetic Field, there was a discussion of how the earth "bobs up and down" as it circles the galaxy. I believe this is the root cause of the flipping of the earth's magnetic polarity. However, the solar system could also be rotating about a common center with another star, or group of stars.
Graphic of earth spinning with other stars within its orbit.
Such a rotation could cause a cycle where gravity is induced -- a cycle where gravitational forces go up and down. As the gravitational force between earth and the sun increases, it accentuates the earth's slightly elliptical orbit. Each year, as the gravitational attraction increases, earth's orbit becomes more elliptical, more dramatic. But then, as the gravitational force wanes, the earth's orbit relaxes back into a more circular ellipse. In other words, this cycle doesn't just happen, the Ball-of-Light Particle Model predicts varying gravity causes it. (See also, Mass Extinctions)
If this secondary orbit is happening every 100,000 years, then our solar system would have:
(Of course, this short-term cycle would periodically combine with the long-term 200,000,000 year cycle that the galaxy has, and the theoretical, medium-term, million year cycle that accounts for the polarity flips in earth's magnetic field.)
What is the importance of having high gravitational fields every 100,000 years? When gravity is high, not only would the earth's orbit be more elliptical, in general -- see exception -- the sun would be more stable. A more stable sun would give off less radiation. Life here on earth would be colder.
Furthermore, a more elliptical orbit would make the variations in temperature from summer to winter greater, thus allowing polar ice to build up quicker.
Elsewhere, I gave an example that stated a massive planet orbiting a star with a highly elliptical orbit could destabilize the star. Actually, it would. However, does the earth have enough mass to destabilize the sun when its orbit becomes more elliptical? I really don't know. However, my guess is, even when the earth's orbit has been at its most elliptical stages, its orbit was not very elliptical from the sun's point of view. It is more likely that the planets: Jupiter, Saturn, Uranus and Neptune would have the most destabilizing affect on the sun's core -- especially Jupiter. Furthermore, with 9 planets, with varying orbital speeds, the averaging of the planet's masses would tend to even out the destabilizing affects on the sun. However, if they all became aligned, then watch out! Their combined gravitational fields would likely seriously destabilize the sun and cause massive solar eruptions that could exterminate life here on earth.
It might be argued by some scientists that as the earth's orbit becomes more elliptical it would receive more energy because it would come closer to the sun. First of all, remember Kepler's third law. On the average, with a more elliptical orbit, the earth would spend less time closer in and more time when further away from the sun. The amount of time it has to soak up the energy is more important than the rate it soaks up in this case. Second, and most importantly, with a higher gravitational field, the sun would be more stable and emit less energy.
There is observational evidence that would seem to indicate that the cause of the ice-ages was a result of the sun emitting less energy -- because the sun was more stable. During a period from about 1645 to 1715 -- known as the "Maunder minimum" -- the sun produced very few sunspots. In other words, it went through a period of high stability, producing less radiation. This lack of sunspots coincided with a period here on earth of unusually cold temperatures -- known as the "Little Ice Age."
To summarize: the Galaxy rotates through 200,000,000 year cycle; one side of the Galaxy is moving away from the center of the Big Bang; one side of the Galaxy is moving towards the center of the Big Bang; the Galaxy has one side moving faster than another side; the side that is moving faster experiences greater gravitational forces; the side moving slower experiences less gravitational forces; this cycle probably causes mass extinctions; as the earth orbits the galaxy it bobs up and down, changing direction within only about a 10,000 year period, but having millions of years when it is either going up or down: these changes in direction appear to coincide with flips in the earth's magnetic polarity; within its local region of the Galaxy it would appear the sun also has another rotational variation -- it is likely rotating around a common center with another star or a small group of stars that causes a 100,000 year cycle that causes the ice ages; in the 100,000 year cycle, the earth's orbit becomes more and less elliptical causing more and less dramatic changes in the seasons; the sun goes through periods of greater or less stability that are caused by cycles of higher or lower gravitational forces; when the sun is more stable it produces less sun spots; when it is more stable it emits less energy; when the sun emits less energy and earth's orbit becomes more elliptical, then earth goes through an ice age.