Hi again, Swordmaker!
In previous message I have explained my hypothesis.
But I have to answer to your questions too.
1) I don’t know exactly what was a cause to change Earth’s orbit. But it could be most possible cause for relative gravitational changes, accordingly to my theory, which defines such changes. And the climatic difference in the past and tomorrow is a fact, especially for the polar areas of the Earth. Other changes simultaneous with Earth’s orbit change, defined in my article, are “just possible”.
2) Elliptical orbit was caused by increasing Earth’s orbital speed in case if there are was impact with e.g. asteroid. Also, elliptical orbit have good correlation with some facts in paleontology (eggs of last dinosaurs have regular structure caused by regular climatic changes).
3) The solar system as gravitational one is very stable. Therefore, it is very possible that elliptical orbit can easily reach the stable circular one.
4) The “sweet” range for the Earth with its oceans is very wide. Nearer to the Sun warmed oceanic water of the Earth increases steam in the athmosphere, which is the best defense against radiation. More, the “greenhouse effect” makes the climatic conditions on the Earth very stable, without large deviations between equator and poles.
Such conditions were on the Earth in the past.
After increasing the distance between Sun and Earth, steam cover was broken, and it was condensed by massive floods and rains which are known facts in the paleontology.
Correction:
“climatic difference in the past and TODAY”