Put your definition on the table in the front of the room. This tilt is the angle between the earth's rotational axis and its orbital plane around the sun. Currently this angle is 23.5 degrees. Long term climate is also affected by the heat balance of the earth which is driven mostly by the concentration of CO 2 in the atmosphere. There is abundant evidence that the earth does undergo climatic change.
Climatic change can be a limiting factor for the evolution of many species.
Eccentricity variation 90,000 years 5 variation around mean value. This is due to Jupiter. Clearly are the result in reducing the amount of sunlight that reaches the surface. But we don't know the causal connection between the impact and the extinction cycle but clearly something basically put a halt to photosynthesis for some period of time. There might also be a component of acid rain from this event that could have harmed much of the plant life that large plant-eaters fed on.