Rocks because those 4 planets Mercury, Venus, Earth, and Mars are rocky planets. Also, this is a tip, anytime you are forgetting the order of the planets, use this term:
My
Very
Excellent
Mother
Just
Served
Us
Nachos
It will help you remember the actual order which is
Climate oscillation or climate cycles are a recurring oscillation within the global or regional climates and their fluctuations produce varying climatic cells and pressures often occurring on an interannual and multi annular basis.
On a decadal and millennium timescales.Current examples of the ENSO, Pacific oscillation, Antarctica, and arctic oscillation. like ENSO is characterized by flooding and drought conditions and the distribution of extreme conditions in the form of heat and cold waves.
Other cycles like the Piora oscillation, Little ice age, medieval warm period, retreating of glaciers and warming of the planet. All these cycles move on earth from the equator to tropics to temperate to polar areas and the continuous warming and cooling periods have altered the rate of spreading of the seafloor and oceanic basin.
Present warming has drastically created a major change in the evolution of species causing extinction and quick decomposition of resources. The release of carbon and methane gases over these years have raised the greenhouse effect at alarming rates.
