There is a very popular symbolism in Hinduism regarding the degradation of Dharma in the four yugas based on the four legs of a cow. At the beginning the Satya Yuga, the cow had four legs but by the end of the Satya Yuga the cow had only three legs.
By the end of the Treta Yuga, the cow lost another leg.
By the end of the Dwapara Yuga, the cow lost another leg.
By the end of the Kali Yuga, the cow will lose its last leg and there will be Pralaya or the great deluge that will annihilate all Adharma. It will prepare ground for next creation.
The cow losing leg symbolically shows decadence of Dharma. In Satya Yuga there is only Dharma, no one steals, there is no anger, no dishonesty, and not frustration. Everyone is content with what they have. But by the end of Satya Yuga there is change in the attitude of people.
This attitude goes down the line and now we are in Kaliyuga when Dharma is negligible. Adharma flourishes today.
Thus cow who is considered mother earth will lose its last leg and with her fall there will be pralaya. Adharma will be wiped out and fresh ground will be prepared for next cycle of creation.