Complex sentence: Kaigas is the first major glaciation period in the Cryogenian period of the Precambrian period, It is almost the entire earth is covered with ice and ice sheets can go up to more than a kilometer thick.
Split into simpler sentences: Kaigas is the first major glaciation period in the Cryogenian period of the Precambrian period. It covered almost the entire earth with ice sheets up to more than a kilometer thick.