Complex sentence: In the reconstruction of, Arctica formed as a continent during the Tonian 950 Ma as part of Rodinia, and then reformed during the Permian-Triassic 255 Ma as part of Pangaea.
Split into simpler sentences: In the reconstruction of, Arctica originally formed as a continent during the Tonian 950 Ma and became part of the supercontinent Rodinia. It reformed during the Permian-Triassic 255 Ma and became part of Pangaea.