Complex sentence: NY Ideas in the 1970s were erosion by water or thermokarst activity, which is the melting of permafrost in glacial climes.Scientists agree that there was liquid water flowing on the Martian surface in the past.
Split into simpler sentences: NY Ideas in the 1970s were erosion by water or thermokarst activity, which is the melting of permafrost in glacial climes. However, scientists agree that there was liquid water flowing on the Martian surface in the past.