Complex sentence: Geologists like Suess have found fossils of ocean creatures in rocks in the Himalayas, indicating that those rocks were once underwater, before the Indian continental shelf began pushing upward as it smashed into Cimmeria.
Split into simpler sentences: Geologists like Suess have found fossils of ocean creatures in rocks in the Himalayas. So, we know those rocks were underwater, before the Indian continental shelf began pushing upward as it smashed into Cimmeria.