The researchers studied how the coastline of Rio Acu in Brazil changed over time due to rising sea levels. They used seismic data to look at layers of sediment and found evidence of a wide valley that formed during a period of low sea levels. They also discovered ancient river channels and sediment structures that suggest the river used to meander in the area. The researchers identified a tilted block of solid material that affected the distribution of sediments in the region, indicating ongoing geological changes since the last ice age.