Scientists have pointed to a prehistoric shoreline along the eastern edge of North America as evidence that much of Antarctica melted 3 million years ago. But new research suggests this shoreline is actually about 30 feet (10 meters) lower than previously thought, meaning less ice melted than suspected. Earth's Mantle Morphs East Coast's Ancient Shorelines oak.ctx.ly Earth's mantle distorted a prehistoric shoreline on the East Coast, affecting sea level rise estimates.The finding shows that scientists have to be careful when looking at Earth for evidence of past sea level changes from the planet's cycles of glacial advance and retreat.