The source data is a 1x1° equirectangular elevation map 360° wide and 180° tall where an elevation of 0 indicates surface level (land). It's pulled from here. I processed data locally, using d3-contour to generate contour polygons at an elevation threshold of 0 for each of the snapshots in the data set (1 snapshot every 5 million years from present-day back to 540Ma). The result is">