Paleontological evidence on the Earth's rotational history suggests that ~1.8 billion years ago, there were about 450 days in a year, implying 20 hour days. Further back, the Earth day had about 17 hours, and there were 514±33 days per year. The Earth–Moon distance for the earliest Palaeoproterozoic was 51.9±3.3 Earth radii (compared to 60.27 at present).