About 1.3 billion years ago, a year had 546 days and 13 to 14 months, a month had 42 days and a day had almost 16 hours, according to geologists who have spent the past five years studying fossilised bacteria. A team from Tianjin Geology and Mineral Resource Institute inspected the algae to find 'our own ample evidence' to support a 50-year-old theory that certain geological patterns are related to the earth's rotation, said research leader Zhu Shixing. The findings in China and others from space show that the Earth has been slowing down during the 4.6 billion years since the Earth was formed. 'Our evidence of 1.3 billion years ago should be the oldest one to back the theory,' Mr Zhu said. Among 600 stromatolites - fossilised layers of bacteria - in the Yanshan Mountain of Hebei province, the geologists found evidence of blue-green algae, or cyanobacta, thought to be the most ancient organisms in the world. The stromatolites form in light and dark layers. The light strips were algae buried in the daytime, during photosynthesis, and the dark strips were buried in the evening when photosynthesis stopped. 'They look like the annual rings of trees. From these strips we can easily and clearly identify how long days were,' Mr Zhu said. They also related differences in thickness of the layers to tidal forces, which are caused by the moon, and so were able to calculate the length of the month. The geologists believe bands without aglae formed during colder periods, helping to determine the length of seasons and the year.