How many days were there in one year one billion years ago, and how many hours in one day? For the questions above, three Chinese held that there were over 500 days in one year and only 17 hours in one day. Their finding has been published recently on Chinese Science Bulletin, China's authoritative periodical on natural sciences.

Two years ago, under the direction of Professor Gong Yiming, Qu Yuangao and Xie Guwei, then undergraduates at China University of Geosciences conducted investigation on the "stomatolile" at Zhoukoudian, Beijing.

The stomatolile there, affected by factors such as the periodic changes of day and night light intensity and in different seasons, formed bright and dark laminas different in thickness, recording the daily, monthly and seasonal changes of the earth in remote times.

After research on many subjects, the three determined at last that one billion years ago, one year was composed of 496 to 536 days in 12.4 to 13.4 months, 40 days in each month.

Expert says, stomatolile is a kind of biological sedimentary structure the mainly content which is blue-green algae. Algae, which easily bends towards light, is able to record the day and night changes.

The research suggests that we are having longer and longer days. Statistics released by the International Society for Astrological Research (ISAR) show the earth is really moving more and more slowly and days are turning longer. There are astrologists holding that during the early days of the earth (about four to five billion years ago), it took the earth only six hours to complete one rotation, which is the length of one day.

Opinions differ on the reasons for the slower rotation of the earth. One speculation is that it was the lunar tides-caused gravity that depleted the kinetic energy of the earth for rotation. Another is that the rising temperature due to the gradual warming on the earth caused the air to expand, slowing the earth's rotation.