摘要:天长（一天时长）是地球自转速度的直接反映。古生代—中生代化石记录的天长数据表明，古生代—中生代期间的天长随时间呈线性增加。根据角动量守恒定律，这意味着同时段地球自转速度呈线性衰减。如果把这个趋势应用于地球历史的全过程，计算结果为4.519～4.495 Ga，与目前公认的地球绝对年龄4.54 Ga一致。这意味着，从这个时间点起，地球有一种自转速度衰减的总趋势。地球自转速度衰减年龄等值于地球年龄说明：1）所测量的陨石样本生成的时间（表征地球年龄）与地球受月球吸引形成自转减速的时间几乎相同。这意味着地—月体系形成之前的地球比该陨石表征的地球年龄更为古老。2）地球、月球、自转速度衰减时长，三者的年龄呈现等值状态，因而此结果与月球起源于大碰撞的假说可以匹配。
关键词: 化石天长/
角动量守恒/
地球自转速度/
衰减/
地球年龄
Abstract:A new method to calculate the Earth's age with the time length of a day based on fossil growth lines was proposed.The day time length is a direct reflection of the Earth's rotation. The existing Mesozoic-Paleozoic fossil-daily time length data show that the day time length of this period would increase proportionally with time. According to the law of conservation of angular momentum，it is suggested that the rotation velocity of the Earth would attenuated in the same period. If this increasing trend is suitable to the whole history of the Earth，fossil-day time length data can be used to calculate the age of the Earth. The calculations show that the ages obtained vary in a range of 4.519～4.495 Ga，highly consistent with the generally accepted Earth's age of 4.54 Ga. This implies that there has been a total attenuation trend of the Earth's rotation velocity from the formation of the Earth on. The currently recognized absolute age of the Earth is substantially the age of that time point for the Earth rotation velocity to begin attenuation. From this time point forward there has been a total attenuation trend of the Earth's rotation velocity. And its result revealed the essence of currently recognized absolute age of the Earth. The age of the Earth's rotational speed decay is just the time length of the tide exists. So this paper's result of te trinity is favorable to the giant impact theory for the origin of the Moon. This age of the Earth is the last age of reformed earth（new radius，new mass，new spherical surface）.
Key words:Fossil-day time length/
Conservation of angular momentum/
Earth's rotation velocity/
Attenuation Earth's age/
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