A year has 540 days

Chinese geologists believe that 1.3 billion years ago, one year of the Earth lasted 540 days, ie 13 to 14 months with 42 days a month and only 15 hours a day.

These impressive figures are the result of a long-term study of fossils of ancient green algae. Green algae is one of the oldest life forms on our planet. They are the most primitive and persistent creatures of the unremarked cell group.

Green algae reacts strongly to day and night changes. Under the sun, they grow upright and become bright. When not getting enough light, they spread and are faded. Therefore, understanding this algae's past can help to extrapolate the change in day and night lengths in the period in which they live.

The team studied 1.3 billion years of fossils at the foot of Yanshan Mountain in northern Tianjin, China. They show an accurate picture of the growth of green algae . The rhythm indicates that the Earth's rotation speed was 1.3 billion years ago, far from today .

Before the 20th century, scientists also believed that the speed of rotation of the earth did not change much over time. However, after further analysis of the sun, moon and nebulae, it was clear that the speed of rotation of the earth was slowing down due to the influence of the tide. Over the past 2,500 years, an average astronomical day has extended 0.0024 seconds after every century.

In addition, the rotation speed of the earth is subject to seasonal changes caused by meteorological phenomena and the gravitational pull of the moon. Besides, the researchers also recorded intermittent changes in the speed of the Earth's rotation (resulting in an increase or decrease in the length of a few milliseconds in 1-3 years), but worth especially in 1864, 1876, 1898 and 1920.

Thuan An