Unit 6 Newsela 3-10-21

Sometimes the day does not feel long enough. However, that is changing. New calculations have been made. The results tell us that the days are getting longer. The recent calculations indicate a day on Earth was a full five hours and 15 minutes shorter more than a billion or so years ago. This was a very long ago; it was a time before complex life spread around the planet.

Scientists used a combination of tools to find out about Earth's longer days. They used an astronomical theory. It involves using physics and chemistry to describe objects in space.

They also used geochemical signatures buried in ancient rocks. The ancient rocks showed that 1.4 billion years ago a day on Earth was 18 hours and 41 minutes long. A day on Earth is measured when the Earth turns a full revolution on its axis. In other words, it is how long the Earth takes to complete one rotation or full spin. 

In modern times, a day is 23 hours, 56 minutes and 4 seconds. That means the length of days has, on average, grown over time. It has increased by about one 74-thousandths of a second per year in the last 1.4 billion years. That trend is expected to continue. Scientists think it will continue for millions, if not billions, of years more.  

As the Earth's rotation gradually winds down, the moon moves further away. Stephen Meyers is a geoscientist at the University of Wisconsin-Madison. He worked with Alberto Malinverno, a geophysicist at Columbia University in New York. Together they published their findings in a science journal called Proceedings of the National Academy of Sciences. They calculated how far away the moon is from Earth now. Over the past 1.4 billion years the moon has drifted about 44,000 kilometers from Earth. The moon is now a distance of 384,400 kilometers away from Earth. 

Meyers and Malinvern set themselves the task of reconstructing changes in the distance between the Earth and the moon. They studied the Earth's Milankovitch cycles. They are the variations in Earth's orbit, along with its wobbles and tilts toward the sun. They went further back in time than ever before. Until now, it has been hard to work out reliable figures for more than 50 million years ago. 

Milankovitch cycles affect how much sun reaches the planet's poles. That means they are prime drivers of climate change over long periods of times, ranging from tens of thousands of years to millions of years.

To pin down the frequency of the cycles in Earth's deep history, the scientists studied ancient rocks. They examined copper and aluminum ratios linked to climate change in the rocks. They looked at a 1.4-billion-year-old Xiamaling marine sediment in northern China. They compared it to a 55-million-year-old Walvis ridge in the south Atlantic. 

"We were interested in reconstructing the Milankovitch cycles because they provide a powerful tool for evaluating the history of our planet, and the solar system. They are like signposts on a trail, allowing us to navigate geological history," said Meyers. 

Studying the ancient rocks helped the scientists learn more about the Earth. Not only did they learn that the days on Earth are getting longer, they also learned more about Earth's ice ages. "The identification of Milankovitch cycles in sediments spanning the past million years has revolutionized our understanding of the nature of ice ages, the instability of ice sheets and how Earth's climate system works." 

As for the moon, it will not retreat from Earth forever. At some point in the far future, it will reach a stable distance when it will be visible only from one half of Earth, and never seen from the other.