4.6 billion years ago each Earth Day was roughly 6 hours long.
Since then, the earth has undergone several changes that gradually slowed it down to our familiar 24 hour day. Felix W. Landerer, a Scientist at NASA's Jet Propulsion Laboratory in California says, “Events like earthquakes, tsunamis, and shifts in tectonic plates led to a change in the distribution of mass on the earth—and hence—its speed.”
At NASA, Landerer and team have been tracking Earth's water movement and surface mass changes, working on a project called GRACE (Gravity Recovery and Climate Experiment). Using scientific tools and satellites, the team monitors changes in ice sheets and glaciers, near-surface and underground water storage, rivers, and changes in sea level and ocean currents.
GRACE provides insight into how Earth's water cycle and energy balance are evolving. It also highlights an unexpected effect of global warming on the movement of our wobbling earth.
For a long time, scientists have been trying to understand how a theory called Milankovitch cycle connects climate change with planetary spin. According to the theory, a change in climate can change the speed of Earth's spin, angle of tilt, and even its orbit. And while climate can change the movement of the Earth, the opposite is also possible.
Historically, changes in Earth's spin, angle, and tilt have been caused by natural processes and were even responsible for the ice ages. As Landerer explains to Supercluster, “the Earth’s axis has never been static—it is constantly changing, wobbling & drifting, due to astronomical effects, as well as due to processes taking place on and within Earth.”
In general, the distribution and re-distribution of Earth’s mass on and beneath the surface—like changes in ice cover, sea level, oceans and, mantle flow—all affect the movement of the planet. However, with the glaciers melting and the sea level rising, unnatural changes in Earth's spin could be a reality, reported NASA. As temperatures have increased substantially throughout the 20th century, the melting of ice at an unprecedented rate has been reported.
There are serious implications for the movement of the blue planet.
If Earth’s ice melts and water stays near the same region, trapped in lakes or below ground, then there is no difference in Earth’s net movement of mass. However, if the water moves down to oceans, equations change. In fact, reports by NASA mention, “a total of about 7,500 gigatons—the weight of more than 20 million Empire State Buildings—of Greenland's ice melted into the ocean” during the 20th century. Such events lead to the transfer of Earth’s mass from polar ice to oceans, leading to sea-level rise and eventually contributing to a drift in Earth’s axis.
These changes are determined by the laws of physics. In a similar manner to how the speed of a moving ice skater changes with the position of their body, the redistribution of Earth's mass would change its spin.
“The shifting mass from melting ice affects the duration of our days. The general tendency is that the length of the day will increase as the ice melts at high latitudes and gets redistributed around the globe” explains Landerer. “The length of each day constantly varies by up to a few milliseconds due to several effects, like that of tides, storms, earthquakes, and so on,” he added.
Since Earth is not a perfect sphere, its rotation on its imaginary axis makes it drift and wobble. Scientists call these spin-axis movements "polar motion." NASA has recorded, since the 20th century, a spin axis drift of about 4 inches (10 centimeters) per year. Calculating this movement over the course of a century, the spin axis drift becomes more than 11 yards (10 meters.)
Moreover, as the Earth is slowing down, scientists have been adding leap seconds since 1988 to atomic clocks to compensate for Earth’s changing speed as it completes one rotation around its axis.
But the question is how does Earth’s changing movement impact us? Landerer tells Supercluster “The day-length changes and variations are very small and imperceptible to us, and the Earth axis movements (aka polar motion) are too small to affect our daily lives.”
Landerer added “the processes that cause polar motion certainly have the potential to be disruptive. This can impact navigation systems, In particular interplanetary travel—like traveling to Mars. Hence, measuring the magnitude of and understanding the processes behind these length-of-day changes is important and has relevant impacts.”
Monika is an independent journalist and writes about the environment, climate change and, sustainability.