By D. W. G. Kalani Tharanga, JadeTimes News
Lunar Influence on Earth’s Days
Billions of years ago, the Earth experienced shorter days, lasting less than 13 hours. The ongoing extension of the day length is attributed to the dynamic relationship between the Moon and Earth's oceans. The Moon, an ever present entity in human history, orchestrates the tides through its gravitational pull and influences various natural phenomena, such as animal behavior and ancient calendars.
Some theories suggest that the Moon was instrumental in creating conditions conducive to life on Earth and might have even sparked the origin of life. Its irregular orbit affects critical weather systems today. However, the Moon is gradually distancing itself from Earth, a phenomenon known as "lunar recession." This recession has been measured with high precision using lasers reflected off devices left by Apollo astronauts, revealing that the Moon recedes by 1.5 inches (3.8 cm) annually. As the Moon moves away, Earth’s rotation slows, lengthening the day.
David Waltham, a professor of geophysics at Royal Holloway, University of London, explains that this process is driven by tidal drag. The Moon’s gravity creates tidal bulges in Earth's oceans, and the friction between these bulges and Earth’s rotation gradually slows the planet’s spin. Consequently, the Moon gains this energy as angular momentum, pushing it into a higher orbit.
This gradual deceleration has increased the average length of an Earth day by about 1.09 milliseconds per century since the late 1600s. Over Earth's 4.5 billion year history, this accumulation has led to significant changes.
Historical and Future Impacts of Lunar Recession
The prevailing theory is that the Moon formed within the first 50 million years of the Solar System’s existence, following a collision between Earth and a Mars sized object, Theia. Geological evidence indicates that the Moon was once much closer to Earth than it is today. Around 3.2 billion years ago, the Moon was approximately 270,000 km (170,000 miles) away, significantly closer than its current 384,400 km (238,855 miles) distance.
Tom Eulenfeld, a geophysicist at Friedrich Schiller University Jena, notes that the faster rotation of the early Earth resulted in two sunrises and sunsets every 24 hours. This could have moderated temperature variations and influenced the biochemistry of early photosynthetic organisms.
Research shows that the rate of lunar recession has fluctuated over time. For instance, between 550 to 625 million years ago, the Moon might have been retreating at up to 7 cm (2.8 inches) per year. Currently, the rate of recession is unusually high. David Waltham attributes this to the resonance effect created by the size and shape of the Atlantic Ocean, which amplifies the tidal forces.
Future changes in the Earth's geography will continue to influence this process. In about 150 million years, a new tidal resonance is predicted to emerge, only to disappear 100 million years later with the formation of a new supercontinent. Despite the current high rate of retreat, the Moon will likely never completely escape Earth’s gravitational pull, as the Sun’s evolution will intervene first, around 5 to 10 billion years from now.
In the nearer future, human induced climate change might also affect the length of days. Melting glaciers and ice caps, resulting in more free water, could slightly extend day length by altering tidal forces. However, this effect is complex and may be counterbalanced by other factors like rebounding landmasses.
Upcoming lunar missions, such as NASA's Artemis program, may allow astronauts to observe Earth from slightly further away than during the Apollo missions. For most of us, however, the gradual lengthening of days by picoseconds remains imperceptible in our brief lifetimes.