Is the Moon Moving Farther Away from Earth?
As the Moon travels around Earth, it affects Earth’s rotation. Scientists have determined that the Moon slowly gets farther away from Earth at the rate of about 1.5 inches per year. This movement causes Earth to rotate more slowly around its axis, similar to the way a figure skater begins to slow down as she stretches her arms out.
Researchers who have studied the interaction between Earth and the Moon believe that approximately 1.4 billion years ago, a day on Earth was just 18 hours long. At current rates of movement, they believe days on Earth are getting longer by about 0.000018 seconds each year.
How did scientists make these calculations? They used a new statistical method called astrochronology, which combines geological observation of very old rocks with astronomical theory to reconstruct the history of Earth and its interactions with the solar system.
When used in concert with radiometric dating, it allows the resolution of timescales to a high degree of accuracy. If orbital precession cycles are identified, the dating error can be as low as 21,000 years.
Sounds complicated? It is! Specifically, scientists were able to study ancient rock formations to track changes in Earth’s orbital variation, known as Milankovitch cycles. These cycles are the result of orbital forcing, which are climate changes caused by changes in Earth’s tilt, wobble, and orbit around the Sun.
Astrochronology has emerged as an important tool for enhancing the accuracy and precision of high-resolution time scales, especially through ash-poor intervals that cannot be directly dated with radioisotopic methods. Astrochronology uses the geologic record of climate oscillations—those ascribed to periodic changes in the Earth’s orbit and rotation—to measure the passage of time from rhythmic layers in strata.
Major advancements in astrochronology derive from improvement of the theoretical astronomical models, the acquisition of high-quality paleoclimate records and their integration with bio-chemo-magneto-litho-stratigraphy and radioisotopic data, and the development of statistical methodologies to assemble and evaluate cyclostratigraphic records. Astrochronology is now even used to calibrate and evaluate radioisotopic geochronology.
Scientists also concluded that the rate at which the Moon is moving away from Earth has changed over time. Since the Moon is about 4.5 billion years old, they concluded that, at the present rate of the Moon’s movement, it would’ve been too close to Earth to avoid being ripped apart long ago. As a result, they believe the Moon’s movement away from Earth was much slower billions of years ago.