The Moon’s formation could have happened much earlier than previously believed. New research suggests it may have formed as early as 4.53 billion years ago, hundreds of millions of years before earlier estimates.
An international team led by Francis Nimmo, a geologist at the University of California Santa Cruz, reexamined the Moon’s history. Their analysis suggests the Moon’s formation timeline may be decades earlier than once assumed. This new perspective also helps solve several mysteries about its surface features.
REVISITING THE LEADING THEORY: THE GIANT IMPACT HYPOTHESIS
The leading theory of the Moon’s creation is the giant impact hypothesis. In the early days of the Solar System, Earth was still hot, and a Mars-sized object collided with it. This catastrophic impact sent a massive amount of Earth’s mass into orbit, eventually coalescing into it.
ZIRCON CRYSTALS: A KEY TO THE AGE
The Moon’s age has traditionally been pegged at 4.35 billion years based on the assumption of a global magma ocean formed after its creation. But recent studies of lunar zircon crystals have given scientists new insights. These crystals, formed when the Moon’s surface cooled, have been dated at 4.46 billion to 4.51 billion years old. This is far older than expected and suggests a different formation timeline.
WHAT’S SPECIAL ABOUT ZIRCONS?
Zircon crystals are perfect for dating because they incorporate uranium during their formation but strongly reject lead. Over time, uranium decays into lead at a steady rate, allowing scientists to precisely measure their age. Zircons found on the Moon present an interesting paradox: they’re older than the traditional 4.35 billion-year estimate of the Moon’s surface rock.
SOLVING THE PARADOX: CRUSTAL REMELTING
To resolve the discrepancy between the older zircons and younger rocks, Nimmo and his colleagues proposed a solution. They suggested that the Moon formed earlier, then experienced widespread crustal remelting around 4.35 billion years ago. This could have occurred due to tidal forces caused by the Moon’s eccentric orbit.
ECCENTRIC ORBITS AND TIDAL HEATING
When two celestial bodies orbit each other, their orbits aren’t perfectly circular. Instead, they trace elliptical paths, leading to varying gravitational pulls. This stretching and squishing of bodies create friction, generating heat. In the Moon’s early days, before its orbit stabilized, this eccentricity may have caused enough heat to melt parts of the lunar surface for tens of millions of years.
A REVISED MOON AGE: BETWEEN 4.43 AND 4.53 BILLION YEARS
With this new model, the Moon’s formation can now be estimated between 4.43 and 4.53 billion years ago. Since Earth is believed to have formed around 4.54 billion years ago, this places the creation almost concurrently with the formation of our planet.
SOLVING OTHER MOON MYSTERIES
The earlier formation timeline could also explain several other puzzles about the Moon. Scientists have long been puzzled by the Moon’s lack of large impact basins. This is surprising considering the heavy bombardment that occurred during the early Solar System. Tidal remelting could have erased these impact features, solving the mystery of their scarcity.
Additionally, the Moon’s surface holds far less metal than Earth’s, likely due to a lack of planetesimal collection during formation. If its surface underwent remelting, metals could have sunk below the lunar surface, further explaining this difference.
THE AGE OF THE SOUTH POLE-AITKEN BASIN
The study also places constraints on the age of the South Pole-Aitken Basin. It is one of the largest impact basins on the Moon. If its surface experienced tidal remelting at 4.35 billion years ago, this would suggest the basin formed prior to that event.
THE ULTIMATE MYSTERY: DID ALIENS SCATTER ZIRCONS?
Unless, of course, extraterrestrial beings randomly deposited zircons across the Moon just for fun. In that case, all bets are off. But for now, this new study presents a compelling new understanding of the Moon’s formation. It also clarifies its relationship with Earth’s early history.
