Moon’s age: A 4.46 billion lunar puzzle has just been solved

Moon’s age: A 4.46 billion lunar puzzle has just been solved

Moon’s age: A 4.46 billion lunar puzzle has just been solved

Have you ever looked up at the glistening moon amidst the dark satin sky at night and wondered, “How and when did it get there?” How different would life on Earth be without it?

A team of researchers has made a significant leap in unraveling the age-old enigma of the moon’s origins. 

Over 4 billion years ago, in the early days of our solar system, a celestial impact involving a Mars-sized object crashed into our planet, giving birth to our Moon. Using lunar samples brought back to the Earth by Apollo astronauts in 1972, the team has discovered the moon’s presence in our cosmos to be a staggering 4.46 billion years old!

“These crystals are the oldest known solids that formed after the giant impact. And because we know how old these crystals are, they serve as an anchor for the lunar chronology,” said Philipp Heck, the Field Museum’s Robert A Pritzker Curator for Meteoritics and Polar Studies, and the senior author of the newly published study, in a statement.

How did it all come to be?

The genesis of this discovery can be traced back to a collaborative effort led by Jennika Greer, the study’s lead author, who along with Heck and other colleagues, including co-authors Bidong Zhang and Audrey Bouvier, sought a nanoscale perspective of the lunar samples to unlock their secrets.

The lunar dust samples used in this study collected during the Apollo 17 mission contain tiny crystals that formed billions of years ago. Within these lunar fragments lay the key to understanding the Moon’s age. 

The energy of the impact from the Mars-size object hitting the Earth subjected the rock’s surface to a high degree of heat, causing the rocks to melt. “When the surface was molten like that, zircon crystals couldn’t form and survive,” Heck explained.

“So any crystals on the moon’s surface must have formed after this lunar magma ocean cooled.” Since these crystals formed after this impact, their age would reveal the minimum possible age of the Moon.

Moon’s age: A 4.46 billion lunar puzzle has just been solved

A glimpse into the lunar past.

This study marked the first use of a novel analytical method, atom probe tomography. “We start by sharpening a piece of the lunar sample into a very sharp tip, using a focused ion beam microscope, almost like a very fancy pencil sharpener,” said Jennika Greer, elaborating on the process. 

“Then, we use UV lasers to evaporate atoms from the surface of that tip. The atoms travel through a mass spectrometer, and how fast they move tells us how heavy they are, which in turn tells us what they’re made of.”

This meticulous, atom-by-atom analysis, conducted at Northwestern University, revealed how atoms within the zircon crystals had undergone radioactive decay. This decay process converts unstable elements, such as uranium, into more stable elements, like lead. By studying the proportions of these isotopes in the samples, scientists can ascertain their age.

Heck aptly likens this radiometric dating process to an hourglass, where the accumulation of sand in the lower bulb signifies the passage of time. Similarly, radiometric dating relies on measuring the transformation of parent atoms into daughter atoms, allowing researchers to determine the sample’s age.

The proportions of lead isotopes measured led to the astonishing conclusion that the lunar sample is approximately 4.46 billion years old, establishing the Moon’s minimum age.

“It’s amazing being able to have proof that the rock you’re holding is the oldest bit of the Moon we’ve found so far. It’s an anchor point for so many questions about the Earth. When you know how old something is, you can better understand what has happened to it in its history,” said Greer.

Without the Moon, life on Earth would undoubtedly be vastly different. Our days would be of a different length, our tides would ebb and flow differently. Our story is intertwined with the Moon’s.

Source: Interesting Engineering

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Moon’s age: A 4.46 billion lunar puzzle has just been solved

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