How old is the Moon?
This is not a simple question. Here's why...
Once thought to have been created 4.56 billion years ago when a mysterious planet slammed into Earth, a new study says it is actually 4.47 billion years old, 60 million years younger than previous estimates.
This study was conducted by scientists at the Carnegie Institution for Science in Washington, D.C.
What's confusing is last year, the same institute declared it was actually between 4.4 billion and 4.45 billion years old.
So it turns out it's older than previously thought, right?
Anyway, it's still really, really old and a new computer modelling technique that examined 259 simulations of how the solar system evolved.
These form a 'geological clock' to pinpoint the last time something impacted with Earth with enough force to form the Moon.
Astronomer John Chambers, with the Carnegie Institution for Science in Washington DC, said: "We think that the thing that hit Earth and ended up forming the moon, the lion's share of it stayed on Earth.
"A small fraction of its mass and some material from Earth was pushed off into space to form the moon.
"That was probably the last big event."
Previous techniques had relied on measuring the radioactive decay but this had given mixed results.
The moon is thought to have harboured a global ocean of molten rock shortly after its dramatic formation. Currently, the most precisely determined age for the lunar rocks that arose from that ocean is 4.360 billion years, the researchers said.
And here on Earth, scientists have found signs in several locations of a major melting event that occurred around 4.45 billion years ago. So, evidence is building that the catastrophic collision that formed the moon and reshaped Earth occurred around that time, rather than 100 million years or so before, the researchers said.