The Moon is older than previously believed
phys.org
phys.org
Just a few weeks ago there was a paper proposing a 4.336 +/- 0.031 Ga age for the Lunar Magma Ocean [1], which is often equated with (esp. in public press [e.g., 2], though not really the same as) the age of the Moon. For comparison, the "40 to 60 Ma after solar system formation" in the new paper [3] discussed here translates into roughly 4.517 +/- 0.010 Ga.
This new paper agrees almost perfectly with one I was a coauthor on a couple years ago though [4], which also gave an age of 4.51 (+/- 0.01) Ga, so maybe we're starting to get slightly closer to some consensus.
[1] https://doi.org/10.1016/j.epsl.2019.07.008
[2] https://www.newscientist.com/article/mg21128265-100-moon-may...
Presumably a system slowly forms out of gas and dust but at what point does the accumulating material cross some threshold to where it is considered a new system? Solar ignition?
https://doi.org/10.1038/ngeo941
"The age of the Solar System can be defined as the time of formation of the first solid grains in the nebular disc surrounding the proto-Sun. This age is estimated by dating calcium–aluminium-rich inclusions in meteorites. These inclusions are considered as the earliest formed solids in the solar nebula. Their formation marks the beginning for several long- and short-lived radiogenic clocks that are used to precisely define the timescales of Solar System events, such as the formation and evolution of planetary bodies1,2,3. Here we present the 207Pb–206Pb isotope systematics in a calcium–aluminium-rich inclusion from the Northwest Africa 2364 CV3-group chondritic meteorite, which indicate that the inclusion formed 4,568.2 million years ago."
True enough, I suppose: ~50 million years vs ~150 million years after solar system formation. But on the scale of ~4.5 billion years ago, that's not such a huge difference. And conversely, 50-100 million years is a long time in the context of stuff with solar orbits on the scale of 1-100 years.
I'm guessing that formation of the Sun and solar system was a strongly exponential process. And the Moon probably formed during the final flurry of adjustments among major bodies.
So was it likely that it was this Jupiter incursion that sent the "Mars-size planet" to the Earth, creating the Moon?
Also, I read somewhere, a few years ago, that the core of said "Mars-size planet" survived the collision, and ended up as Mercury. As I recall, part of the argument was that by composition, Mercury looks like a core, not a planet (not even a near-solar planet). And there perhaps was some isotopic evidence. Maybe also some compositional mass-balance argument like "'proto Earth' + 'Mars-size planet' <> Earth + Moon". There being missing iron etc.
There's a lot of variance in "Mars-sized", so I wouldn't count on an easily noticeable mass-balance match. Mars, Mercury, and the Moon are all very small compared to Earth. Earth is more massive than all of the other rocky planets and the Moon combined, and yes, that includes Venus.