Dr. Stone trivia ch56:

Senku's gonna retell the tale of the pirate with a hat of straw, and Chrome'll blurt out, "The One Piece is friendship, right???"

2/ Skarn is a word of Swedish origin that referred to waste rock found in limestone deposits.
Modern usage is more nuanced, as the hodge-podge of metamorphic rocks can be a source of valuable earth metals.

3/ The siphon's water source from the last chapter is huge (a river? or a whole underground lake?), which means it's easy to assume that the water level didn't drop, eliminating one possible unaccounted-for factor from the calculations.

4/ Even Magma's pea brain appreciates a good play on words, based on his own name.

5/ Chalcopyrite (known as fool's gold) and sphalerite are big sources of copper and zinc, respectively. Copper means more wire, and zinc can be used for batteries, just like manganese.

6/ These lines are poignant. Like Senku's just been waiting for the other shoe to drop, hoping they wouldn't realize what a liability he is. It's not even that he's projecting his own rational thinking, since we know he doesn't sacrifice his own friends just to survive.

7/ The lieutenant in the rear looks a little like Hyoga, but the timing's not right!
This flashback scene happens before Gen met Senku, and Gen showed up in Ishigami Village to eat some ramen about 6 months prior to Hyoga+Homura's attack.

7B/ However, Hyoga's flashback tells us he was revived only 1 month prior to the attack on Ishigami Village!
Which means, unless this is a continuity error, both these lieutenants are new characters who got revived very early on. Before anyone else in this spread, basically.

8/ Gen's still a bit of an enigma (hopes? dreams? backstory?) but now we know he really admires the ability to count to a big number. Was he planning on betraying Tsukasa from the day he saw the date on the tree? Because he knew there was a cooler dude out there?

9/ In a world where shonen characters often have punny birthdays, I should've seen this coming!

10/ A few weeks back, I was a doofus and forgot about the tree date + counting-of-seconds, and @radicalnumber6 helpfully reminded me and pointed out that we did have all the numbers we need to figure out Senku's birthday, just like Gen did in the story!

11/ I came up with January 29th, she came up with January 5th (she was much closer, obviously!) and explained to me an odd fact about how leap years work. A fact that accounted for my error, since I was doing this by hand instead of with a date calculator, because I am not smart.

12/ A year is actually 365.25 days, which is why we add a day to February every 4 years, right? Not quite! Turns out that actually overcompensates by exactly 3 days every 400 years, because the true length of a year on Earth is only 365.242199 days.

13/The Gregorian reform of the calendar fixed this verrry slow drift from accuracy by declaring that century years (1800,1900,2000,etc.) are only leap years if divisible by 400. Meaning, 2000 was a leap year, but 2100 will not be. That eliminates the extra 3 days every 400 years.

14/ Now we have all the data!
-Senku is 6,268 (living) days old on December 31st, 5739 (he hasn't "lived" through January 1st yet).
-Breakout date was April 1st, 5738
- He was petrified for 117,354,893,870 seconds

15/
4/1/5738-->12/31/5739 is 639 days.
6,268 - 639 = 5629 days lived pre-petrification
117,354,893,870s/ 60s/m / 60m/hr / 24hr/d = 1,358,274.2346 days
Going back from 4/1/5738 that many days, taking into account all the leap year nonsense, we get...

16/ Petrification date was Monday June 3rd, 2019. Mark your calendars.

Senku lived 5,629 days up to that point, making his birthday January 4th, 2004.

17/ So we're supposed to believe that Gen Asagiri knew the weird leap year thing, did all that math by hand in the dirt, and somehow got the right answer. Uh-huh.

Or maybe he just realized it must be January 4th because of the ishi/stone pun.

18/For fun, that extra .2346 days is 5h37m50s.
That's the difference, re: time of day, between Petrification Moment and Senku Breakout.
So if the stoning happened at 10 am, say, Senku broke out at 3:38 pm.
Japan does not do DST, nor would it matter (dates are in April and June).

17B addendum/
Gen didn't know the # of seconds Senku counted, of course. What he did know was the petrification date (that kind of thing would stick in your mind, yeah?), which substitutes for that missing data.

17C/ ...which means he didn't have to know the leap year thing after all! Slightly more believable that he arrived at the correct answer.