After being told of mankinds history of scientific progress, Chrome sheds tears over the fact that the vast knowledge and achievements humanity had obtained through millions of years of research all vanished in one day.
It might only be a few panels, but Senku crying over Byakuya's grave is somewhat depressing.
To add context: Not only is Senku crying over the grave of his father, who has been dead for thousands of years: is also the death of the coolest dad ever, the same man who sold almost everything to help a young Senku accomplish his dream. The fact this man had so much faith in his son to even left him a message to the distant future (Which could have been lost, but by chance of miracle it didn't) is just shockingly optimistic. Byakuya is the coolest dad ever.
There's also the fact that up to this point, Senku had only really expressed overall enthusiasm, shock, frustration, and anger at everything. Even when talking about reviving humanity he sounds more determined than anything. Here, we see Mr. Awesome Ego in grief to the point of tears.
Chapter 83: After all they've been through fighting each other, Senku and Tsukasa have an honest, ordinary conversation while Senku gets ready to kill Tsukasa in order to put him in cryogenic stasis.
Chapter 115 finally reveals how Byakuya died: He spent the rest of his life, even after his fellow astronauts had all died, panning a river for rare metals so that he could store them in a "time capsule" and send them to Senku. Eventually his body gave out and he collapsed, gazing at the reflection of space in the water. Then he caught sight of the International Space Station, still visible in the night sky, and shed a Single Tear before passing on, thinking of his son.