About block 3,900
Bitcoin block 3,900 was mined by Unknown on February 11, 2009 at 4:17 PM UTC, 17 min 29 s after block 3,899. That is slower than the 10-minute target; long gaps are normal, since every hash attempt is an independent draw with the same tiny chance.
It confirmed 1 transactions in 0.00 MB (0.0% of the 4 million weight-unit limit). The median transaction paid 0.00 sat/vB, and all fees added up to 0.0000 BTC. With the 50.000 BTC subsidy of halving era 1, Unknown earned 50.0000 BTC for this block.
Block 3,900 is number 1,885 of 2,016 in difficulty epoch 1; 131 blocks remain until the next difficulty adjustment at block 4,031. The next halving is at block 210,000, 206,100 blocks after this one.
Its hash starts with 8 zeros: that is the proof of work, a number below the target that the whole network’s hashrate had to search for. Unknown found 20 blocks in the week before. Today the block has 970,292 confirmations, so it is settled beyond any practical doubt.