Ballpark
Puzzle #27 · 16 October 2026
The five questions from that day's Ballpark, each with its answer, the fact behind it and a link to the source. Rather play it first? It is in the archive.
1. According to a study cited by NOAA, how many metric tons of seawater contain just one gram of gold?
100M metric tons
About 100 million metric tons of water per gram of gold, in the Atlantic and north Pacific. NOAA says there is no cost-effective way to extract it. Source
2. About how many species live on Earth (bacteria not included), according to a widely cited 2011 estimate?
8.7M species
About 8.7 million, give or take 1.3 million. Only about 1.2 million had been catalogued, so some 86% of species still await description. Source
Image: Henk Caspers / Naturalis · CC BY-SA 3.0, cropped
3. How many years ago did "Lucy", the famous early human ancestor found in Ethiopia, live?
3.2M years
About 3.2 million years ago. Found in 1974, she was nicknamed after the Beatles song Lucy in the Sky with Diamonds, playing in camp that night. Source
4. What is the generating capacity of China's Three Gorges Dam?
22,500 megawatts
22,500 MW, the world's largest hydroelectric plant. Brazil and Paraguay's Itaipu Dam has 14,000 MW. Source
Image: Le Grand Portage · CC BY 2.0, cropped
5. What is the smallest number of starting clues a valid Sudoku puzzle (one with a single solution) can have?
17 clues
17 clues. In 2012 researchers ran an exhaustive computer search for 16-clue puzzles and found none, proving a long-held conjecture. Source
Image: Héctor Rodríguez · CC BY 2.0, cropped