Norse and Aztecs quiz: 8 questions

The warmth was regional. Mann and colleagues found the North Atlantic warm while parts of the tropical Pacific were cool, which is why scientists speak of an anomaly and why its effects varied from coast to coast.

The clinker hull flexed with the waves and drew only about a metre of water, so crews could cross open sea, row up rivers and beach anywhere. Its woollen sail cost years of women’s labour.

A burst of cosmic radiation left a radiocarbon spike in every tree ring formed in 993. Kuitems’s team found it 29 rings inside the bark on three cut pieces of wood, so all three trees were felled in 1021.

Arneborg’s studies show marine protein rising from about 15–50 percent at settlement to 50–80 percent by the end, with seals dominating the rubbish heaps. The Norse adapted far more than the old stereotype allows.

Stockfish kept for years without salt and fed markets in England and the Hanseatic towns. Cod thrived in the cold, so the trade survived the climate that helped end Norse Greenland.

In a closed basin water leaves only by evaporation, concentrating salts in the lowest lake. The spring-fed south stayed fresh, which is where the great chinampa zone lay.

The tribute pages list each province’s towns and goods in painted symbols with Spanish notes. Historians still debate whether many symbols mean single items or loads of twenty.

The gaps kept the lake’s waters connected and gave the city a defence. In the retreat of June 1520 and the siege of 1521 those same gaps became deadly obstacles.