Did this rejoining of two branches of humanity after 12,000 years of separation change Earth’s history as well as human history? The global mixing of humans and their deadly diseases is just one aspect of a much larger global biological mixing that the historian Alfred Crosby called the Columbian Exchange. Not only did pathogens travel, so did plants and animals. Species moved from one continent to another, and one ocean basin to another, outside their evolutionary context. This led to a globalization and homogenization of the world’s species, which continues today.

Most dramatically, the Columbian Exchange transformed farming and human diets. This change is often so culturally ingrained that we take it for granted. It is difficult to conceive that in Europe there were no potatoes or tomatoes before the 16th century; in the Americas, no wheat or bananas; no chili peppers in China or India; and no peanuts in Africa. The transformation of diets was near total: even deep in the Congo rainforest, the staple is cassava, a plant originally from South America, while deep in the Amazon rainforest the Yanomami eat plantains, which were domesticated in Africa.

Farmers, from the 16th century onward, suddenly had a much greater number of crops and animals to choose from. The best crop for the local environmental conditions, sourced from anywhere in the world, could now be planted. People picked the ones that worked well, incorporating them into new farming systems. The increase in the diversity of crops planted in any one place was also a boon to farmers worldwide. These new crops not only improved yields. In China, for example, the arrival of maize allowed drier lands to be farmed, driving new waves of deforestation and a large population increase.

A new history of the first peoples in the Americas

Despite the transport of new killer diseases, including the emergence of deadly syphilis in Europe and Asia, which was linked to trade with the Americas, the Columbian Exchange eventually allowed more people to live off the land. These newly available plants and animals led to the single largest improvement in farm productivity since the original agricultural revolution. The results of different peoples’ efforts in domesticating and refining crops over thousands of years were now available and being adopted worldwide. A single globalized farming culture was born.

In geological terms, transcontinental shipping, which began in the 16th century, and later aviation, which took off in the 20th century, are playing the same role as plate tectonics has in the past. Today, they are knitting the continents and oceans together, the opposite of the trend over the past 200 million years that has seen the continents separating. When geologists inspect the geological record millions of years in the future, fossilized species will be recorded as instantaneously arriving on new continents and in new ocean basins. These fossilized species that humans have allowed to jump geographical barriers will give the appearance of a new species having evolved, just like in other epochs in Earth’s history. But there will also be a subtly different pattern. Normally in the geological record there are extinctions, which in turn create vacant niches, which evolution fills with new, often quite different-looking species. In the human epoch, the sudden appearance of species that have jumped continents, or new hybrid species, will appear in the geological record as being quite similar to already existing species. This homogenization of Earth’s biological diversity is one key hallmark of the Anthropocene, with no obvious past analogue in Earth’s history.