No historian seriously questions that the European invasion of the Americas resulted in millions of deaths. The serious debate has been how many millions. What if it was enough millions to change the carbon dioxide (CO2) content in the atmosphere and therefore the climate and ultimately the geology of the Earth?

Simon Lewis and Mark Maslin, British geographers writing in Nature, have proposed that a massive die-off of Indigenous Peoples in the Americas has left enough permanent global evidence to define a new geological epoch, the Anthropocene. In this seminal study, they examine the Industrial Revolution and the detonation of atomic bombs as potential geological markers.

The Industrial Revolution, they conclude, happened too unevenly to provide worldwide physical evidence pointing to a reasonably specific date. The atomic bomb arrived in 1945 with worldwide geological evidence of permanent change peaking in 1964.

Lewis and Maslin reject 1964 largely because the date is so recent that the changes that began in 1945 are still playing out. I would add that the international treaty banning atmospheric nuclear tests went into effect in 1963, and the geological impact of radiation can be radically changed by new countries joining the nuclear club or a war breaking out among the current members. Either of these events would destroy the geological usefulness of 1964.

This leaves the collision between the so-called Old World and New World, which Lewis and Maslin claim caused a dip in atmospheric CO2 that is measurable in many ways worldwide. All measurements point to 1610 as the low point in the dip. The cause of the dip has a great impact on historians’ arguments over American Indian body count from contact with Europeans. While this evidence does not quiet disputes about the intent of the colonists, modern Indians would consider just knowing the approximate body count from physical evidence an improvement in the historical narrative.

How do dead Indians cause lower atmospheric CO2? If we all met the stereotype of hunter-gatherers before Europeans showed up, a die-off would not have a global impact. A charitable view of that stereotype would be that it was a mistake caused by more hunter-gatherers surviving European diseases because, unlike their sedentary farmer cousins, they had very little direct contact with the colonists and therefore less opportunity to be infected.

When farmers die off, their fields go fallow. When the fields go fallow, forests take over, and forests are gigantic carbon sinks, sucking up CO2. Theoretically, if the deaths were enough to move the CO2 in the entire atmosphere, it ought to be possible to “reverse engineer” the body count. Lewis and Maslin started with body counts that match existing scholarship.

The calculation in the Nature article is that the European invasion caused the deaths of approximately 50 million people farming 1.3 hectares per person. Removal of that many people from that much land should sequester between 7 and 14 petagrams of carbon over 100 years, the difference in numbers having to do with how much of the farming was "slash and burn" agriculture, which gives off more CO2.

They suggest that maximum human mortality would happen decades after first contact in 1492 and maximum carbon uptake from the fallow farms would take another 20-50 years, suggesting a date between 1550 and 1650. Ice core CO2 measurements narrow the date to 1610.

This is not a completely abstract dispute. Lewis and Maslin are arguing for recognition of a Global Stratotype Section and Point (GSSP, less formally known as a “golden spike”) and/or a Global Standard Stratigraphic Act (GSSA). Recognition of these markers requires a consensus in the scientific community.

In 2013, the International Union of Geological Sciences (IUGS) convened a group of scholars charged to decide by 2016 whether the Holocene is over and the Anthropocene has begun. The best evidence of that is a “golden spike,” and the Nature article is aimed at convincing the IUGS that we have a consensus.

Once that consensus is reached, the collision of Europe and the Americas becomes the working paradigm, the method of describing research going forward. What is at stake is the boundary of the Anthropocene, the epoch of humans. From our point of view, genocide will be recognized as a source of anthropogenic climate change. Since the climate change happened, the genocide will be impossible to deny.