As The Earth Warmed after the last glacial maximum, temperatures fluctuated. About 9700 B.C.E., temperatures rose again suddenly and began to stabilize, marking the beginning of a new geological epoch, the Holocene. The landscape continued to change, but not so fast that a single generation of humans would have noticed. Ice- sheets and tundra were receding in Eurasia, and over time human groups, both hunter- gatherers and then early farmer- pastoralist communities, adjusted their ways of living to warmer conditions and different rainfall patterns. Small- scale farming and herding emerged on all nonpolar continents during the period 8500 to 6000 B.C.E., predominantly in the northern hemisphere, while human numbers were creeping up. These great changes in environmental conditions and subsequent cultural practices had a profound influence on the foundations of human health and survival: food sufficiency and quality, water supplies, contacts with infectious agents, modes of settlement, and social relations. A new era in human ecology was looming. Farming increased food production, but the switch to dependency on a few staples decreased diversity of diets and created an annual agricultural regime more susceptible to climate shifts. Close contact with animals, standing water in irrigated environments, and denser settlements provided opportunities for microbes, pathogens, viruses, and parasites to cross species barriers and infect and spread among human populations. During the Early Holocene, from about 9700 B.C.E. to 6000 B.C.E., the earth was subjected to the competing stresses of high solar influence and still massive melting ice- sheets. From around 6000 B.C.E., the majority of ice- sheet melting had abated, allowing the stabilization of the Earth’s climate into what can be called the Mid- Holocene Climatic Optimum (approx. 6000 to 3000 B.C.E.). This was a change in climate that spanned 3,000 to 4,000 years. Warming was most evident in the northern hemisphere, influenced by the peaking of solar radiation at higher northern latitudes as the 23,000- year Milankovitch “wobble” cycle maximized northern sun exposure for several millennia. The Milankovitch cycle also drew the rain- bearing Inter- Tropical Convergence Zone (ITCZ) further north.
Imaging of Uranus and Neptune
