Lecture 2 - Deep Time Agriculture

Geology and History (the Long View)

The key driver of global change at the longest scales is plate tectonics, one of the most beautiful - and simple - theories in science

→ the earth’s crust is divided into a series of plates, that “float” on a mobile layer (the mantle) beneath

Impact on Life

• Tectonics produces geological processes that change life (or its environment)…

• …this can leas to Mass Extinction events’ five of them throughout earth’s history, four of which were likely caused by geological phenomena

Astronomical Impacts on Climate

• Astronomical phenomena can also affect the earth’s climate:

- The earth’s axial tilt changes over thousands of years (from 22.1° to 24.5°)

- The earth’s axial direction changes due to precession (wobbling like a child’s spinning top as it slows down)

- The eccentricity of the earth’s orbit (it’s not a perfect circle, but a very slight ellipse) around the sun can change slightly, affecting solar intensity

- (Controversially) – the sun’s output might change over time

• All these taken together are known as Milankovitch Cycles and they are well-established as drivers of climate change over long periods

Why is a “Long View” of history important to Environmentalism?

• Are we a virus? Can we live in harmony with the natural world?

• Well, what does that mean? Harmony how? What is “natural” in the natural world?

• A “long view” of history leads us, perhaps, to some startling conclusions about the relationship between humans and nature

Holocene Environmental History - Definitions

• Holocene = now; the period since the last retreat of the polar ice sheets from the Pleistocene period (Pleistocene = the last 2.5 million years, give or take)

• Holocene + Pleistocene = Quaternary Period

• Holocene = the last 11,500 years or so … a very short measure of time... but it contains all of recorded human history, and all of human settled civilization

• Anthropocene = period in which humans are dominant drivers of planetary change (era not yet officially approved, nor is its start date nailed down yet)

Consequences…

• So: modern humans are spreading as the ice is retreating. What then, is the nature of the environment into which humans spread? Is it pristine? Or does it evolve hand-in-hand with humans

• Thus, the idea of pristine environment may be incorrect

Firestick & Other Technology: Holocene Environmental Impact

• Humans used fire far more widely than earlier thought

–Cooking (obviously)

–Land clearance

–Silviculture

• Domestication of animals affects Holocene fauna

So: 99% of Human History: Hunter-Gatherers

• Subsisted in locally-available resources, or travelled to find them

• Human advantages:

  - intelligence

  - communication ( = culture)

  - fire employment

  - diet

  - toolmaking

Hunter-Gatherers: Modes of Existence

• Great social advantage: their flexibility

• Exploit many resources lightly, not depend heavily on only a few

• Typically mobile, either seasonally or constantly

• Little opportunity for economic or other specializations to develop

Pastoralism…a “bridge” to agriculture?

• Emerges around the same time as agriculture (about 14,000 to 12,000 years ago)

• It is the herding of domesticated or partially domesticated animals

• Nomadic, wandering mode of existence

• Usually based on marginal land; was compatible or even interdependent with agriculture…

• …but also led to conflict, i.e., warfare

The Emergence of Agriculture

• Sedentism = living in one place; it’s new for humans

• 12,000 - 10,000 years ago, villages began to appear, esp. in what is today the Middle East

Emergence of Agriculture - Specific Theories

• Was it population concentration produced shortages, leading to necessity of agriculture

• Was it …”Garbage Pile” model?

• Was it …(Current champion) → climate change stress on the Natufian Culture of the Fertile Crescent, forcing them to become agriculturalists?

Younger Dryas

The “Younger Dryas” is named after this lovely little plant, Dryas octopetala, a flower typical of cold, open, Arctic environments.

A Half a World Away…

Around 12,800 B.P., Lake Agassiz in N. America (covering parts of Manitoba, N. Dakota, Minnesota, Ontario, Saskatchewan and fed by glacial meltwater) bursts its banks in a massive, immediate episode…

…which produces the Younger Dryas (maybe)

The Impact of the Younger Dryas in the Fertile Crescent

• Cooler, much dryer conditions dramatically limited the productivity of the region

• Natufians had a choice: to become semi-nomadic again (remember – at the onset of the Younger Dryas they were that rare category, sedentary hunter-gatherers), roaming in search of food…

• … but some of them remained semi-sedentary, and began to cultivate some plant species (einkorn in particular) to preferentially help them thrive

• By the time the Younger Dryas ended, around 11,500 B.P., agriculture was firmly established in the Fertile Crescent – and humanity was changed forever

Environmental circumstances affecting us… why domesticate Einkorn wheat?

• Brittle vs non-brittle rachis in einkorn wheat, and why this matters

• One gene, one mutation, in one location in the Middle East, about 12,000 years ago in today’s southern Turkey… spells death for the plant

• …or it represents the most important event in human history. You pick.