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The Holocene

Earth Science Lecture 18

Elanor Alun

What is the Holocene?

The current interglacial period, characterised by humans becoming the dominant species on the planet and our subsequent impacts.

Also: anthropocene, capitalocene.

Humans have caused steady change since we emerged (unusual)

Timeline

Timeline

Not always easy to separate impacts of nature and people

7,500 yrs BP

2,500 yrs BP

5,000 yrs BP

10,000 yrs BP

Present day

Nature: Tamed

5,000 - 500 yrs BP

Modern Era

500 yrs BP - now

Early Holocene

10,000 - 5,000 yrs BP

Pleistocene Prelude

>10,000 yrs BP

  • environmental decline
  • pollution
  • climate change
  • ice age
  • megafauna extinctions
  • human ecology/spread
  • physical changes
  • return of forests
  • human ecology/spread
  • agriculture
  • cultural development
  • human expansion to peripheries

Pleistocene Prelude

>10,000 yrs BP

Dominated by deglaciation, as the Earth warmed from the previous ice age

Also the beginning of the rise of a new dominant species - humans

Deglaciation

Deglaciation

Unsteady process – not all at once, and with some minor readvances in ice sheets. This happened at different times around the world.

Interstadial (warming bit) 13,000 – 11,000 ybp; then stadial (cooling bit) 11,000 – 10,000 ybp. Then back to warming.

The Interstadial

The first response was insects, not plants – beetles are a great proxy because of their thermal preferences

Plants need soils to be right, and pre-13,000 ybp the soils were still thin. But then in come grasses and sedges (fast-growing, competitive, like open habitats.)

Followed by shrubs (juniper (Juniperus), willow (Salix) and crowberry (Empetrum)); in Wales and southern England, followed by birch woodland (Betula pubescens most important.)

The Stadial Onwards

During the stadial, Scotland became completely iced over again. New ice cap formed the ‘parallel roads’ at Glen Roy.

Woodlands retreated again. Climate is cold and dry, Britain a tundra.

BUT was it global or regional?

Regional, primarily; limited to western Europe, though some tropics and sites in Africa were affected by dryness at the same time, so some climate instability.

But by and large, the Earth warmed up.

Human Ecology

Human Ecology

So the Homo genus first stands up and starts getting stabby with the pointy things about 5 million years ago – but when do they migrate?

Taking the latest agreed-upon dates (NOT earliest possible):

  • Half a million years ago, they spread to adjacent continents – Asia and Europe
  • 40,000 years ago, they somehow sail by raft/canoe over 100km to New Guinea, and from there to Australia
  • 12,000 years ago, they reach the Americas; poss sooner? Before the land bridge of Beringia sank, could walk Asia-Alaska. BUT, the way south was then blocked by the North American ice sheets, so further expansion impossible until interglacial.
  • 3,000 – 1,000 years ago. Finally, the periphery, i.e. hard-to-reach places: Arctic, Pacific islands, New Zealand and Madagascar

Species Ecology: Humans (Pleistocene)

At this time, human economies are subsistence ones – hunter-fishing-gatherer (h-f-g.)

More hunting than gathering at this point, because tundra vegetation is limited (this changes dramatically in the Holocene).

H-f-g bands are migratory, and need large territories to move with the resources; >75km per 25 people. Very low population densities, so very low population; about 10 million globally by end of Pleistocene.

Stone age tech, and low population, so limited impact environmentally at this time. Main one: fire, to clear vegetation OR encourage regrowth.

Megafaunal Extinction

At this point, lots of large animals; body weight of >44kg, usually mammals.

We recognise a lot as big versions of current animals

 A huge number of these went extinct at the end of the Pleisticine/early Holocene in a mass event – unusually, it specifically selected large animals. Why?

Environment

Environment

The world was warming, so various impacts:

  • Woodland expansion would have reduced herbivorous habitat

  • Temps harder for woolly species to cope (and they changed rapidly; poss ~10 degrees per decade)

  • Disease

  • Large animals often less able to adapt to environmental pressures and changes

Human Impact

Human Impact

Big game hunting was a vital part of human behaviour.

Humans are cache killers (like dogs, cats, mustelids, etc)

Large mammals frequently died out within a few centuries of human colonisation

Universally Applicable?

Problem is, while this can be argued for many... doesn’t work for all. Europe, Asia and Africa all see humans and megafauna coinciding for thousands of years before drop off.

Africa barely has a phase of extinctions at all, in fact, until the preset day

Also, often the most well-represented animals at kill sites are ones that are still around (bison, reindeer, etc.) But then, maybe farming.

Early Holocene

10,000 - 5,000 years BP

Era of marked change as climate rebounded from ice age - ecology and environment are all about adaptation to that change

Early Holocene

Physical Changes

This is largely the period that the modern state of the physical environment comes about.

Took a while for the northern hemisphere ice sheets to retreat because of their sheer mass. The Laurentide ice sheet had its heart removed by about 8000 years ago when the sea entered Hudson’s Bay.

Sea Levels

Sea Levels

Between 10,000 – 5000 years ago, eustatic sea levels rose ~40m to roughly modern day elevations.

Some places saw land rising from isostatic rebound (40+ metres in bits of Scotland; many times that in Scandinavia)

Sinking Land

Netherlands had the opposite problem – like a see-saw.

And lands drowned. The Sunda subcontinent became the islands of Indonesia; the Beringia land bridge sank; and lots of myths abound of drowned land (Atlantis, Cantre-r Gwaelod, etc)

Other Developments

Water Features

Lakes develop! Filled with glacial melt. But sediments and plants both arrive and develop them.

At this stage, rivers are mostly overpowered by the sea - saline channels to land

The progression from lake to reed swamp to fen is called a hydrosere, but it’s less stable than plant succession.

Soils

Soils also developed in this time through freshwater, humus, better aeration/thermal inputs, etc.

Depending on inputs – including erosion and bedrock type – they developed distinct profiles that many continue today.

Return of Forests

Return of Forests

We can actually map this remarkably accurately thanks to pollen analysis.

Pre-Holocene, many trees were in ‘glacial refuges’

Once climatic conditions were amenable and soils prepared, the only checks on tree expansion were rate of dispersal.

Also position of glacial refuges – pine recolonised northern Europe faster than beech because it started closer.

Dispersal Factors

Wind dispersal obviously gives some spp (birch, elm) an advantage over those that need outside agents like birds, streams etc (oak).

Growth rate and age of first seed setting – birches beat oaks

Over 500-2000 years, opportunistic spp like birch, pine, alder and hazel spread at rates of 1-2km per year in Europe

In North America it was around 0.5km per year; so, perhaps competition with spruce slowed deciduous trees?

Case Study: Europe

10,000 – 8,000 years ago – CHAOS. Trees everywhere!

A lot of weird, short-lived communities for which we have no modern analogue; trees just grew and died wherever they could, and it took a few millennia before they worked out what worked.

By 8000 years ago, biomes were modern – boreal forest in the north, deciduous domination, and tundra-steppe pretty much gone.

Took much longer for species composition to settle. Birch and pine were followed by hazel and elm, both of which expanded in about 500 years. Oak, lime, alder and ash afterwards. Others didn’t reach their extents until the last millennium, and some might still be expanding now (spruce).

Human Ecology

Human Ecology

In terms of diet:

  • Thanks to the forests, gathering becomes a major part of h-f-g life; it’s less dangerous, even children can do it

  • Fruits, nuts, greens, fungi, fern rhizomes, seeds, spices, and even medicines

  • Stone pine nuts actually provide two thirds the protein of lean steak.

  • Still hunting, but much more omnivorous now.

Consequent Behaviour

In Europe, communities seem to gather together at lowland sites over winter, and then migrate in smaller families to the uplands in summer.

In north Africa, the Sahara was a network of lakes and savannah. H-f-g people ate hugely varied diets of aquatic food and snails. But, in present-day Egypt, there’s very early evidence of cattle species kept.

Burning still the main tool used for management (to encourage grazing areas); but, also others

European Mesolithic sites have unusually high amounts of ivy pollen, planted to attract red deer.

People (esp. in Mexico) learned to use resources all year round, so they could start stying in one place.

Basically- the precursor to farming.

Nature: Tamed

5,000 - 500 years BP

The era that sees the biggest shift in human development, including advanced societies

This is when the swing from ‘nature-dominated’ to ‘human-dominated’ happens, but obvs, still with natural input - hard to separate

For example, sub-tropical northern hemisphere desiccated at this point – led to the oasis of the Nile becoming super important to human ecology. Humans went from an aqualithic culture to developing new, intensified forms of land-use.

Agriculture

Agriculture

Outside of Europe, there are multiple centres of origin for agriculture around the world.

The three great grain crops – wheat, rice and maize. These three formed the new staples of human diet (and still do).

Not until 500 years ago that farming took on global distribution, i.e. crops were spread to greater areas and intermingled.

Allowed the move from migration to sedentism – major shift in human culture and ecology.

Why?

Energy involved in farming (land prep, sowing, weeding, harvest etc) often makes agriculture more intensive than wild harvest, for about the same inputs. So, what was the incentive for humans to develop it?

Most likely, there must have been some shift in the balance of populations and food resources. Population increase, or environmental change.

This is likely to have been opportunist.

Early humans, by this point, were good at adapting to whatever was around; as arable land and animal numbers grew, we began to domesticate them.

Hence it developed in many places separately, along different paths (e.g. in the Middle East, animals are way more important at first than plants; in Europe/middle east they quickly stopped gathering wild plants, but not so in Mesoamerica, etc)

Early Impacts

Species change (selection for human use.) Maize, wheat, etc – plant organs emphasised. Many can’t wild propagate now, and so rely on us (and we rely on them.)

Species distribution. Agricultre allows protection from predators, and increases competition ability. Predators (e.g. wolf) and competitors (e.g. aurochs) killed, both directly and indirectly through habitat loss.

Land use. Existing vegetation must be cleared. First substantial human impact on soil. More permanent, because more sedentary.

Physical Developments

Physical Developments

Rivers finally become strong enough to reverse the tide against the sea - freshwater streams leading to ocean.

This leads to shorelines expanding as sedimentation at deltas occurs.

Peat bog development – hard to know how much was climate and how much was human interference, but peat formation requires waterlogging of the soil (something tree cover reduces/removes.) One peat forms, trees can no longer grow there.

Agricultural Impacts

In addition to woodland clearance and marsh drainage, marginal land got cultivated – susceptible to soil erosion.

Artificial control of hydrology – this begins with technology like the shaduf on the Nile, but progresses into dams, irrigation channels, aqueducts, wells, etc.

Agricultural terraces arrive in some cultures (e.g. Asia (rice), the Mediterranean (Greek domi), South America (Incas, Peru) and Africa (various). These allow for water retention, and crops where they otherwise wouldn’t grow on hillsides.

Small ecosystems develop. Extensive rice fields along Chinese river valleys, olive groves in the Mediterranean, etc

Human Ecology

This era saw huge development, both culturally and in terms of species spread.

Human Expansion

Cultural Development

Cultural Development

And then, the first major civilisations arose: Egypt, Mesopotamia, India and China

All of these developed in a specific physical context: a major alluvial river valley, with a climate of low/unreliable rainfall

  • The Nile
  • The Tigris-Euphrates
  • The Indus
  • The Yellow River

Advanced human civilisation required limiting factors that needed to be overcome, which stimulated technological advancement

In this case, large-scale manipulation of water and soil – this meant hydraulic irrigation schemes, under a centralised organisation.

This organisation – a ruling class – controlled timing/distribution of irrigation water, collection/storage of surplus food, infrastructural maintenance… And thus, ancient civilisations were born.

Human Expansion

Human Expansion

In addition to the big inventions of pastoralism and urbanism, this era also saw the last big human expansions – the Arctic, and the Pacific.

Arctic

A stressed ecosystem, including for humans.

As the ice sheets retreated, the modern tundra zone developed north of the boreal forest zone; Arctic sea became seasonally frozen.

First half of Holocene had seen some h-f-g sites around Alaska and Northern Yukon (land bridges), but second half saw the development of Arctic maritime culture and technology.

Dorset and Thule cultures were the ancestors of the Inuit – same tech (snow block houses, stone lamps, kayaks, and harpoon hunting of seal and fish).

Inuit adapted highly successfully, in fact – Viking settlements in Greenland were abandoned by 1500AD, and saw Iceland almost entirely deforested.

Meanwhile in northern Eurasia, reindeer herding became the lynchpin of cultural development.

Pacific

3500 – 1000 BP, virtually all Pacific islands came to be settled by seafaring peoples in two big surges.

  • 3500 – 3000 BP, Lapita culture expanded over Melanesia and western Polynesia.

  • 2100 – 1100 BP, the early Polynesians spread from Fiji to Marquesas, then split three ways – north to Hawai’i, east to Easter Island, and south to New Zealand.

Pacific islands are good case studies for assessing human impacts on ecosystems (although have to remember – most didn’t have indigenous animal populations before us.)

There is evidence to suggest that early Polynesian sea farers were also trading with South America (sweet potato, Easter Island statues, etc)

They took plants and animals with them to new shores, to set up agriculture – dogs, chickens, pigs, coconuts, taro, yams, bananas and breadfruits.

This agricutlure was supported by wild resourses – fishing esp.

Once established, culture followed agriculture – it’s all according to resources. On big islands like Hawai’i, agri was super productive (even involving irrigation) – tribal chiefs held control similar to English feudal lords.

Smaller islands saw cultural reversal. Many Lapita islands lost pottery making, many lost canoe building and trade and therefore became isolated. In some cases, this led to settlement collapse.

eg – Pitcairn. Mutineers from the Bounty landed in 1790AD and found coconuts and breadfruit being cultivated, stone platforms and statues... but no people anywhere at all. Became known as the Mystery Islands.

Case Study: New Zealand

One of the very last to be colonised.

NZ climate moist subtropical/cool temperate, so PERFECT for All Of The Trees.

But, When Captain Cook arrived, half the island was treeless. Some above the natural treeline (obvs), but majority was lowland scrub, fern or tussock grassland. These soils show abundant charcoal and wood, and pollen analysis confirms that, prior to Polynesian settlement, only a limited, low-rainfall area of central Otago couldn’t support continuous tree cover.

Deforestation began 1000 BP, was most severe 800 – 600, but evened out about 200 years before Europeans came (and made it much worse).

Interestingly, not just done for farming – Maori agriculture centred on North Island, but most trees lost on South Island – why?

Partly tree type – southern beech (Northofagus) is slow to recover post fire.

 But also, Maori diet included things like bracken rhizomes, so deforestation needed to grow bracken. No trees meant it was easier to hunt giant moa, too

Modern Era

500 yrs BP - now

Unlike previous eras of the Holocene, this block has a quantum leap in human-induced change. Hard to separate human from climate previously, but in 500 years it’s almost all been human – including the climate itself.

The major contributors: European expansion, Industrial Capitalism.

European Expansion

European Expansion

End of discrete crop cultures. Europeans moved things around the world. Sometimes this made acceptable analogues in different locations, e.g. vinyards in California. But many times not, e.g. vinyards in Australia. Species we now consider native:

  • Irish potatoes
  • Italian tomatoes
  • Australian dingos
  • Canadian wheat
  • Native American palomino ponies

Animals

Animals have sometimes been worse than plants. In North America, few domestic animals before 1500AD (and natives a bit species poor after megafauna extinctions). But now, cattle, sheep, pigs and donkeys all feral. Donkeys brought over during gold rush – now out-compete native pronghorn antelope.

Other animals extinct or near-extinct, either intentionally (bison) or not (passenger pigeon). Even higher extinction rates on islands, e.g. dodo.

Case Study: Porto Santo

Porto Santo near Madeira was almost entirely destroyed by Columbus’ father-in-law introducing a single female rabbit and her offspring. The impact was so bad the entire isand had to be abandoned. Madeira itself means ‘timber’, and now is almost completely deforested thanks to Portuguese settlers.

Industrial Capitalism

Industrial Capitalism

Starting with the industrial revolution. Now everything is mechanised; this further removes people from the land, and farmers no longer see land as a habitat they’re part of, but a set of resources to harvest.

Profit is maximised over sustainability, so degradation is inevitable; esp soil erosion. When this combines with European expansion, the effect can be catastrophic. e.g. the Arkansas Dust Bowl.

Pollution inputs have gone through the roof. This leads to impacts like acid rain/soil and water acidification, eutrophication, pollution events that damage/destroy life, etc

CLIMATE CHANGE OH NO

Overpopulation

Overpopulation

We produce enough food for ten billion, currently

Under capitalist systems, mega-producers (e.g. the US - chicken, soy, corn, beef, etc) literally have to destroy quantities of the food they produce to prevent it devaluing

"Where women are given the rights over their own bodies; where they have political independence; where they have medical facilities to enable them to control the number of children they bear; where they are literate; where they have the vote; When those things happen, the birth rate falls." - David Attenborough

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