Quotes & Sayings


We, and creation itself, actualize the possibilities of the God who sustains the world, towards becoming in the world in a fuller, more deeper way. - R.E. Slater

There is urgency in coming to see the world as a web of interrelated processes of which we are integral parts, so that all of our choices and actions have [consequential effects upon] the world around us. - Process Metaphysician Alfred North Whitehead

Kurt Gödel's Incompleteness Theorem says (i) all closed systems are unprovable within themselves and, that (ii) all open systems are rightly understood as incomplete. - R.E. Slater

The most true thing about you is what God has said to you in Christ, "You are My Beloved." - Tripp Fuller

The God among us is the God who refuses to be God without us, so great is God's Love. - Tripp Fuller

According to some Christian outlooks we were made for another world. Perhaps, rather, we were made for this world to recreate, reclaim, redeem, and renew unto God's future aspiration by the power of His Spirit. - R.E. Slater

Our eschatological ethos is to love. To stand with those who are oppressed. To stand against those who are oppressing. It is that simple. Love is our only calling and Christian Hope. - R.E. Slater

Secularization theory has been massively falsified. We don't live in an age of secularity. We live in an age of explosive, pervasive religiosity... an age of religious pluralism. - Peter L. Berger

Exploring the edge of life and faith in a post-everything world. - Todd Littleton

I don't need another reason to believe, your love is all around for me to see. – Anon

Thou art our need; and in giving us more of thyself thou givest us all. - Khalil Gibran, Prayer XXIII

Be careful what you pretend to be. You become what you pretend to be. - Kurt Vonnegut

Religious beliefs, far from being primary, are often shaped and adjusted by our social goals. - Jim Forest

We become who we are by what we believe and can justify. - R.E. Slater

People, even more than things, need to be restored, renewed, revived, reclaimed, and redeemed; never throw out anyone. – Anon

Certainly, God's love has made fools of us all. - R.E. Slater

An apocalyptic Christian faith doesn't wait for Jesus to come, but for Jesus to become in our midst. - R.E. Slater

Christian belief in God begins with the cross and resurrection of Jesus, not with rational apologetics. - Eberhard Jüngel, Jürgen Moltmann

Our knowledge of God is through the 'I-Thou' encounter, not in finding God at the end of a syllogism or argument. There is a grave danger in any Christian treatment of God as an object. The God of Jesus Christ and Scripture is irreducibly subject and never made as an object, a force, a power, or a principle that can be manipulated. - Emil Brunner

“Ehyeh Asher Ehyeh” means "I will be that who I have yet to become." - God (Ex 3.14) or, conversely, “I AM who I AM Becoming.”

Our job is to love others without stopping to inquire whether or not they are worthy. - Thomas Merton

The church is God's world-changing social experiment of bringing unlikes and differents to the Eucharist/Communion table to share life with one another as a new kind of family. When this happens, we show to the world what love, justice, peace, reconciliation, and life together is designed by God to be. The church is God's show-and-tell for the world to see how God wants us to live as a blended, global, polypluralistic family united with one will, by one Lord, and baptized by one Spirit. – Anon

The cross that is planted at the heart of the history of the world cannot be uprooted. - Jacques Ellul

The Unity in whose loving presence the universe unfolds is inside each person as a call to welcome the stranger, protect animals and the earth, respect the dignity of each person, think new thoughts, and help bring about ecological civilizations. - John Cobb & Farhan A. Shah

If you board the wrong train it is of no use running along the corridors of the train in the other direction. - Dietrich Bonhoeffer

God's justice is restorative rather than punitive; His discipline is merciful rather than punishing; His power is made perfect in weakness; and His grace is sufficient for all. – Anon

Our little [biblical] systems have their day; they have their day and cease to be. They are but broken lights of Thee, and Thou, O God art more than they. - Alfred Lord Tennyson

We can’t control God; God is uncontrollable. God can’t control us; God’s love is uncontrolling! - Thomas Jay Oord

Life in perspective but always in process... as we are relational beings in process to one another, so life events are in process in relation to each event... as God is to Self, is to world, is to us... like Father, like sons and daughters, like events... life in process yet always in perspective. - R.E. Slater

To promote societal transition to sustainable ways of living and a global society founded on a shared ethical framework which includes respect and care for the community of life, ecological integrity, universal human rights, respect for diversity, economic justice, democracy, and a culture of peace. - The Earth Charter Mission Statement

Christian humanism is the belief that human freedom, individual conscience, and unencumbered rational inquiry are compatible with the practice of Christianity or even intrinsic in its doctrine. It represents a philosophical union of Christian faith and classical humanist principles. - Scott Postma

It is never wise to have a self-appointed religious institution determine a nation's moral code. The opportunities for moral compromise and failure are high; the moral codes and creeds assuredly racist, discriminatory, or subjectively and religiously defined; and the pronouncement of inhumanitarian political objectives quite predictable. - R.E. Slater

God's love must both center and define the Christian faith and all religious or human faiths seeking human and ecological balance in worlds of subtraction, harm, tragedy, and evil. - R.E. Slater

In Whitehead’s process ontology, we can think of the experiential ground of reality as an eternal pulse whereby what is objectively public in one moment becomes subjectively prehended in the next, and whereby the subject that emerges from its feelings then perishes into public expression as an object (or “superject”) aiming for novelty. There is a rhythm of Being between object and subject, not an ontological division. This rhythm powers the creative growth of the universe from one occasion of experience to the next. This is the Whiteheadian mantra: “The many become one and are increased by one.” - Matthew Segall

Without Love there is no Truth. And True Truth is always Loving. There is no dichotomy between these terms but only seamless integration. This is the premier centering focus of a Processual Theology of Love. - R.E. Slater

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Note: Generally I do not respond to commentary. I may read the comments but wish to reserve my time to write (or write from the comments I read). Instead, I'd like to see our community help one another and in the helping encourage and exhort each of us towards Christian love in Christ Jesus our Lord and Savior. - re slater

Wednesday, March 8, 2023

Humanity's Evolution During the Climate Changes of the Pleistocene Era




Humanity's Evolution During the Climate
Changes of the Pleistocene Era

by R.E. Slater


I have been slowly moving through man's evolutionary journey towards the times before the Egyptian pyramids when ancient African empires populated the late Stone Age and then migrated from Africa to the Fertile Crescent of Mesopotamia.

As I have learned, the genus homo over the past 7 million years has come-and-gone out of Africa many times criss-crossing the world time-and-again. Which is why some of modern man's evolutionary ancestors may be found as far away as India, China, Indonesia, Oceania, and Australia.

And as I have further been given to understand, the more recent dates of 100,000 years ago or less (50,000 years ago) was where the last great migration of the latest species of homo left Africa, known as homo sapiens, who changed the world and superseded all previous homo variations.

Which doesn't mean that those homo populations scattered about didn't interbreed or develop some form of homo sapien like qualities on their own (sic, the Denisovans?).
"Denisovans may represent a new species of Homo or an archaic subspecies of Homo sapiens (modern humans), but there are too few fossils to erect a proper taxon. Proactively proposed species names for Denisovans are H. denisova or H. altaiensis." - Wikipedia
But however it all came to be I have wanted to know what had occurred before the pages of Genesis had become oral legends. I've generally stated this legendary time to be around 2400 BC before it was written down much later - perhaps as late as between 650 BC - 350 BC. Which is a long time afterwards.

And also by these statements what I am most interested in knowing is how the Late Bronze Age Semitic cultures had come to see themselves and their beliefs as passed down to them by far older civilizations such as the Sumerians in 2500 BC. 

The Hebraic legends of the bible book Genesis didn't happen in a vacuum. It came about as a derivation of a derivation of a derivation from far older discussions of who God was and what this assessment meant to those living then.

In the next several posts I hope to be going through several of the older civilizations of humanity moving from Africa to Mesopotamia as well as along the Levant (the coastal regions of the Old Syrian empire). It'll help us understand where Israel and it's belief fit into the older histories around it.

And then finally towards a general roughing out of the what I would describe as the sociological evolution of faith and religion when visulazing God and today's Christian faith. Which, when I am done, I hope to show that it's ok to re-visualize the Christian faith even as past generations had done and to which is a very old practice of humanity.

For myself, I wish to see God as a God of Love and to better create a (processual) theology of Love from what was handed down to me through the past 2000 years of church history since Jesus' crucifixion.

It also means seeing-through the older beliefs of God-followers as to what are spiritually healthy practices and what are not. Much in church history testifies to the many standards of good and to the healing arts and practices of a loving faith. But there is also in church history that which isn't.

For instance, I consider any form of Trumpian Christianity as sinful, evil, fascist, and useful to the church to dominate and oppress all those it cannot assimilate into it's populist/nationalist faith. As historical example, consider the Medieval Christian Crusades against Jews and Muslims; or, the Spanish/Catholic Inquisitions against heathens and Protestants as being evil forms of faith expression. These were not theologies of Love but theologies of Hate.

For today's final post I am reminded that human evolution was as much shaped by environmental conditions as by interbreeding, genetic-morphology, the development and usage of tool, regional/tribal/familial language development, and so on. If not for these changes homo sapien may never had been... or may have become something else. As it were, human evolution is what it is, as the saying goes in upstate New York when trying to explain the unexplainable. And so we'll leave it at that.

R.E. Slater
March 8, 2023



Our early ancestors evolved on a drying, cooling, and highly variable planet, which has led to competing ideas as to how climate may have shaped human evolution

Equally compelling is the question of how and when humans began to affect their surroundings to such an extent as to become a force of climate change, with disruptions affecting the globe today.

According to earth scientists, paleontologists, and scholars in other fields, the planet has entered a new geological phase – the Anthropocene, the age of humans.

How did this transition of our species from an apelike ancestor in Africa to the current planetary force occur?

What are the prospects for the future of world climate, ecosystems, and our species?


click to enlarge


During the 2.5 million years of the Pleistocene, numerous cold phases called glacials (Quaternary ice age), or significant advances of continental ice sheets, in Europe and North America, occurred at intervals of approximately 40,000 to 100,000 years.

The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years.

The last cold episode of the last glacial period ended about 10,000 years ago.

Over 11 major glacial events have been identified, as well as many minor glacial events.

A major glacial event is a general glacial excursion, termed a "glacial." Glacials are separated by "interglacials". During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials".

These events are defined differently in different regions of the glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondence between glacials in different regions.

Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another.


click to enlarge



ADDITIONAL REFERENCES






Pleistocene

Pleistocene
2.58 – 0.0117 Ma 
Global sea levels during the last Ice Age.jpg
Map of the world during the Last Glacial Maximum
Chronology
Etymology
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Definition
Chronological unitEpoch
Stratigraphic unitSeries
Time span formalityFormal
Lower boundary definition
Lower boundary GSSPMonte San Nicola Section, GelaSicilyItaly
37.1469°N 14.2035°E
Lower GSSP ratified2009 (as base of Quaternary and Pleistocene)[3]
Upper boundary definitionEnd of the Younger Dryas stadial
Upper boundary GSSPNGRIP2 ice core, Greenland
75.1000°N 42.3200°W
Upper GSSP ratified2008 (as base of Holocene)[4]

The Pleistocene ( /ˈpls.təsn, -t-/ PLYSE-tə-seen, -⁠toh-,[5] often referred to colloquially as the Ice Age) is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in 2009 by the International Union of Geological Sciences, the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of the period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology. The name is a combination of Ancient Greek πλεῖστοςpleīstos, 'most' and καινόςkainós (latinized as cænus), 'new'.

At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by the Isthmus of Panama, causing a faunal interchange between the two regions and changing ocean circulation patterns, with the onset of glaciation in the Northern Hemisphere occurring around 2.7 million years ago. During the Early Pleistocene (2.58–0.8 Ma), archaic humans of the genus Homo originated in Africa and spread throughout Afro-Eurasia. The end of the Early Pleistocene is marked by the Mid-Pleistocene Transition, with the cyclicity of glacial cycles changing from 41,000-year cycles to asymmetric 100,000-year cycles, making the climate variation more extreme. The Late Pleistocene witnessed the spread of modern humans outside of Africa as well as the extinction of all other human species. Humans also spread to the Australian continent and the Americas for the first time, co-incident with the extinction of most large bodied animals in these regions.

The aridification and cooling trends of the preceding Neogene were continued in the Pleistocene. The climate was strongly variable depending on the glacial cycle, with the sea levels being up to 120 metres lower than present at peak glaciation, allowing the connection of Asia and North America via Beringia and the covering of most of northern North America by the Laurentide Ice Sheet.

Etymology

Evolution of temperature in the Post-Glacial period at the very end of the Pleistocene, according to Greenland ice cores[6]
Temperature rise marking the end of the Pleistocene, as derived from Antarctic ice core data.

Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today. This distinguished it from the older Pliocene Epoch, which Lyell had originally thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" ("most new" or "newest") from the Greek πλεῖστος (pleīstos, "most") and καινός (kainós (latinized as cænus), "new");[7][8][9] this contrasts with the immediately preceding Pliocene ("newer", from πλείων (pleíōn, "more") and kainós) and the immediately subsequent Holocene ("wholly new" or "entirely new", from ὅλος (hólos, "whole") and kainósepoch, which extends to the present time.

Dating

The Pleistocene has been dated from 2.580 million (±0.005) to 11,650 years BP[10] with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP.[11] It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell. The end of the Younger Dryas has been dated to about 9640 BC (11,654 calendar years BP). The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not significantly different from previous interglacial intervals within the Pleistocene.[12] In the ICS timescale, the Pleistocene is divided into four stages or ages, the GelasianCalabrianChibanian (previously the unofficial "Middle Pleistocene"), and Upper Pleistocene (unofficially the "Tarantian").[13][14][note 1] In addition to these international subdivisions, various regional subdivisions are often used.

In 2009 the International Union of Geological Sciences (IUGS) confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, and accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.[16] The start date has now been rounded down to 2.580 million years BP.[10] The IUGS has yet to approve a type sectionGlobal Boundary Stratotype Section and Point (GSSP), for the upper Pleistocene/Holocene boundary (i.e. the upper boundary). The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W.[17] The lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossilsDiscoaster pentaradiatus and Discoaster surculus.[18][19] The Pleistocene covers the recent period of repeated glaciations.

The name Plio-Pleistocene has, in the past, been used to mean the last ice age. Formerly, the boundary between the two epochs was drawn at the time when the foraminiferal species Hyalinea baltica first appeared in the marine section at La Castella, Calabria, Italy;[20] however, the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene.

Radiocarbon dating is considered to be inaccurate beyond around 50,000 years ago. Marine isotope stages (MIS) derived from Oxygen isotopes are often used for giving approximate dates.

Deposits

Pleistocene non-marine sediments are found primarily in fluvial deposits, lakebeds, slope and loess deposits as well as in the large amounts of material moved about by glaciers. Less common are cave deposits, travertines and volcanic deposits (lavas, ashes). Pleistocene marine deposits are found primarily in shallow marine basins mostly (but with important exceptions) in areas within a few tens of kilometres of the modern shoreline. In a few geologically active areas such as the Southern California coast, Pleistocene marine deposits may be found at elevations of several hundred metres.

Paleogeography and climate

The maximum extent of glacial ice in the north polar area during the Pleistocene Period

The modern continents were essentially at their present positions during the Pleistocene, the plates upon which they sit probably having moved no more than 100 km (62 mi) relative to each other since the beginning of the period. In glacial periods, the sea level would drop by over 100 m (330 ft) during peak glaciation, exposing large areas of present continental shelf as dry land.

According to Mark Lynas (through collected data), the Pleistocene's overall climate could be characterised as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, and other El Niño markers.[21]

Glacial features[edit]

Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places. It is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, and several hundred in Eurasia. The mean annual temperature at the edge of the ice was −6 °C (21 °F); at the edge of the permafrost, 0 °C (32 °F).

Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres (4,900–9,800 ft) thick, resulting in temporary sea-level drops of 100 metres (300 ft) or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.

The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Zealand and Tasmania. The current decaying glaciers of Mount KenyaMount Kilimanjaro, and the Ruwenzori Range in east and central Africa were larger. Glaciers existed in the mountains of Ethiopia and to the west in the Atlas mountains.

In the northern hemisphere, many glaciers fused into one. The Cordilleran Ice Sheet covered the North American northwest; the east was covered by the Laurentide. The Fenno-Scandian ice sheet rested on northern Europe, including much of Great Britain; the Alpine ice sheet on the Alps. Scattered domes stretched across Siberia and the Arctic shelf. The northern seas were ice-covered.

South of the ice sheets large lakes accumulated because outlets were blocked and the cooler air slowed evaporation. When the Laurentide Ice Sheet retreated, north-central North America was totally covered by Lake Agassiz. Over a hundred basins, now dry or nearly so, were overflowing in the North American west. Lake Bonneville, for example, stood where Great Salt Lake now does. In Eurasia, large lakes developed as a result of the runoff from the glaciers. Rivers were larger, had a more copious flow, and were braided. African lakes were fuller, apparently from decreased evaporation. Deserts, on the other hand, were drier and more extensive. Rainfall was lower because of the decreases in oceanic and other evaporation.

It has been estimated that during the Pleistocene, the East Antarctic Ice Sheet thinned by at least 500 meters, and that thinning since the Last Glacial Maximum is less than 50 meters and probably started after ca 14 ka.[22]

Major events

Ice ages as reflected in atmospheric CO2, stored in bubbles from glacial ice of Antarctica

During the 2.5 million years of the Pleistocene, numerous cold phases called glacials (Quaternary ice age), or significant advances of continental ice sheets, in Europe and North America, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years. The last cold episode of the last glacial period ended about 10,000 years ago.[23] Over 11 major glacial events have been identified, as well as many minor glacial events.[24] A major glacial event is a general glacial excursion, termed a "glacial." Glacials are separated by "interglacials". During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials".

These events are defined differently in different regions of the glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondence between glacials in different regions. Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another.

For most of the 20th century only a few regions had been studied and the names were relatively few. Today the geologists of different nations are taking more of an interest in Pleistocene glaciology. As a consequence, the number of names is expanding rapidly and will continue to expand. Many of the advances and stadials remain unnamed. Also, the terrestrial evidence for some of them has been erased or obscured by larger ones, but evidence remains from the study of cyclical climate changes.

The glacials in the following tables show historical usages, are a simplification of a much more complex cycle of variation in climate and terrain, and are generally no longer used. These names have been abandoned in favour of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognised since the historical terminology was established.[24][25][26]

Historical names of the "four major" glacials in four regions.
RegionGlacial 1Glacial 2Glacial 3Glacial 4
AlpsGünzMindelRissWürm
North EuropeEburonianElsterianSaalianWeichselian
British IslesBeestonianAnglianWolstonianDevensian
Midwest U.S.NebraskanKansanIllinoianWisconsinan
Historical names of interglacials.
RegionInterglacial 1Interglacial 2Interglacial 3
AlpsGünz-MindelMindel-RissRiss-Würm
North EuropeWaalianHolsteinianEemian
British IslesCromerianHoxnianIpswichian
Midwest U.S.AftonianYarmouthianSangamonian

Corresponding to the terms glacial and interglacial, the terms pluvial and interpluvial are in use (Latin: pluvia, rain). A pluvial is a warmer period of increased rainfall; an interpluvial, of decreased rainfall. Formerly a pluvial was thought to correspond to a glacial in regions not iced, and in some cases it does. Rainfall is cyclical also. Pluvials and interpluvials are widespread.

There is no systematic correspondence of pluvials to glacials, however. Moreover, regional pluvials do not correspond to each other globally. For example, some have used the term "Riss pluvial" in Egyptian contexts. Any coincidence is an accident of regional factors. Only a few of the names for pluvials in restricted regions have been stratigraphically defined.

Palaeocycles

The sum of transient factors acting at the Earth's surface is cyclical: climate, ocean currents and other movements, wind currents, temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glaciations of the Pleistocene were caused by the same factors.

The Mid-Pleistocene Transition, approximately one million years ago, saw a change from low-amplitude glacial cycles with a dominant periodicity of 41,000 years to asymmetric high-amplitude cycles dominated by a periodicity of 100,000 years.[27]

However, a 2020 study concluded that ice age terminations might have been influenced by obliquity since the Mid-Pleistocene Transition, which caused stronger summers in the Northern Hemisphere.[28]

Milankovitch cycles

Glaciation in the Pleistocene was a series of glacials and interglacials, stadials and interstadials, mirroring periodic changes in climate. The main factor at work in climate cycling is now believed to be Milankovitch cycles. These are periodic variations in regional and planetary solar radiation reaching the Earth caused by several repeating changes in the Earth's motion.

Milankovitch cycles cannot be the sole factor responsible for the variations in climate since they explain neither the long term cooling trend over the Plio-Pleistocene, nor the millennial variations in the Greenland Ice Cores. Milankovitch pacing seems to best explain glaciation events with periodicity of 100,000, 40,000, and 20,000 years. Such a pattern seems to fit the information on climate change found in oxygen isotope cores.

Oxygen isotope ratio cycles

In oxygen isotope ratio analysis, variations in the ratio of 18
O
 to 16
O
 (two isotopes of oxygen) by mass (measured by a mass spectrometer) present in the calcite of oceanic core samples is used as a diagnostic of ancient ocean temperature change and therefore of climate change. Cold oceans are richer in 18
O
, which is included in the tests of the microorganisms (foraminifera) contributing the calcite.

A more recent version of the sampling process makes use of modern glacial ice cores. Although less rich in 18
O
 than sea water, the snow that fell on the glacier year by year nevertheless contained 18
O
 and 16
O
 in a ratio that depended on the mean annual temperature.

Temperature and climate change are cyclical when plotted on a graph of temperature versus time. Temperature coordinates are given in the form of a deviation from today's annual mean temperature, taken as zero. This sort of graph is based on another of isotope ratio versus time. Ratios are converted to a percentage difference from the ratio found in standard mean ocean water (SMOW).

The graph in either form appears as a waveform with overtones. One half of a period is a Marine isotopic stage (MIS). It indicates a glacial (below zero) or an interglacial (above zero). Overtones are stadials or interstadials.

According to this evidence, Earth experienced 102 MIS stages beginning at about 2.588 Ma BP in the Early Pleistocene Gelasian. Early Pleistocene stages were shallow and frequent. The latest were the most intense and most widely spaced.

By convention, stages are numbered from the Holocene, which is MIS1. Glacials receive an even number; interglacials, odd. The first major glacial was MIS2-4 at about 85–11 ka BP. The largest glacials were 2, 6, 12, and 16; the warmest interglacials, 1, 5, 9 and 11. For matching of MIS numbers to named stages, see under the articles for those names.

Fauna

Both marine and continental faunas were essentially modern but with many more large land mammals such as MammothsMastodonsDiprotodonSmilodontigerlionAurochsshort-faced bearsgiant slothsGigantopithecus and others. Isolated landmasses such as AustraliaMadagascarNew Zealand and islands in the Pacific saw the evolution of large birds and even reptiles such as the Elephant birdmoaHaast's eagleQuinkanaMegalania and Meiolania.

The severe climatic changes during the Ice Age had major impacts on the fauna and flora. With each advance of the ice, large areas of the continents became totally depopulated, and plants and animals retreating southwards in front of the advancing glacier faced tremendous stress. The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply. A major extinction event of large mammals (megafauna), which included mammothsmastodonssaber-toothed catsglyptodons, the woolly rhinoceros, various giraffids, such as the Sivatheriumground slothsIrish elkcave bearsGomphotheresdire wolves, and short-faced bears, began late in the Pleistocene and continued into the Holocene. Neanderthals also became extinct during this period. At the end of the last ice age, cold-blooded animals, smaller mammals like wood mice, migratory birds, and swifter animals like whitetail deer had replaced the megafauna and migrated north. Late Pleistocene bighorn sheep were more slender and had longer legs than their descendants today. Scientists believe that the change in predator fauna after the late Pleistocene extinctions resulted in a change of body shape as the species adapted for increased power rather than speed.[29]

The extinctions hardly affected Africa but were especially severe in North America where native horses and camels were wiped out.

Various schemes for subdividing the Pleistocene

In July 2018, a team of Russian scientists in collaboration with Princeton University announced that they had brought two female nematodes frozen in permafrost, from around 42,000 years ago, back to life. The two nematodes, at the time, were the oldest confirmed living animals on the planet.[30][31]

Humans

The evolution of anatomically modern humans took place during the Pleistocene.[32][33] In the beginning of the Pleistocene Paranthropus species were still present, as well as early human ancestors, but during the lower Palaeolithic they disappeared, and the only hominin species found in fossilic records is Homo erectus for much of the Pleistocene. Acheulean lithics appear along with Homo erectus, some 1.8 million years ago, replacing the more primitive Oldowan industry used by A. garhi and by the earliest species of Homo. The Middle Paleolithic saw more varied speciation within Homo, including the appearance of Homo sapiens about 300,000 years ago.[34]

According to mitochondrial timing techniques, modern humans migrated from Africa after the Riss glaciation in the Middle Palaeolithic during the Eemian Stage, spreading all over the ice-free world during the late Pleistocene.[35][36][37] A 2005 study posits that humans in this migration interbred with archaic human forms already outside of Africa by the late Pleistocene, incorporating archaic human genetic material into the modern human gene pool.[38]


Hominin species during Pleistocene
Homo (genus)AustralopithecusAustralopithecus sedibaAustralopithecus africanusHomo floresiensisHomo neanderthalensisHomo sapiensHomo heidelbergensisHomo erectusHomo nalediHomo habilisHolocenePleistocenePliocene


See also

Explanatory notes

  1. ^ The Upper Pleistocene is a subseries/subepoch rather than a stage/age but, in 2009, the IUGS decided that it will be replaced with a stage/age (currently unofficially/informally named the Tarantian).[15]

References

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External links