intellectual vanities… about close to everything

Archive for the ‘World History’ Category

What can we learn from disease stigma’s long history?

leave a comment »

What can we learn from disease stigma’s long history?.

Advertisements

Written by huehueteotl

November 27, 2012 at 11:13 pm

On the Dark Side in Al Doura – A Soldier in the Shadow

leave a comment »

If any a story of PTSD was tragic, this one is: “U.S. Army Ranger John Needham, who was awarded two purple hearts and three medals for heroism, wrote to military authorities in 2007 reporting war crimes that he witnessed being committed by his own command and fellow soldiers in Al Doura, Iraq. His charges were supported by atrocity photos which, in the public interest, are now released in this video. John paid a terrible price for his opposition to these acts. His story is tragic. ” Credits to Cindy Piester
work4peacenow@gmail.com

Written by huehueteotl

January 9, 2012 at 10:21 pm

Linguistic Niche Hypothesis – Language Structure Partly Determined by Social Structure

with one comment

Psychologists at the University of Pennsylvania and the University of Memphis have released a new study on linguistic evolution that challenges the prominent hypothesis for why languages differ throughout the world.

Geographic distribution of the 2,236 languages included in the present study.

The study argues that human languages may adapt more like biological organisms than previously thought and that the more common and popular the language, the simpler its construction to facilitate its survival.

Traditional thinking is that languages develop based upon random change and historical drift. For example, English and Turkish are very different languages based upon histories that separate them in space and time. For years, it has been the reigning assumption in the linguistic sciences.

The recent report, published in the current issue of PLoS One, offers a new hypothesis, challenging the drift explanation. Gary Lupyan, a postdoctoral researcher in the Department of Psychology in Penn’s School of Arts and Sciences, and Rick Dale, an assistant professor in psychology at the University of Memphis, conducted a large-scale statistical analysis of more than 2,000 of the world’s languages aimed at testing whether certain social environments are correlated with certain linguistic properties.

The researchers found striking relationships between the demographic properties of a language — such as its population and global spread — and the grammatical complexity of those languages. Languages having the most speakers — and those that have spread around the world — were found to have far simpler grammars, specifically morphology, than languages spoken by few people and in circumscribed regions. For example, languages spoken by more than 100,000 people are almost six times more likely to have simple verb conjugations compared to languages spoken by fewer than 100,000 people.

Larger populations tend to have simpler pronoun and number systems and a smaller number of cases and genders and in general do not employ complex prefixing or suffixing rules in their grammars. A consequence is that languages with long histories of adult learners have become easier to learn over time. Although a number of researchers have predicted such relationships between social and language structure, this is the first large-scale statistical test of this idea.

The results draw connections between the evolution of human language and biological organisms. Just as very distantly related organisms converge on evolutionary strategies in particular niches, languages may adapt to the social environments in which they are learned and used.

“English, for all its confusing spelling and exceptions — if a baker bakes, what does a grocer do? — has a relatively simple grammar,” Lupyan said. “Verbs are easy to conjugate and nouns are mostly pluralized by adding ‘s.’ In comparison, a West African language like Hausa has dozens of ways to make nouns plural and in many languages — Turkish, Aymara, Ladakhi, Ainu — verbs like ‘to know’ have to include information about the origin of the speaker’s knowledge. This information is often conveyed using complex rules, which the most widely-spoken languages on earth like English and Mandarin lack.”

Lupyan and Dale call this social affect on grammatical patterns the “Linguistic Niche Hypothesis.” Languages evolve within particular socio-demographic niches. Although all languages must be learnable by infants, the introduction of adult learners to some languages (for example, through migration or colonization) means that aspects of a language difficult for adults to learn will be less likely to be passed on to subsequent generations of learners. The result is that languages spoken by more people over larger geographic regions have become morphologically simpler over many generations.

A remaining puzzle is why languages with few speakers are so complex in the first place. One possibility, explored by researchers, is that features such as grammatical gender and complex conjugational systems, while difficult for adult learners to master, may facilitate language learning in children by providing a network of redundant information that can cue children in on the meanings of words and how to string them together.

The results and theory proposed by Lupyan and Dale do not aim to explain why a specific language has the grammar it does. Because the findings are statistical in nature, many exceptions to Lupyan and Dale’s theory can be identified. Their work, however, provides a comprehensive analysis of how some social factors influence the structure of language and shows that the relationships between language and culture is far from arbitrary.

The study was funded by an Integrative Graduate Education and Research Training award to the Institute for Research in Cognitive Science at Penn and by the National Science Foundation.

PLoS ONE, 2010; 5 (1): e8559 DOI: 10.1371/journal.pone.0008559
Language Structure Is Partly Determined by Social Structure
Gary Lupyan1*, Rick Dale2

1 Institute for Research on Cognitive Science and Center for Cognitive Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America,
2 Department of Psychology, The University of Memphis, Memphis, Tennessee, United States of America

Abstract
Background: Languages differ greatly both in their syntactic and morphological systems and in the social environments in which they exist. We challenge the view that language grammars are unrelated to social environments in which they are learned and used. Methodology/Principal Findings We conducted a statistical analysis of >2,000 languages using a combination of demographic sources and the World Atlas of Language Structures— a database of structural language properties. We found strong relationships between linguistic factors related to morphological complexity, and demographic/socio-historical factors such as the number of language users, geographic spread, and degree of language contact. The analyses suggest that languages spoken by large groups have simpler inflectional morphology than languages spoken by smaller groups as measured on a variety of factors such as case systems and complexity of conjugations. Additionally, languages spoken by large groups are much more likely to use lexical strategies in place of inflectional morphology to encode evidentiality, negation, aspect, and possession. Our findings indicate that just as biological organisms are shaped by ecological niches, language structures appear to adapt to the environment (niche) in which they are being learned and used. As adults learn a language, features that are difficult for them to acquire, are less likely to be passed on to subsequent learners. Languages used for communication in large groups that include adult learners appear to have been subjected to such selection. Conversely, the morphological complexity common to languages used in small groups increases redundancy which may facilitate language learning by infants. Conclusions/Significance We hypothesize that language structures are subjected to different evolutionary pressures in different social environments. Just as biological organisms are shaped by ecological niches, language structures appear to adapt to the environment (niche) in which they are being learned and used. The proposed Linguistic Niche Hypothesis has implications for answering the broad question of why languages differ in the way
they do and makes empirical predictions regarding language acquisition capacities of children versus adults.

Written by huehueteotl

January 22, 2010 at 8:48 am

Posted in World History

Boots No. 1 Dating Back To Cleopatra?

leave a comment »

 Marketers and critics alike have assumed that branding began in the West with the Industrial Revolution. But a pioneering new study in the February 2008 issue of Current Anthropology finds that attachment to brands far predates modern capitalism, and indeed modern Western society.  Hence author David Wengrow explains: “… combined use of seals and standardized packaging played a central role in the emergence of the world’s first large-scale economies. Comparative analysis of more recent branding practices suggests that these functions may necessarily be intertwined, since the enchanting properties of branded commodities are grounded in guarantees of quality, which in turn are based—paradoxically—upon the disenchantment of production.”
He thus challenges the widespread assumption that branding did not become an important force in social and economic life until the Industrial Revolution. Wengrow presents compelling evidence that labels on ancient containers, which have long been assumed to be simple identifiers, as well as practices surrounding the production and distribution of commodities, actually functioned as branding strategies. Furthermore, these strategies have deep cultural origins and cognitive foundations, beginning in the civilizations of Egypt and Iraq thousands of years ago.

https://i1.wp.com/cuneiform.ucla.edu/wiki/images/thumb/b/b3/300px-Lateuruk04_tn.jpg

Branding became necessary when large-scale economies started mass-producing commodities such as alcoholic drinks, cosmetics and textiles. Ancient societies not only imposed strict forms of quality control over these commodities, but as today they needed to convey value to the consumer. Wengrow finds that commodities in any complex, large society needs to pass through a “nexus of authenticity.”

Through history, these have taken the form of “the bodies of the ancestral dead, the gods, heads of state, secular business gurus, media celebrities, or that core fetish of post-modernity, the body of the sovereign consumer citizen in the act of self-fashioning.” Although capitalism and branding find in each other a perfect complement, they have distinct origins. Wengrow shows that branding has for millennia filled a deep-seated need for us humans to find value in the goods that we consume.

Egyptian perfume bottle. Could product branding have begun in ancient Egypt? (Credit: iStockphoto)
Current Anthropology Volume 49, Number 1, February 2008 © 2008 by The Wenner-Gren Foundation for Anthropological Research. All rights reserved.0011-3204/2008/4901-0001 DOI: 10.1086/523676

Prehistories of Commodity Branding

by David Wengrow

Commodity branding has been characterized as the distinguishing cultural move of late capitalism and is widely viewed as a historically distinctive feature of the modern global economy. The brand’s rise to prominence following the Industrial Revolution and the attendant shift of corporate enterprise towards the dissemination of image-based products have been further cited as contributing to the erosion of older forms of identity such as those based on kinship and class. However, comparisons between recent forms of branding and much earlier modes of commodity marking associated with the Urban Revolution of the fourth millennium BC suggest that systems of branding address a paradox common to all economies of scale and are therefore likely to arise (and to have arisen) under a wide range of ideological and institutional conditions, including those of sacred hierarchies and stratified states. An examination of the material and cognitive properties of sealing practices and the changing functions of seals in their transition from personal amulets to a means of labeling mass-produced goods helps to unpack the interlocking (pre)histories of quality control, authenticity, and ownership that make up the modern brand.

Written by huehueteotl

February 20, 2008 at 3:47 pm

Languages Evolve In Rapid Bursts

with one comment

Scientists at the University of Reading have discovered that languages change and evolve in rapid bursts rather than in a steady pattern. The research investigates thousands of years of language evolution, and looks at the way in which languages split and evolve. It has long been accepted that the desire for a distinct social identity may cause languages to change quickly, but it has not previously been known whether such rapid bursts of change are a regular feature of the evolution of human language.

The findings show that initially, the basic vocabulary of newly formed languages develops and changes quite quickly, and this is then followed by longer periods of slower and gradual change.

Rapid bursts of change at the time of language splitting are important processes in language evolution, and the research has found that these account for between 10 and 33 % of the total divergence amongst the basic vocabularies of the language groups studied. The research used data to construct evolutionary tree diagrams to explore the relationships between languages. The diagrams describe the separate paths of evolution leading from a common ancestral language to a set of distinct languages at the tips of the tree.

Professor Mark Pagel from the University of Reading said “Our research suggests that rapid bursts of change occur in languages, and this reflects a human ability to adjust languages at critical times of cultural evolution, such as during the emergence of new and rival groups.

The emergence of American English took place when the American English Dictionary was introduced by Noah Webster. He insisted that ‘as an independent nation, our honor requires us to have a system of our own, in language as well as Government’. This illustrates that language is not only used as a means of communication, but it is also important for social functions, including promoting group identity and unity.”
Science 1 February 2008: 588 DOI: 10.1126/science.1149683
Languages Evolve in Punctuational Bursts
Quentin D. Atkinson,1* Andrew Meade,1 Chris Venditti,1 Simon J. Greenhill,2 Mark Pagel1,3{dagger}

Linguists speculate that human languages often evolve in rapid or punctuational bursts, sometimes associated with their emergence from other languages, but this phenomenon has never been demonstrated. We used vocabulary data from three of the world’s major language groups—Bantu, Indo-European, and Austronesian—to show that 10 to 33% of the overall vocabulary differences among these languages arose from rapid bursts of change associated with language-splitting events. Our findings identify a general tendency for increased rates of linguistic evolution in fledgling languages, perhaps arising from a linguistic founder effect or a desire to establish a distinct social identity.

1 School of Biological Sciences, University of Reading, Reading RG6 6AS, UK.
2 Department of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
3 Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA.

* Present address: Institute of Cognitive and Evolutionary Anthropology, University of Oxford, Oxford OX2 6QS, UK.

{dagger} To whom correspondence should be addressed. E-mail: m.pagel@reading.ac.uk

Written by huehueteotl

February 7, 2008 at 4:42 pm

Humans Evolving Faster – And We Are Becoming More Different, Not Alike

with 4 comments

Researchers have discovered genetic evidence that human evolution is speeding up — and has not halted or proceeded at a constant rate, as had been thought — indicating that humans on different continents are becoming increasingly different.

“We aren’t the same as people even 1,000 or 2,000 years ago,” says University of Utah anthropologist Henry Harpending. That might explain, for example, part of the difference between Viking invaders and their peaceful Swedish descendants. (Credit: iStockphoto/Manuel Velasco)

“We used a new genomic technology to show that humans are evolving rapidly, and that the pace of change has accelerated a lot in the last 40,000 years, especially since the end of the Ice Age roughly 10,000 years ago,” says research team leader Henry Harpending, a distinguished professor of anthropology at the University of Utah.

Harpending says there are provocative implications from the study, published online Monday, Dec. 10 in the journal Proceedings of the National Academy of Sciences:

— “We aren’t the same as people even 1,000 or 2,000 years ago,” he says, which may explain, for example, part of the difference between Viking invaders and their peaceful Swedish descendants. “The dogma has been these are cultural fluctuations, but almost any temperament trait you look at is under strong genetic influence.”

— “Human races are evolving away from each other,” Harpending says. “Genes are evolving fast in Europe, Asia and Africa, but almost all of these are unique to their continent of origin. We are getting less alike, not merging into a single, mixed humanity.” He says that is happening because humans dispersed from Africa to other regions 40,000 years ago, “and there has not been much flow of genes between the regions since then.”

“Our study denies the widely held assumption or belief that modern humans [those who widely adopted advanced tools and art] appeared 40,000 years ago, have not changed since and that we are all pretty much the same. We show that humans are changing relatively rapidly on a scale of centuries to millennia, and that these changes are different in different continental groups.”

The increase in human population from millions to billions in the last 10,000 years accelerated the rate of evolution because “we were in new environments to which we needed to adapt,” Harpending adds. “And with a larger population, more mutations occurred.”

Study co-author Gregory M. Cochran says: “History looks more and more like a science fiction novel in which mutants repeatedly arose and displaced normal humans — sometimes quietly, by surviving starvation and disease better, sometimes as a conquering horde. And we are those mutants.”

Harpending conducted the study with Cochran, a New Mexico physicist, self-taught evolutionary biologist and adjunct professor of anthropology at the University of Utah; anthropologist John Hawks, a former Utah postdoctoral researcher now at the University of Wisconsin, Madison; geneticist Eric Wang of Affymetrix, Inc. in Santa Clara, Calif.; and biochemist Robert Moyzis of the University of California, Irvine.

No Justification for Discrimination

The new study comes from two of the same University of Utah scientists — Harpending and Cochran — who created a stir in 2005 when they published a study arguing that above-average intelligence in Ashkenazi Jews — those of northern European heritage — resulted from natural selection in medieval Europe, where they were pressured into jobs as financiers, traders, managers and tax collectors. Those who were smarter succeeded, grew wealthy and had bigger families to pass on their genes. Yet that intelligence also is linked to genetic diseases such as Tay-Sachs and Gaucher in Jews.

That study and others dealing with genetic differences among humans — whose DNA is more than 99 percent identical — generated fears such research will undermine the principle of human equality and justify racism and discrimination. Other critics question the quality of the science and argue culture plays a bigger role than genetics.

Harpending says genetic differences among different human populations “cannot be used to justify discrimination. Rights in the Constitution aren’t predicated on utter equality. People have rights and should have opportunities whatever their group.”

Analyzing SNPs of Evolutionary Acceleration

The study looked for genetic evidence of natural selection — the evolution of favorable gene mutations — during the past 80,000 years by analyzing DNA from 270 individuals in the International HapMap Project, an effort to identify variations in human genes that cause disease and can serve as targets for new medicines.

The new study looked specifically at genetic variations called “single nucleotide polymorphisms,” or SNPs (pronounced “snips”) which are single-point mutations in chromosomes that are spreading through a significant proportion of the population.

Imagine walking along two chromosomes — the same chromosome from two different people. Chromosomes are made of DNA, a twisting, ladder-like structure in which each rung is made of a “base pair” of amino acids, either G-C or A-T. Harpending says that about every 1,000 base pairs, there will be a difference between the two chromosomes. That is known as a SNP.

Data examined in the study included 3.9 million SNPs from the 270 people in four populations: Han Chinese, Japanese, Africa’s Yoruba tribe and northern Europeans, represented largely by data from Utah Mormons, says Harpending.

Over time, chromosomes randomly break and recombine to create new versions or variants of the chromosome. “If a favorable mutation appears, then the number of copies of that chromosome will increase rapidly” in the population because people with the mutation are more likely to survive and reproduce, Harpending says.

“And if it increases rapidly, it becomes common in the population in a short time,” he adds.

The researchers took advantage of that to determine if genes on chromosomes had evolved recently. Humans have 23 pairs of chromosomes, with each parent providing one copy of each of the 23. If the same chromosome from numerous people has a segment with an identical pattern of SNPs, that indicates that segment of the chromosome has not broken up and recombined recently.

That means a gene on that segment of chromosome must have evolved recently and fast; if it had evolved long ago, the chromosome would have broken and recombined.

Harpending and colleagues used a computer to scan the data for chromosome segments that had identical SNP patterns and thus had not broken and recombined, meaning they evolved recently. They also calculated how recently the genes evolved.

A key finding: 7 percent of human genes are undergoing rapid, recent evolution.

The researchers built a case that human evolution has accelerated by comparing genetic data with what the data should look like if human evolution had been constant:

  • The study found much more genetic diversity in the SNPs than would be expected if human evolution had remained constant.
  • If the rate at which new genes evolve in Africans was extrapolated back to 6 million years ago when humans and chimpanzees diverged, the genetic difference between modern chimps and humans would be 160 times greater than it really is. So the evolution rate of Africans represents a recent speedup in evolution.
  • If evolution had been fast and constant for a long time, there should be many recently evolved genes that have spread to everyone. Yet, the study revealed many genes still becoming more frequent in the population, indicating a recent evolutionary speedup.

Next, the researchers examined the history of human population size on each continent. They found that mutation patterns seen in the genome data were consistent with the hypothesis that evolution is faster in larger populations.

Evolutionary Change and Human History: Got Milk?

“Rapid population growth has been coupled with vast changes in cultures and ecology, creating new opportunities for adaptation,” the study says. “The past 10,000 years have seen rapid skeletal and dental evolution in human populations, as well as the appearance of many new genetic responses to diet and disease.”

The researchers note that human migrations into new Eurasian environments created selective pressures favoring less skin pigmentation (so more sunlight could be absorbed by skin to make vitamin D), adaptation to cold weather and dietary changes.

Because human population grew from several million at the end of the Ice Age to 6 billion now, more favored new genes have emerged and evolution has speeded up, both globally and among continental groups of people, Harpending says.

“We have to understand genetic change in order to understand history,” he adds.

For example, in China and most of Africa, few people can digest fresh milk into adulthood. Yet in Sweden and Denmark, the gene that makes the milk-digesting enzyme lactase remains active, so “almost everyone can drink fresh milk,” explaining why dairying is more common in Europe than in the Mediterranean and Africa, Harpending says.

He now is studying if the mutation that allowed lactose tolerance spurred some of history’s great population expansions, including when speakers of Indo-European languages settled all the way from northwest India and central Asia through Persia and across Europe 4,000 to 5,000 years ago. He suspects milk drinking gave lactose-tolerant Indo-European speakers more energy, allowing them to conquer a large area.

But Harpending believes the speedup in human evolution “is a temporary state of affairs because of our new environments since the dispersal of modern humans 40,000 years ago and especially since the invention of agriculture 12,000 years ago. That changed our diet and changed our social systems. If you suddenly take hunter-gatherers and give them a diet of corn, they frequently get diabetes. We’re still adapting to that. Several new genes we see spreading through the population are involved with helping us prosper with high-carbohydrate diet.”

PNAS | January 8, 2002 | vol. 99 | no. 1 | 10-12

Commentary
In our genes

Henry Harpending*,dagger and Gregory CochranDagger dagger Department of Anthropology, University of Utah, Salt Lake City, UT 84112; and Dagger Reconstruction Concepts, 6708 Loftus Northeast, Albuquerque, NM 87109

The D4 dopamine receptor (DRD4) locus may be a model system for understanding the relationship between genetic variation and human cultural diversity. It has been the subject of intense interest in psychiatry, because bearers of one variant are at increased risk for attention deficit hyperactivity disorder (ADHD) (1). A survey of world frequencies of DRD4 alleles has shown striking differences among populations (2), with population differences greater than those of most neutral markers. In this issue of PNAS Ding et al. (3) provide a detailed molecular portrait of world diversity at the DRD4 locus. They show that the allele associated with ADHD has increased a lot in frequency within the last few thousands to tens of thousands of years, although it has probably been present in our ancestors for hundreds of thousands or even millions of years. There is a repeat polymorphism in exon III of the gene at which a variable number of 48-bp motifs can occur. The common and probable ancestral allele has four repeats (4R), whereas the allele associated with novelty seeking and ADHD has seven (7R). Ding et al. (3) show that there are essentially two allele classes at the locus: most variants are easily derived from 4R by simple recombinations or mutations, whereas 7R differs from 4R by a minimum of seven events. This means either that the coalescence of the 4R and 7R allele classes is ancient or that 7R was generated by an extremely improbable mutation and recombination event more recently. At any rate the allelic diversity within the 4R class and the lack of linkage disequilibrium with markers around it show that it has been the common variant in our species for a long time. 7R alleles, with little diversity within the class and . . . [Full Text of this Article]

see also:

Evidence of positive selection acting at the human dopamine receptor D4 gene locus
Yuan-Chun Ding, Han-Chang Chi, Deborah L. Grady, Atsuyuki Morishima, Judith R. Kidd, Kenneth K. Kidd, Pamela Flodman, M. Anne Spence, Sabrina Schuck, James M. Swanson, Ya-Ping Zhang, and Robert K. Moyzis
PNAS 2002 99: 309-314. [Abstract] [Full Text]

Age-old Mystery Of Missing Chemicals From Earth’s Mantle May Be Solved

leave a comment »

Observations about the early formation of Earth may answer an age-old question about why the planet’s mantle is missing some of the matter that should be present, according to UBC geophysicist John Hernlund.

Earth is made from chondrite, very primitive rocks of meteorites that date from the earliest time of the solar system before the Earth was formed. However, scientists have been puzzled why the composition of Earth’s mantle and core differed from that of chondrite.

Hernlund’s findings suggest that an ancient magma ocean swirled beneath the Earth’s surface and would account for the discrepancy.

Over its 4.5 billion history, Earth’s layers of molten rock evolved and crystallized, cooling from a magma ocean (yellow) to the mantle (grey) around the planet’s core (orange). (Credit: Image courtesy of University of British Columbia)

“As the thick melted rock cooled and crystallized, the solids that resulted had a different composition than the melt,” explains Hernlund, a post-doctoral fellow at UBC Earth and Ocean Sciences.

“The melt held onto some of the elements. This would be where the missing elements of chondrite are stored.”

He says this layer of molten rock would have been around 1,000 km thick and 2,900 km beneath the surface.”

Hernlund’s study explores the melting and crystallization processes that have controlled the composition of the Earth’s interior over geological time. Co-authors are Stéphane Labrosse, Ecole Normale Superieure de Lyon and Nicolas Coltice, Université de Lyon.

The centre of Earth is a fiery core of melted heavy metals, mostly iron. This represents 30 per cent while the remaining 70 per cent is the outer mantle of solid rock.

Traditional views hold that a shallow ocean of melted rock (magma) existed 1,000 km below the Earth’s surface, but it was short lived and gone by 10 million years after the formation of Earth.

In contrast, Hernlund’s evolutionary model predicts that during Earth’s hotter past shortly after its formation 4.5 billion years ago, at least one-third of the mantle closest to the core was also melted.

The partially molten patches now observed at the base of the Earth’s mantle could be the remnants of such a deep magma ocean, says Hernlund.

Letter

Nature 450, 866-869 (6 December 2007) | doi:10.1038/nature06355; Received 21 May 2007; Accepted 2 October 2007

A crystallizing dense magma ocean at the base of the Earth’s mantle

S. Labrosse1, J. W. Hernlund2,4 & N. Coltice1,3

1. Laboratoire des sciences de la Terre, Ecole Normale Supérieure de Lyon, Université de Lyon, CNRS UMR 5570, 46 Allée d’Italie, 69364 Lyon Cedex 07, France
2. Équipe de Dynamique des Fluides Géologiques, Institut de Physique du Globe de Paris, 4 place Jussieu, 75252 Paris Cedex 05, France
3. Laboratoire des sciences de la Terres, Université Lyon 1, Université de Lyon, CNRS UMR 5570, 2 rue Raphael Dubois, 69622 Villeurbanne Cedex, France
4. Present address: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.

Correspondence to: S. Labrosse1 Correspondence and requests for materials should be addressed to S.L. (Email: stephane.labrosse@ens-lyon.fr).

The distribution of geochemical species in the Earth’s interior is largely controlled by fractional melting and crystallization processes that are intimately linked to the thermal state and evolution of the mantle. The existence of patches of dense partial melt at the base of the Earth’s mantle, together with estimates of melting temperatures for deep mantle phases and the amount of cooling of the underlying core required to maintain a geodynamo throughout much of the Earth’s history, suggest that more extensive deep melting occurred in the past. Here we show that a stable layer of dense melt formed at the base of the mantle early in the Earth’s history would have undergone slow fractional crystallization, and would be an ideal candidate for an unsampled geochemical reservoir hosting a variety of incompatible species (most notably the missing budget of heat-producing elements) for an initial basal magma ocean thickness of about 1,000 km. Differences in 142Nd/144Nd ratios between chondrites and terrestrial rocks can be explained by fractional crystallization with a decay timescale of the order of 1 Gyr. These combined constraints yield thermal evolution models in which radiogenic heat production and latent heat exchange prevent early cooling of the core and possibly delay the onset of the geodynamo to 3.4–4 Gyr ago.