-- Land-ice melt at the end of the last five ice-ages - 9/25/14
-- Cholera is Altering the Human Genome - 7/3/13
|Within ice ages, there exist periods of
more severe glacial conditions and more temperate referred to as glacial
periods and interglacial periods, respectively. The Earth is currently in
an interglacial period of the Quaternary Ice Age, with the last glacial
period of the Quaternary having ended approximately 10,000 years ago with
the start of the Holocene epoch.
Timeline of Known Glaciation
Originally, the glacial and interglacial periods of the Quaternary Ice Age were named after characteristic geological features, and these names varied from region to region. It is now more common for researchers to refer to the periods by their marine isotopic stage number. The marine record preserves all the past glaciations; the land-based evidence is less complete because successive glaciations may wipe out evidence of their predecessors. Ice cores from continental ice accumulations also provide a complete record, but do not go as far back in time as marine data. Pollen data from lakes and bogs as well as loess profiles provided important land-based correlation data. The names system has not been completely filled out since the technical discussion moved to using marine isotopic stage numbers. For example, there are five Pleistocene glacial/interglacial cycles recorded in marine sediments during the last half million years, but only three classic interglacials were originally recognized on land during that period (Mindel, Riss and Würm).
Ice core evidence of recent glaciation
Ice cores are used to obtain a high resolution record of recent glaciation. It confirms the chronology of the marine isotopic stages. Ice core data shows that the last 400,000 years have consisted of short interglacials (10,000 to 30,000 years) about as warm as the present alternated with much longer (70,000 to 90,000 years) glacials substantially colder than present. The new EPICA Antarctic ice core has revealed that between 400,000 and 780,000 years ago, interglacials occupied a considerably larger proportion of each glacial/interglacial cycle, but were not as warm as subsequent interglacials.
sea levels rose at the end of each of the last five ice ages.
September 25, 2014 University of Southampton
Summary: Land-ice melt at the end of the last five ice-ages caused global sea-levels to rise at rates of up to 5.5 metres per century, according to a new study. Researchers developed a 500,000-year record of sea-level variability, to provide the first account of how quickly sea-level changed during the last five ice-age cycles. Scientists also found that more than 100 smaller events of sea-level rise took place in between the five major events.
Land-ice decay at the end of the last five ice-ages caused global sea-levels to rise at rates of up to 5.5 metres per century, according to a new study.
An international team of researchers developed a 500,000-year record of sea-level variability, to provide the first account of how quickly sea-level changed during the last five ice-age cycles.
The results, published in the latest issue of Nature Communications, also found that more than 100 smaller events of sea-level rise took place in between the five major events.
Dr Katharine Grant, from the Australian National University (ANU), Canberra, who led the study, says: "The really fast rates of sea-level rise typically seem to have happened at the end of periods with exceptionally large ice sheets, when there was two or more times more ice on the Earth than today.
"Time periods with less than twice the modern global ice volume show almost no indications of sea-level rise faster than about 2 metres per century. Those with close to the modern amount of ice on Earth, show rates of up to 1 to 1.5 metres per century."
Co-author Professor Eelco Rohling, of both the University of Southampton and ANU, explains that the study also sheds light on the timescales of change.. He says: "For the first time, we have data from a sufficiently large set of events to systematically study the timescale over which ice-sheet responses developed from initial change to maximum retreat."
"This happened within 400 years for 68 per cent of all 120 cases considered, and within 1100 years for 95 per cent. In other words, once triggered, ice-sheet reduction (and therefore sea-level rise) kept accelerating relentlessly over periods of many centuries."
Professor Rohling speculates that there may be an important lesson for our future: "Man-made warming spans 150 years already and studies have documented clear increases in mass-loss from the Antarctic and Greenland ice sheets.. Once under way, this response may be irreversible for many centuries to come."
The team reconstructed sea-levels using data from sediment cores from the Red Sea, an area that is very sensitive to sea-level changes because it's only natural connection with the open (Indian) ocean is through the very shallow (137 metre) Bab-el-Mandab Strait. These sediment samples record wind-blown dust variations, which the team linked to a well-dated climate record from Chinese stalagmites. Due to a common process, both dust and stalagmite records show a pronounced change at the end of each ice age, which allowed the team to date the sea-level record in detail.
The researchers emphasise that their values for sea-level change are 500-year averages, so brief pulses of faster change cannot be excluded.
The study was funded primarily by Natural Environment Research Council (NERC) and the Australian Research Council (ARC).
The above story is based on materials provided by University of Southampton. Note: Materials may be edited for content and length.
Katharine Grant, Eelco Rohling. Sea-level variability over five glacial cycles. Nature Communications, 2014 DOI: 10.1038/ncomm6076
Cite This Page:
University of Southampton. "Global sea levels rose up to five meters per century at the end of the last five ice age." ScienceDaily. ScienceDaily, 25 September 2014. <www.sciencedaily.com/releases/2014/09/140925082223.htm>.
Note: I read elsewhere a report that as ice ages advance and retreated, DNA changed -- perhaps to provide a more probable adaptation to the conditions. It seems that is true for every ice age primates have survived. That is especially evident in mtDNA which can be traced back 100s of thousands of years. There is a however to this age statement -- A trace can only be made back as far as there are progenators who survived throughout time. In the case of homosaphens there was a time when most all of our ancestors were on the verge of extenction, between 70,000 and 80,000 years ago. So in the case of todays mt-mothers the available history was cut short. -- Another however exist, fossels have given up mtDNA which has driven DNA knowledge of our primate ancestors. Much of that information or links is found on this web site (oghgul).
Cholera is Altering
the Human Genome
by Mitch Leslie on 3 July 2013
Dhaka, Bangladesh, a country where nearly half the people are infected with the cholera bacterium by age 15.
Cholera kills thousands of people a year, but a new study suggests that the human body is fighting back. Researchers have found evidence that the genomes of people in Bangladesh—where the disease is prevalent—have developed ways to combat the disease, a dramatic case of human evolution happening in modern times.
Cholera has hitchhiked around the globe, even entering Haiti with UN peacekeepers in 2010, but the disease's heartland is the Ganges River Delta of India and Bangladesh. It has been killing people there for more than a thousand years. By the time they are 15 years old, half of the children in Bangladesh have been infected with the cholera-causing bacterium, which spreads in contaminated water and food. The microbe can cause torrential diarrhea, and, without treatment, "it can kill you in a matter of hours," says Elinor Karlsson, a computational geneticist at Harvard and co-author of the new study.
The fact that cholera has been around so long, and that it kills children—thus altering the gene pool of a population—led the researchers to suspect that it was exerting evolutionary pressure on the people in the region, as malaria has been shown to do in Africa. Another hint that the microbe drives human evolution, notes Regina LaRocque, a study co-author and infectious disease specialist at Massachusetts General Hospital, Boston, is that many people suffer mild symptoms or don't get sick at all, suggesting that they have adaptations to counter the bacterium.
To tease out the disease's evolutionary impact, Karlsson, LaRocque, and their colleagues, including scientists from the International Centre for Diarrhoeal Disease Research in Bangladesh, used a new statistical technique that pinpoints sections of the genome that are under the influence of natural selection. The researchers analyzed DNA from 36 Bangladeshi families and compared it to the genomes of people from northwestern Europe, West Africa, and eastern Asia. Natural selection has left its mark on 305 regions in the genome of the subjects from Bangladesh, the team reveals online today in Science Translational Medicine.
The researchers bolstered the case that cholera was the driving force behind the genomic changes by contrasting DNA from Bangladeshi cholera patients with DNA from other residents of the country who remained healthy despite living in the same house as someone who fell ill with the disease. Individuals who were susceptible to cholera typically carried DNA variants that lie within the region that shows the strongest effect from natural selection.
One category of genes that is evolving in response to cholera, the researchers found, encodes potassium channels that release chloride ions into the intestines. Their involvement makes sense because the toxin spilled by the cholera bacterium spurs such channels to discharge large amounts of chloride, leading to the severe diarrhea that's characteristic of the disease.
A second category of selected genes helps manage the protein NF- kB, the master controller of inflammation, which is one of the body's responses to the cholera bacterium. A third category involves genes that adjust the activity of the inflammasome, a protein aggregation inside our cells that detects pathogens and fires up inflammation. However, the researchers don't know what changes natural selection promotes in these genes to strengthen defenses against the cholera bacterium.
Researchers have identified other examples of infectious diseases driving human evolution, such as malaria in Africa favoring the sickle cell allele, a gene variant that provides resistance to the illness. But they are just starting to search the entire genome for signs of disease effects, and this study is the first to use such methods for cholera.
"I think it's a great example of the impact infectious diseases have had on human evolution," says infectious disease specialist William Petri of the University of Virginia School of Medicine in Charlottesville, who wasn't involved with the study. "It's ambitious, fairly extensive, and very well done," adds medical microbiologist Jan Holmgren of the University of Gothenburg in Sweden. One strength of the work is that it flags genes, such as those involved with the inflammasome, that researchers have implicated in other intestinal illnesses such as inflammatory bowel disease, says genetic epidemiologist Priya Duggal of the Johns Hopkins Center for Global Health in Baltimore, Maryland. "Overall, they make a very nice case."
The findings probably won't lead to new cholera treatments, says LaRocque, because current measures—which rapidly replace the water and electrolytes patients lose—work very well. "The real issue with cholera," she says, "is how do we prevent it," a difficult problem in areas without clean water supplies. But understanding how humans have evolved in response to cholera might help researchers devise more potent vaccines that would provide better protection against this killer, she says.
Credit: Science Magazine Jul 3, 2013
Credit: Mark Knobil/Creative Commons