23 de fevereiro de 2005
Age of ancient humans reassessed
Two skulls originally found in 1967 have been shown to be about 195,000 years old, making them the oldest modern human remains known to science.
The age estimate comes from a re-dating of Ethiopian rock layers close to those that yielded the remarkable fossils.
The skulls, known as Omo I and II, push back the known presence of Homo sapiens in Africa by 40,000 years.
The latest dating work is reported in the science journal Nature.
It puts the specimens close to the time expected for the evolutionary emergence of our species. Genetic studies have indicated Homo sapiens arose in East Africa - possibly Ethiopia or Tanzania - just over 200,000 years ago.
"These are the earliest known examples of our own species and that suggests they lived earlier still," commented Nature senior editor Dr Henry Gee.
"But I am not sure how much further back you could go and still have Homo sapiens - before they graded into some other, earlier species," he told the BBC News website.
Dig return
The skulls were first brought to the attention of the world by the famous fossil hunter Richard Leakey, whose team unearthed the specimens in sediments along the Omo River in southernmost Ethiopia, near the town of Kibish.
They found the skull (minus the face) and partial skeleton (parts of arms, legs, feet and the pelvis) of Omo I, and the top and back of the skull of Omo II.
Now, a three-man Australian-US team - Ian McDougall, Frank Brown and John Fleagle - has re-evaluated the Leakey finds.
The team even returned to the original excavation area, using old scientific reports, photographs and film to identify the precise dig co-ordinates.
"Omo I actually has the better information on it," explained co-author Professor Brown, from the University of Utah's College of Mines and Earth Sciences.
"[The records and maps] are correct and we actually went back and found a few more pieces of the skeleton and some of them glue on to the pieces that were found in 1967."
Climate clincher
The original dating in 1967 found the fossils to be 130,000 years old.
This was based on the decay rate of radioactive uranium atoms contained in oyster shells found near the skulls - "but that date should always have been taken with a pinch of salt", Professor Brown told BBC News.
"Molluscs are not really very good for that kind of thing."
The new results, though, are regarded as far more robust. They depend on the known decay rate of radioactive atoms of potassium-40 into the gas argon-40 in feldspar mineral crystals.
These crystals were retrieved from chunks of pumice in volcanic ash layers above and below the skulls.
They suggested the specimens must be between 104,000 and 196,000 years old - but with some additional climate evidence on ancient flooding in the region, the team was able to show the Omo finds were actually very close to the 196,000-year mark.
Dr Chris Stringer, from London's Natural History Museum, worked on the skulls more than 20 years ago. He told BBC News: "I was of the opinion that Omo I was a modern human - Omo II seemed much more primitive. So, from my point of view I thought Omo II might be older than Omo I.
"But it seems that they are about the same age and that shows that the populations in Africa at that time were very variable. They show different mixtures of primitive and modern characteristics."
The previous oldest Homo sapiens skulls were uncovered in sediments near a village called Herto in the Afar region in the east of Ethiopia. These were dated to between 154,000 and 160,000 years old.
To be human
Although researchers are pushing at the evolutionary base of our species, they still have much to discover in terms of these early people's behaviour.
Professor Brown explains: "...the cultural aspects of humanity in most cases appear much later in the record - only 50,000 years ago - which would mean 150,000 years of Homo sapiens without cultural stuff, such as evidence of eating fish, of harpoons, anything to do with music (flutes and that sort of thing), needles, even tools.
"This stuff all comes in very late, except for stone knife blades, which appeared between 50,000 and 200,000 years ago, depending on whom you believe."
Professor John Fleagle, of New York state's Stony Brook University, adds: "There is a huge debate in the archaeological literature regarding the first appearance of modern aspects of behaviour such as bone carving for religious reasons, or tools, ornamentation (bead jewellery and such), drawn images, and arrowheads.
"They only appear as a coherent package about 50,000 years ago, and the first modern humans that left Africa between 50,000 and 40,000 years ago seem to have had the full set.
"As modern human anatomy is documented at earlier and earlier sites, it becomes evident that there was a great time gap between the appearance of the modern skeleton and 'modern behaviour'."
The age estimate comes from a re-dating of Ethiopian rock layers close to those that yielded the remarkable fossils.
The skulls, known as Omo I and II, push back the known presence of Homo sapiens in Africa by 40,000 years.
The latest dating work is reported in the science journal Nature.
It puts the specimens close to the time expected for the evolutionary emergence of our species. Genetic studies have indicated Homo sapiens arose in East Africa - possibly Ethiopia or Tanzania - just over 200,000 years ago.
"These are the earliest known examples of our own species and that suggests they lived earlier still," commented Nature senior editor Dr Henry Gee.
"But I am not sure how much further back you could go and still have Homo sapiens - before they graded into some other, earlier species," he told the BBC News website.
Dig return
The skulls were first brought to the attention of the world by the famous fossil hunter Richard Leakey, whose team unearthed the specimens in sediments along the Omo River in southernmost Ethiopia, near the town of Kibish.
They found the skull (minus the face) and partial skeleton (parts of arms, legs, feet and the pelvis) of Omo I, and the top and back of the skull of Omo II.
Now, a three-man Australian-US team - Ian McDougall, Frank Brown and John Fleagle - has re-evaluated the Leakey finds.
The team even returned to the original excavation area, using old scientific reports, photographs and film to identify the precise dig co-ordinates.
"Omo I actually has the better information on it," explained co-author Professor Brown, from the University of Utah's College of Mines and Earth Sciences.
"[The records and maps] are correct and we actually went back and found a few more pieces of the skeleton and some of them glue on to the pieces that were found in 1967."
Climate clincher
The original dating in 1967 found the fossils to be 130,000 years old.
This was based on the decay rate of radioactive uranium atoms contained in oyster shells found near the skulls - "but that date should always have been taken with a pinch of salt", Professor Brown told BBC News.
"Molluscs are not really very good for that kind of thing."
The new results, though, are regarded as far more robust. They depend on the known decay rate of radioactive atoms of potassium-40 into the gas argon-40 in feldspar mineral crystals.
These crystals were retrieved from chunks of pumice in volcanic ash layers above and below the skulls.
They suggested the specimens must be between 104,000 and 196,000 years old - but with some additional climate evidence on ancient flooding in the region, the team was able to show the Omo finds were actually very close to the 196,000-year mark.
Dr Chris Stringer, from London's Natural History Museum, worked on the skulls more than 20 years ago. He told BBC News: "I was of the opinion that Omo I was a modern human - Omo II seemed much more primitive. So, from my point of view I thought Omo II might be older than Omo I.
"But it seems that they are about the same age and that shows that the populations in Africa at that time were very variable. They show different mixtures of primitive and modern characteristics."
The previous oldest Homo sapiens skulls were uncovered in sediments near a village called Herto in the Afar region in the east of Ethiopia. These were dated to between 154,000 and 160,000 years old.
To be human
Although researchers are pushing at the evolutionary base of our species, they still have much to discover in terms of these early people's behaviour.
Professor Brown explains: "...the cultural aspects of humanity in most cases appear much later in the record - only 50,000 years ago - which would mean 150,000 years of Homo sapiens without cultural stuff, such as evidence of eating fish, of harpoons, anything to do with music (flutes and that sort of thing), needles, even tools.
"This stuff all comes in very late, except for stone knife blades, which appeared between 50,000 and 200,000 years ago, depending on whom you believe."
Professor John Fleagle, of New York state's Stony Brook University, adds: "There is a huge debate in the archaeological literature regarding the first appearance of modern aspects of behaviour such as bone carving for religious reasons, or tools, ornamentation (bead jewellery and such), drawn images, and arrowheads.
"They only appear as a coherent package about 50,000 years ago, and the first modern humans that left Africa between 50,000 and 40,000 years ago seem to have had the full set.
"As modern human anatomy is documented at earlier and earlier sites, it becomes evident that there was a great time gap between the appearance of the modern skeleton and 'modern behaviour'."
Astronomers find star-less galaxy
Astronomers say they have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter.
The team, led by Cardiff University, claimed it is the first to be detected.
A dark galaxy is an area in the Universe containing a large amount of mass that rotates like a galaxy, but contains no stars.
It was found 50 million light years away using radio telescopes in Cheshire and Puerto Rico.
The unknown material that is thought to hold these dark galaxies together is known as 'dark matter', but scientists still know very little about what that is.
The five-year research has involved studying the distribution of hydrogen atoms throughout the Universe, estimated by looking at the rotation of galaxies and the speed at which their components moved.
Hydrogen gas releases radiation that can be detected at radio wavelengths.
In the Virgo cluster of galaxies, they found a mass of hydrogen atoms a hundred million times the mass of the Sun.
The mysterious galaxy has been called VIRGOHI21.
Similar objects that have previously been discovered have since turned out to contain stars or be remnants of two galaxies colliding.
However, the scientists from the UK, France, Italy and Australia found no visible trace of any stars, and no galaxies nearby that would suggest a collision.
Dr Robert Minchin, of Cardiff University, said: "From its speed, we realised that VIRGOHI21 was a thousand times more massive than could be accounted for by the observed hydrogen atoms alone.
"If it were an ordinary galaxy, then it should be quite bright and would be visible with a good amateur telescope."
The astronomers say it is hard to study the universe's dark, hidden objects because of the Earth's proximity to the Sun.
They liken it to looking out at the darkest night from a well-lit room - it is easy to make out street lights but not trees, hedges and mountains.
Astronomers say it marks an important breakthrough because, according to cosmological models, dark matter is five times more abundant than the ordinary (baryonic) matter that makes up everything we can see and touch.
Another of the Cardiff team, Dr Jon Davies, added: "The Universe has all sorts of secrets still to reveal to us, but this shows that we are beginning to understand how to look at it in the right way. It's a really exciting discovery."
The team, led by Cardiff University, claimed it is the first to be detected.
A dark galaxy is an area in the Universe containing a large amount of mass that rotates like a galaxy, but contains no stars.
It was found 50 million light years away using radio telescopes in Cheshire and Puerto Rico.
The unknown material that is thought to hold these dark galaxies together is known as 'dark matter', but scientists still know very little about what that is.
The five-year research has involved studying the distribution of hydrogen atoms throughout the Universe, estimated by looking at the rotation of galaxies and the speed at which their components moved.
Hydrogen gas releases radiation that can be detected at radio wavelengths.
In the Virgo cluster of galaxies, they found a mass of hydrogen atoms a hundred million times the mass of the Sun.
The mysterious galaxy has been called VIRGOHI21.
Similar objects that have previously been discovered have since turned out to contain stars or be remnants of two galaxies colliding.
However, the scientists from the UK, France, Italy and Australia found no visible trace of any stars, and no galaxies nearby that would suggest a collision.
Dr Robert Minchin, of Cardiff University, said: "From its speed, we realised that VIRGOHI21 was a thousand times more massive than could be accounted for by the observed hydrogen atoms alone.
"If it were an ordinary galaxy, then it should be quite bright and would be visible with a good amateur telescope."
The astronomers say it is hard to study the universe's dark, hidden objects because of the Earth's proximity to the Sun.
They liken it to looking out at the darkest night from a well-lit room - it is easy to make out street lights but not trees, hedges and mountains.
Astronomers say it marks an important breakthrough because, according to cosmological models, dark matter is five times more abundant than the ordinary (baryonic) matter that makes up everything we can see and touch.
Another of the Cardiff team, Dr Jon Davies, added: "The Universe has all sorts of secrets still to reveal to us, but this shows that we are beginning to understand how to look at it in the right way. It's a really exciting discovery."
Microbes survive deep permafrost / By Becky McCall
Microbes in the Alaskan permafrost have been found living in temperatures as low as minus 40 degrees Celsius.
The discovery raises concerns that the activity of these bacteria, once thought inactive at such extreme temperatures, could be making a considerable contribution to greenhouse gas production.
Scientists found that bacteria taken from the Alaskan tundra soil release gases during energy production whilst apparently in a frozen state.
This runs contrary to textbook biology, which dictates the need for freely available water to allow these single-celled life forms to function.
Dr Nicolai Panikov, from the Stevens Institute of Technology, New Jersey, US, and colleague, Dr Vladimir Romanovsky, from the University of Alaska, tested the mixture of bacteria and registered the production of gases; by-products of metabolism.
"Typically, bacteria in the permafrost are in a dormant state but we have found that they reproduce very slowly and respire producing gases including CO2 and methane when frozen," Dr Panikov said.
Frozen cells
Water is considered essential for life, whether at the single-cell level, such as in bacteria, or in larger animals. It helps the exchange of essential gases between the bacteria and the outside.
So the discovery of bacteria, thought to be frozen solid at such extreme temperatures, raises many interesting questions about the survival mechanisms used in these harsh conditions.
"We have found that it is not pure ice but the mixture of ice and mineral particles that allows for the exchange of gases," Dr Panikov told BBC News website.
"One explanation is that the bacteria oxidise substances in the permafrost to generate heat inside themselves or that these microbes create anti-freeze compounds that keep water liquefied inside their cells."
Permafrost covers about one fifth of the world's land surface and is frozen over most of Alaska, Northern Canada and Siberia, from depths of a few centimetres to 300m (1,000ft). Long considered a major carbon sink, recent evidence suggests that the permafrost is thawing as global temperatures rise.
Even a small increase in temperature will have a significant increase on the rate of metabolic activity in these bacteria affecting the biochemistry of the soil.
If the activity of these bacteria was incorporated into models of climate change prediction, the permafrost may take on the role of a source of greenhouse gases rather than a sink.
"Our results predict the rate of actual degradation- it shows that it's not necessary for the temperature to rise to freezing point for the stimulation of the degradation process," said Dr Panikov.
Knut Stamnes, Professor of atmospheric physics at Stevens, believes that as the permafrost thaws the greatest threat comes from methane.
"Methane is more important than CO2 in producing greenhouse gases because the atmosphere is relatively saturated with CO2 but not with methane yet. This is a new area for exploration." said Professor Stamnes.
Life forms on other planets
In fact, methane gas was recently found by the European Space Agency (Esa) Mars Express mission in the lower atmosphere of the Red Planet and has been associated with ground ice, fuelling speculation about a biological source of the methane.
Professor Dawn Sumner, associate professor of geology at the University of California-Davis, advises the US space agency (Nasa) Mars Exploration and Analysis Group.
She believes that the 2007 Phoenix Lander mission to Mars will have increased access to potentially habitable zones and that if life does exist, it is likely to be found in ice first.
"Panikov's results could extend our concept of possible habitable zones to colder temperatures than previously envisioned," said Professor Sumner.
"If low temperature life does exist on another planet, we are likely to find it in ice first because we have identified many very cold, icy environments, but very few environments with liquid water, especially ones that are accessible to robotic missions."
More details on the bacteria research are due to be published in the Soil Biology & Biochemistry journal.
The discovery raises concerns that the activity of these bacteria, once thought inactive at such extreme temperatures, could be making a considerable contribution to greenhouse gas production.
Scientists found that bacteria taken from the Alaskan tundra soil release gases during energy production whilst apparently in a frozen state.
This runs contrary to textbook biology, which dictates the need for freely available water to allow these single-celled life forms to function.
Dr Nicolai Panikov, from the Stevens Institute of Technology, New Jersey, US, and colleague, Dr Vladimir Romanovsky, from the University of Alaska, tested the mixture of bacteria and registered the production of gases; by-products of metabolism.
"Typically, bacteria in the permafrost are in a dormant state but we have found that they reproduce very slowly and respire producing gases including CO2 and methane when frozen," Dr Panikov said.
Frozen cells
Water is considered essential for life, whether at the single-cell level, such as in bacteria, or in larger animals. It helps the exchange of essential gases between the bacteria and the outside.
So the discovery of bacteria, thought to be frozen solid at such extreme temperatures, raises many interesting questions about the survival mechanisms used in these harsh conditions.
"We have found that it is not pure ice but the mixture of ice and mineral particles that allows for the exchange of gases," Dr Panikov told BBC News website.
"One explanation is that the bacteria oxidise substances in the permafrost to generate heat inside themselves or that these microbes create anti-freeze compounds that keep water liquefied inside their cells."
Permafrost covers about one fifth of the world's land surface and is frozen over most of Alaska, Northern Canada and Siberia, from depths of a few centimetres to 300m (1,000ft). Long considered a major carbon sink, recent evidence suggests that the permafrost is thawing as global temperatures rise.
Even a small increase in temperature will have a significant increase on the rate of metabolic activity in these bacteria affecting the biochemistry of the soil.
If the activity of these bacteria was incorporated into models of climate change prediction, the permafrost may take on the role of a source of greenhouse gases rather than a sink.
"Our results predict the rate of actual degradation- it shows that it's not necessary for the temperature to rise to freezing point for the stimulation of the degradation process," said Dr Panikov.
Knut Stamnes, Professor of atmospheric physics at Stevens, believes that as the permafrost thaws the greatest threat comes from methane.
"Methane is more important than CO2 in producing greenhouse gases because the atmosphere is relatively saturated with CO2 but not with methane yet. This is a new area for exploration." said Professor Stamnes.
Life forms on other planets
In fact, methane gas was recently found by the European Space Agency (Esa) Mars Express mission in the lower atmosphere of the Red Planet and has been associated with ground ice, fuelling speculation about a biological source of the methane.
Professor Dawn Sumner, associate professor of geology at the University of California-Davis, advises the US space agency (Nasa) Mars Exploration and Analysis Group.
She believes that the 2007 Phoenix Lander mission to Mars will have increased access to potentially habitable zones and that if life does exist, it is likely to be found in ice first.
"Panikov's results could extend our concept of possible habitable zones to colder temperatures than previously envisioned," said Professor Sumner.
"If low temperature life does exist on another planet, we are likely to find it in ice first because we have identified many very cold, icy environments, but very few environments with liquid water, especially ones that are accessible to robotic missions."
More details on the bacteria research are due to be published in the Soil Biology & Biochemistry journal.
