NEWS: Purdue Researchers Determine Age Of Fossilized Human Ancestor
Peggy
This is pretty cool! Peggy
http://www.sciencedaily.com/releases/2003/04/030425071144.htm
Purdue Researchers Determine Age Of Fossilized Human Ancestor
WEST LAFAYETTE, Ind. - In a finding that could shed light on the
earliest origins of mankind, fossil remains found in South Africa of an
ancestral human species have proven far older than expected when
evaluated by a Purdue University research team.
Purdue's Darryl Granger and Marc Caffee have determined the age of a
fossilized skeleton thought to be an Australopithecus - a genus of
African hominids from which humanity is thought to have developed - by
measuring the radioactivity of the cave sediments in which the skeleton
was buried millions of years ago. Their measurement technique, generally
used to estimate the age of geological formations such as glaciated
valleys and river terraces, has never before been used to date
biological fossils.
"By dating the sediments surrounding the fossil skeleton, we have
determined that this species reached southern Africa approximately 4
million years ago," said Granger, associate professor of earth and
atmospheric sciences in Purdue's School of Science. "If the skeleton is
indeed an Australopithecus, as we believe, the findings could mean that
these hominids were present in the area far earlier than is generally
accepted."
The research appears in Friday's (4/25) issue of Science.
Tracing the development and spread of the hominid species that may have
been mankind's ancestor is an arduous process, and it is difficult to
determine what happened because precisely dated fossil records are hard
to come by. Many such fossils have been found in eastern Africa's Rift
Valley, a region that was geologically active when Australopithecus
walked the Earth. The abundance of lake sediments and volcanic ash that
often surrounds Rift Valley hominid fossils provide good clues as to
their age. But there is no such luck with similar fossils from South
Africa, a region that also is rich in hominid remains but lacks the
definitive geological clues that are present in the Rift Valley.
T.C. Partridge and R.J. Clarke, researchers from the University of the
Witwatersrand in South Africa, were thus confronted with a mixed
blessing when, in 1997, they discovered a nearly complete skeleton of
what appeared to be an Australopithecus buried in the sediments on the
floor of the Sterkfontein cave in central South Africa. The fossil was
well preserved, but its age was uncertain. It was more than 2 million
years old, but how much more? The answer to that question would affect
theories of how and when Australopithecus spread through Africa.
"Their initial estimate of 3.3 million years provoked a lot of
controversy," Granger said. "Few thought that Australopithecus had
traveled so far so long ago, and scientists wanted more proof. If the
estimate was accurate, it might require a rethinking of human prehistory."
A firmer answer would require the innovative use of a particle
accelerator half a world away at Purdue in Indiana, where Granger was
using radioactive isotopes in sediment to determine the age of rivers
and caves.
Dating fossils by examining the minute quantities of radioactive
elements they contain is not a new technique in archaeology. Carbon-14,
a radioactive isotope that slowly decays as centuries pass, has been a
common benchmark for dating many human fossils; the more carbon-14 has
decayed in a sample, the older it must be. The speed at which carbon-14
decays, called its half-life, is only 5,730 years. This means that after
a few millennia, the isotope is no longer useful to mark a fossil's age.
"Once your fossil is older than 50,000 years, its carbon-14 is nearly
gone," Granger said. "We knew the South African fossils were at least 2
million years old, so it was clear we needed another way to establish
their age."
Granger, a physics major as an undergraduate, eventually became an earth
scientist when he developed an interest in studying the age and changes
in mountains and river beds, geological formations that are often many
millions of years old. Rather than use carbon-14 to date his landscapes,
he looked for isotopes with far longer half-lives - and found them in
aluminum-26 and beryllium-10. These elements often form in common quartz
when it is on the Earth's surface and exposed to cosmic rays.
"When radiation from outer space strikes silicon and oxygen atoms in a
quartz crystal, they split into aluminum-26 and beryllium-10, both of
which have half-lives of around a million years," Granger said. "Because
they decay so slowly, they allow you to reach back much further in
history than you can using carbon-14."
The use of aluminum and beryllium for radiometric dating had only been
around for a few years when Granger began to use it on cave sediments.
The technique was not widely known outside geological circles, so when
he heard about the Australopithecus discovery, he contacted the South
African scientists who found the skeleton and asked if he could be of
assistance.
"It was the first time this method had been used to determine the age of
something that had been alive," Granger said. "But based on the
evidence, we found that the fossil was even older than the initial
estimate."
Granger and Caffee, of Purdue's physics department, analyzed samples of
the skeleton in Purdue's accelerator mass spectrometer, a device capable
of detecting the infinitesimal quantities of radioactive aluminum and
beryllium in the samples.
"We found that the skeleton was between 3.5 and 4.5 million years old,"
Granger said. "That's admittedly quite a large window of possibility,
but even if it's on the young side, it still puts Australopithecus in
southern Africa far earlier than expected."
The significance for anthropologists would be the possibility that
mankind's earliest ancestors were a different species than scientists
generally believe.
"Early hominid finds in eastern Africa have traditionally been regarded
as the base populations from which all later hominids sprung," said
Melissa Remis, associate professor of anthropology in Purdue's School of
Liberal Arts. "An earlier hominid find in southern Africa, whatever the
species might be, could force a rethinking of what that base population
might have been."
Granger said he hesitated to speculate on the broader significance of
the findings, but he hopes the technique will prove useful in other
investigations into prehuman history.
This research was funded in part by the National Science Foundation.
http://www.sciencedaily.com/releases/2003/04/030425071144.htm
Purdue Researchers Determine Age Of Fossilized Human Ancestor
WEST LAFAYETTE, Ind. - In a finding that could shed light on the
earliest origins of mankind, fossil remains found in South Africa of an
ancestral human species have proven far older than expected when
evaluated by a Purdue University research team.
Purdue's Darryl Granger and Marc Caffee have determined the age of a
fossilized skeleton thought to be an Australopithecus - a genus of
African hominids from which humanity is thought to have developed - by
measuring the radioactivity of the cave sediments in which the skeleton
was buried millions of years ago. Their measurement technique, generally
used to estimate the age of geological formations such as glaciated
valleys and river terraces, has never before been used to date
biological fossils.
"By dating the sediments surrounding the fossil skeleton, we have
determined that this species reached southern Africa approximately 4
million years ago," said Granger, associate professor of earth and
atmospheric sciences in Purdue's School of Science. "If the skeleton is
indeed an Australopithecus, as we believe, the findings could mean that
these hominids were present in the area far earlier than is generally
accepted."
The research appears in Friday's (4/25) issue of Science.
Tracing the development and spread of the hominid species that may have
been mankind's ancestor is an arduous process, and it is difficult to
determine what happened because precisely dated fossil records are hard
to come by. Many such fossils have been found in eastern Africa's Rift
Valley, a region that was geologically active when Australopithecus
walked the Earth. The abundance of lake sediments and volcanic ash that
often surrounds Rift Valley hominid fossils provide good clues as to
their age. But there is no such luck with similar fossils from South
Africa, a region that also is rich in hominid remains but lacks the
definitive geological clues that are present in the Rift Valley.
T.C. Partridge and R.J. Clarke, researchers from the University of the
Witwatersrand in South Africa, were thus confronted with a mixed
blessing when, in 1997, they discovered a nearly complete skeleton of
what appeared to be an Australopithecus buried in the sediments on the
floor of the Sterkfontein cave in central South Africa. The fossil was
well preserved, but its age was uncertain. It was more than 2 million
years old, but how much more? The answer to that question would affect
theories of how and when Australopithecus spread through Africa.
"Their initial estimate of 3.3 million years provoked a lot of
controversy," Granger said. "Few thought that Australopithecus had
traveled so far so long ago, and scientists wanted more proof. If the
estimate was accurate, it might require a rethinking of human prehistory."
A firmer answer would require the innovative use of a particle
accelerator half a world away at Purdue in Indiana, where Granger was
using radioactive isotopes in sediment to determine the age of rivers
and caves.
Dating fossils by examining the minute quantities of radioactive
elements they contain is not a new technique in archaeology. Carbon-14,
a radioactive isotope that slowly decays as centuries pass, has been a
common benchmark for dating many human fossils; the more carbon-14 has
decayed in a sample, the older it must be. The speed at which carbon-14
decays, called its half-life, is only 5,730 years. This means that after
a few millennia, the isotope is no longer useful to mark a fossil's age.
"Once your fossil is older than 50,000 years, its carbon-14 is nearly
gone," Granger said. "We knew the South African fossils were at least 2
million years old, so it was clear we needed another way to establish
their age."
Granger, a physics major as an undergraduate, eventually became an earth
scientist when he developed an interest in studying the age and changes
in mountains and river beds, geological formations that are often many
millions of years old. Rather than use carbon-14 to date his landscapes,
he looked for isotopes with far longer half-lives - and found them in
aluminum-26 and beryllium-10. These elements often form in common quartz
when it is on the Earth's surface and exposed to cosmic rays.
"When radiation from outer space strikes silicon and oxygen atoms in a
quartz crystal, they split into aluminum-26 and beryllium-10, both of
which have half-lives of around a million years," Granger said. "Because
they decay so slowly, they allow you to reach back much further in
history than you can using carbon-14."
The use of aluminum and beryllium for radiometric dating had only been
around for a few years when Granger began to use it on cave sediments.
The technique was not widely known outside geological circles, so when
he heard about the Australopithecus discovery, he contacted the South
African scientists who found the skeleton and asked if he could be of
assistance.
"It was the first time this method had been used to determine the age of
something that had been alive," Granger said. "But based on the
evidence, we found that the fossil was even older than the initial
estimate."
Granger and Caffee, of Purdue's physics department, analyzed samples of
the skeleton in Purdue's accelerator mass spectrometer, a device capable
of detecting the infinitesimal quantities of radioactive aluminum and
beryllium in the samples.
"We found that the skeleton was between 3.5 and 4.5 million years old,"
Granger said. "That's admittedly quite a large window of possibility,
but even if it's on the young side, it still puts Australopithecus in
southern Africa far earlier than expected."
The significance for anthropologists would be the possibility that
mankind's earliest ancestors were a different species than scientists
generally believe.
"Early hominid finds in eastern Africa have traditionally been regarded
as the base populations from which all later hominids sprung," said
Melissa Remis, associate professor of anthropology in Purdue's School of
Liberal Arts. "An earlier hominid find in southern Africa, whatever the
species might be, could force a rethinking of what that base population
might have been."
Granger said he hesitated to speculate on the broader significance of
the findings, but he hopes the technique will prove useful in other
investigations into prehuman history.
This research was funded in part by the National Science Foundation.