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1 There's a dimmer switch inside the sun that causes its brightness to rise
and fall on timescales of around 100,000 years - exactly the same period as
between ice ages on Earth. So says a physicist who has created a computer model
of our star's core.
2 Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled
the effect of temperature fluctuations in the sun's interior. According to the
standard view, the temperature of the sun's core is held constant by the
opposing pressures of gravity and nuclear fusion. However, Ehrlich believed that
slight variations should be possible.
3 He took as his starting point the work of Attila Grandpierre of the Konkoly
Observatory of the Hungarian Academy of Sciences. In 2005, Grandpierre and a
collaborator, Gábor ágoston, calculated that magnetic fields in the sun's core
could produce small instabilities in the solar plasma. These instabilities would
induce localised oscillations in temperature.
4 Ehrlich's model shows that whilst most of these oscillations cancel each
other out, some reinforce one another and become long-lived temperature
variations. The favoured frequencies allow the sun's core temperature to
oscillate around its average temperature of 13.6 million kelvin in cycles
lasting either 100,000 or 41,000 years. Ehrlich says that random interactions
within the sun's magnetic field could flip the fluctuations from one cycle
length to the other.
5 These two timescales are instantly recognisable to anyone familiar with
Earth's ice ages: for the past million years, ice ages have occurred roughly
every 100,000 years. Before that, they occurred roughly every 41,000 years.
6 Most scientists believe that the ice ages are the result of subtle changes
in Earth's orbit, known as the Milankovitch cycles. One such cycle describes the
way Earth's orbit gradually changes shape from a circle to a slight ellipse and
back again roughly every 100,000 years. The theory says this alters the amount
of solar radiation that Earth receives, triggering the ice ages. However, a
persistent problem with this theory has been its inability to explain why the
ice ages changed frequency a million years ago.
7 "In Milankovitch, there is certainly no good idea why the frequency should
change from one to another," says Neil Edwards, a climatologist at the Open
University in Milton Keynes, UK. Nor is the transition problem the only one the
Milankovitch theory faces. Ehrlich and other critics claim that the temperature
variations caused by Milankovitch cycles are simply not big enough to drive ice
ages.
8 However, Edwards believes the small changes in solar heating produced by
Milankovitch cycles are then amplified by feedback mechanisms on Earth. For
example, if sea ice begins to form because of a slight cooling, carbon dioxide
that would otherwise have found its way into the atmosphere as part of the
carbon cycle is locked into the ice. That weakens the greenhouse effect and
Earth grows even colder.
9 According to Edwards, there is no lack of such mechanisms. "If you add
their effects together, there is more than enough feedback to make Milankovitch
work," he says. "The problem now is identifying which mechanisms are at work."
This is why scientists like Edwards are not yet ready to give up on the current
theory. "Milankovitch cycles give us ice ages roughly when we observe them to
happen. We can calculate where we are in the cycle and compare it with
observation," he says. "I can't see any way of testing [Ehrlich's] idea to see
where we are in the temperature oscillation."
10 Ehrlich concedes this. "If there is a way to test this theory on the sun,
I can't think of one that is practical," he says. That's because variation over
41,000 to 100,000 years is too gradual to be observed. However, there may be a
way to test it in other stars: red dwarfs. Their cores are much smaller than
that of the sun, and so Ehrlich believes that the oscillation periods could be
short enough to be observed. He has yet to calculate the precise period or the
extent of variation in brightness to be expected.
11 Nigel Weiss, a solar physicist at the University of Cambridge, is far from
convinced. He describes Ehrlich's claims as "utterly implausible". Ehrlich
counters that Weiss's opinion is based on the standard solar model, which fails
to take into account the magnetic instabilities that cause the temperature
fluctuations.
Questions 1-4
Complete each of the following statements with One or Two names of the
scientists from the box below.
Write the appropriate letters A-E in boxes 1-4 on your answer sheet.
A. Attila Grandpierre
B. Gábor ágoston
C. Neil Edwards
D. Nigel Weiss
E. Robert Ehrlich
1. ...claims there a dimmer switch inside the sun that causes its brightness
to rise and fall in periods as long as those between ice ages on Earth.
2. ...calculated that the internal solar magnetic fields could produce
instabilities in the solar plasma.
3. ...holds that Milankovitch cycles can induce changes in solar heating on
Earth and the changes are amplified on Earth.
4. ...doesn't believe in Ehrlich's viewpoints at all.
Questions 5-9
Do the following statements agree with the information given in the reading
passage?
In boxes 5-9 on your answer sheet write
TRUE if the statement is true according to the passage
FALSE if the statement is false according to the passage
NOT GIVEN if the information is not given in the passage
5. The ice ages changed frequency from 100,000 to 41,000 years a million
years ago.
6. The sole problem that the Milankovitch theory can not solve is to explain
why the ice age frequency should shift from one to another.
7. Carbon dioxide can be locked artificially into sea ice to eliminate the
greenhouse effect.
8. Some scientists are not ready to give up the Milankovitch theory though
they haven't figured out which mechanisms amplify the changes in solar
heating.
9. Both Edwards and Ehrlich believe that there is no practical way to test
when the solar temperature oscillation begins and when ends.
Questions 10-14
Complete the notes below.
Choose one suitable word from the Reading Passage above for each answer.
Write your answers in boxes 10-14 on your answer sheet.
The standard view assumes that the opposing pressures of gravity and nuclear
fusions hold the temperature ...10...in the sun's interior, but the slight
changes in the earth's ...11... alter the temperature on the earth and cause ice
ages every 100,000 years. A British scientist, however, challenges this view by
claiming that the internal solar magnetic ...12... can induce the temperature
oscillations in the sun's interior. The sun's core temperature oscillates around
its average temperature in ...13... lasting either 100,000 or 41,000 years. And
the ...14... interactions within the sun's magnetic field could flip the
fluctuations from one cycle length to the other, which explains why the ice ages
changed frequency a million years ago.
Don't wash those fossils!
Standard museum practice can wash away DNA.
1.Washing, brushing and varnishing fossils — all standard conservation
treatments used by many fossil hunters and museum curators alike — vastly
reduces the chances of recovering ancient DNA.
2.Instead, excavators should be handling at least some of their bounty with
gloves, and freezing samples as they are found, dirt and all, concludes a paper
in the Proceedings of the National Academy of Sciences today.
3.Although many palaeontologists know anecdotally that this is the best way
to up the odds of extracting good DNA, Eva-Maria Geigl of the Jacques Monod
Institute in Paris, France, and her colleagues have now shown just how important
conservation practices can be.This information, they say, needs to be hammered
home among the people who are actually out in the field digging up bones.
4.Geigl and her colleagues looked at 3,200-year-old fossil bones belonging to
a single individual of an extinct cattle species, called an aurochs.The fossils
were dug up at a site in France at two different times — either in 1947, and
stored in a museum collection, or in 2004, and conserved in sterile conditions
at -20 oC.
5.The team's attempts to extract DNA from the 1947 bones all failed.The newly
excavated fossils, however, all yielded DNA.
6.Because the bones had been buried for the same amount of time, and in the
same conditions, the conservation method had to be to blame says Geigl."As much
DNA was degraded in these 57 years as in the 3,200 years before," she says.
Wash in, wash out
7.Because many palaeontologists base their work on the shape of fossils
alone, their methods of conservation are not designed to preserve DNA, Geigl
explains.
8.The biggest problem is how they are cleaned.Fossils are often washed
together on-site in a large bath, which can allow water — and contaminants in
the form of contemporary DNA — to permeate into the porous bones."Not only is
the authentic DNA getting washed out, but contamination is getting washed in,"
says Geigl.
9.Most ancient DNA specialists know this already, says Hendrik Poinar, an
evolutionary geneticist at McMaster University in Ontario, Canada.But that
doesn't mean that best practice has become widespread among those who actually
find the fossils.
10.Getting hold of fossils that have been preserved with their DNA in mind
relies on close relationships between lab-based geneticists and the excavators,
says palaeogeneticist Svante P bo of the Max Planck Institute for Evolutionary
Anthropology in Leipzig, Germany.And that only occurs in exceptional cases, he
says.
11.P bo's team, which has been sequencing Neanderthal DNA, continually faces
these problems."When you want to study ancient human and Neanderthal remains,
there's a big issue of contamination with contemporary human DNA," he says.
12.This doesn't mean that all museum specimens are fatally flawed, notes P
bo.The Neanderthal fossils that were recently sequenced in his own lab, for
example, had been part of a museum collection treated in the traditional way.But
P bo is keen to see samples of fossils from every major find preserved in line
with Geigl's recommendations — just in case.
Warm and wet
13.Geigl herself believes that, with cooperation between bench and field
researchers, preserving fossils properly could open up avenues of discovery that
have long been assumed closed.
14.Much human cultural development took place in temperate regions.DNA does
not survive well in warm environments in the first place, and can vanish when
fossils are washed and treated.For this reason, Geigl says, most ancient DNA
studies have been done on permafrost samples, such as the woolly mammoth, or on
remains sheltered from the elements in cold caves — including cave bear and
Neanderthal fossils.
15.Better conservation methods, and a focus on fresh fossils, could boost DNA
extraction from more delicate specimens, says Geigl.And that could shed more
light on the story of human evolution.
(640 words nature )
Glossary
Palaeontologists 古生物学家
Aurochs 欧洲野牛
Neanderthal (人类学)尼安德特人，旧石器时代的古人类。
Permafrost (地理)永冻层
Questions 1-6
Answer the following questions by using NO MORE THAN THREE WORDS for each
answer.
1.How did people traditionally treat fossils?
2.What suggestions do Geigl and her colleagues give on what should be done
when fossils are found?
3.What problems may be posed if fossil bones are washed on-site? Name
ONE.
4.What characteristic do fossil bones have to make them susceptible to be
contaminated with contemporary DNA when they are washed?
5.What could be better understood when conservation treatments are
improved?
6.The passage mentioned several animal species studied by researchers.How
many of them are mentioned?
Questions 7-11
Do the following statements agree with the information given in the passage?
Please write TRUE if the statement agrees with the writer FALSE if the statement
does not agree with the writer NOT GIVEN if there is no information about this
in the passage.
7.In their paper published in the Proceedings of the National Academy of
Sciences，Geigl and her colleagues have shown what conservation practices should
be followed to preserve ancient DNA.
8.The fossil bones that Geigl and her colleagues studied are all from the
same aurochs.
9.Geneticists don't have to work on site.
10.Only newly excavated fossil bones using new conservation methods suggested
by Geigl and her colleagues contain ancient DNA.
11.Paabo is still worried about the potential problems caused by treatments
of fossils in traditional way.
Questions 12-13
Complete the following the statements by choosing letter A-D for each
answer.
12.“This information” in paragraph 3 indicates:
[A] It is critical to follow proper practices in preserving ancient DNA.
[B] The best way of getting good DNA is to handle fossils with gloves.
[C] Fossil hunters should wear home-made hammers while digging up bones.
[D] Many palaeontologists know how one should do in treating fossils.
13.The study conducted by Geigl and her colleagues suggests:
[A] the fact that ancient DNA can not be recovered from fossil bones
excavated in the past.
[B] the correlation between the amount of burying time and that of the
recovered DNA.
[C] the pace at which DNA degrades.
[D] the correlation between conservation practices and degradation of
DNA.
