Astronomy

A 2.2-billion-year-old crater is Earth’s oldest recorded meteorite impact

A 70-kilometer-wide crater in Western Australia has officially earned the title of Earth’s oldest known recorded impact. Yarrabubba crater is a spry 2.2 billion years old, plus or minus 5 million years, researchers report January 21 in Nature Communications.   

Moving tectonic plates along with erosion have wiped away much of
the evidence
for many craters older than 2 billion years, leaving a gap in our understanding
of how long-ago meteorite impacts may have affected the planet’s life and
atmosphere (SN: 12/18/18). Scientists
have uncovered ancient impact material older than 2.4 billion years from sites elsewhere
in Western Australia and South Africa, but no corresponding craters.

Yarrabubba, located on one of Earth’s oldest patches of crust called
Yilgarn craton, adds more than 200 million years to the impact record. The
previous record-holder was Vredefort crater in South Africa.

Scientists had estimated Yarrabubba to be between 2.6 billion and
1.2 billion years old, based on previous research dating rocks around the
impact site. In the new study, researchers pinpointed the crater’s age by dating
microstructures in crystallized rock that formed when the impact occurred.

Dating Earth’s oldest crater was not the only exciting finding, says
study coauthor Timmons Erickson, a geologist at NASA’s Astromaterials Research &
Exploration Science Division in Houston. The crater’s age puts the impact at
the end of an ancient glacial period. A computer simulation suggests that a Yarrabubba-sized
impact would have released up to 200 trillion kilograms of water vapor into the
atmosphere, which the researchers say could have warmed the planet and melted ice
sheets.

The first U.S. case of a new coronavirus has been confirmed

A man in Seattle has been
confirmed as the first U.S. case of a novel coronavirus that emerged in central China, where it has killed
six people and sickened hundreds more in recent weeks, according to the U.S.
Centers for Disease Control and Prevention.

Officials are also ramping
up health screenings at U.S. airports, after Chinese public health officials said January 20
that the virus can spread from person to person — a factor that raises concerns
of an international epidemic emerging.

It’s still unclear how easily the
virus spreads between humans. The World Health Organization said it would
convene an emergency committee on January 22 in Geneva to decide whether to
declare a global health emergency. 

“The confirmation that
human-to-human spread with this virus is occurring in Asia certainly raises our
level of concern,” said Nancy Messonnier,
director of the CDC’s National Center for Immunization and Respiratory
Diseases, during a telephone news conference on January 21. However, the agency
believes the risk “to the American public at large remains low at this time.”

The Seattle patient in his 30s was
diagnosed after seeing a doctor for respiratory symptoms, Messonnier said. The man had returned last week
from Wuhan, and is no longer “clinically ill,” she said.

The first people reported to have
the pneumonia-like illness became sick in December, after visiting a wild
animal market in the central Chinese city of Wuhan. Officials soon confirmed
that the outbreak was caused by a novel
coronavirus
(SN: 1/10/20) — the same family of viruses that causes
severe acute respiratory syndrome, or SARS. 

On January 20, China’s lead
scientist monitoring the outbreak, Dr. Zhong Nanshan, gave a statement on Chinese
state television confirming that at least two patients who had never been to
Wuhan had been infected by family members who recently had traveled to the
city. At least 15 health care workers are also among at least 278 cases
reported by China.

Scientists are still trying to understand how dangerous the virus is. Most of the six people who died had been suffering with a preexisting health condition, says Jennifer Nuzzo, an epidemiologist at the Johns Hopkins Center for Health Security in Baltimore. And it’s unclear if the recent jump in cases is due to the virus spreading further, or simply heightened surveillance, she says.

Also unclear, she says, is how
exactly the virus spreads. “Can a sick person easily transmit the disease when
they’re out in the community? Or can it only be transmitted in risky situations,
for example, when a health care worker is caring for a patient and their
personal protective equipment fails?”

Experts also need more information about
newer cases not directly tied to the Wuhan animal market, she says. Detailed
patient histories can help in tracing sources of infection, but that
information has yet to reach the international public health community, she
says.

The severity of illness caused by the
virus also is unclear, with details about the condition of patients in China
yet to be shared widely, says infectious disease
physician Amesh Adalja, also at Johns Hopkins Center for Health Security. “Are
they requiring oxygen therapy? Intravenous fluids? Those types of questions are
really important in helping us know where to place this outbreak in terms of
risk,” Adalja says.

The CDC said
passengers arriving on direct or connecting flights from Wuhan would be
funneled through five international airports conducting health
screenings
— in New York City, Atlanta, Chicago, Los
Angeles and San Francisco. Cases have also been reported in people who had
traveled from China to Thailand, Japan and South Korea. Russian and Canadian
airports are also screening some arriving passengers.

“We’re taking a
proactive approach,” the CDC’s Messonnier said. “So far CDC staff have screened
over 1,200 individuals” at airports, though none have tested positive for the
virus.

If the WHO decides
to declare the coronavirus a public health emergency, the global
health watchdog may suggest travel restrictions or other recommendations. Amid the 2014 outbreak of another coronavirus called Middle East
respiratory syndrome, or MERS, the WHO “declined to declare MERS an
international emergency,” Nuzzo says. But that was “largely because there
wasn’t evidence of sustained human transmission.”

For the first time, an asteroid has been found nearer to the sun than Venus

For the first time, an asteroid has been found orbiting closer to the sun than Venus — a neighborhood where asteroids are thought to be rare and tricky to find. 

The space rock, designated 2020 AV2, orbits the sun once every 151 days along an elongated trajectory that keeps it between the orbits of Mercury and Venus. Such asteroids — known as Vatiras — were first predicted in 2012, but until now, no one had ever found one.

Asteroid 2020 AV2 was found January 4 by researchers at the Palomar Observatory in southern California. Following an alert by the International Astronomical Union’s Minor Planet Center, observers around the world confirmed and refined the asteroid’s orbit.

Asteroids that live inside Earth’s orbit are notoriously difficult to find because they spend most of their time close to the sun (SN: 4/3/15). Astronomers can therefore look for such objects only during brief periods of twilight. 

According to computer simulations, Vatiras are rare, making up only 0.22 percent of so-called near-Earth objects. Vatiras probably start their lives in the main asteroid belt between Mars and Jupiter and end up between Mercury and Venus after a series of close encounters with rocky planets. Simulations suggest that Vatiras typically don’t remain in orbit around the sun for long — continued gravitational tugs from nearby worlds and uneven solar heating eventually send most crashing into a planet or grazing the sun.

How bacteria create flower art

When sticky bacteria meet roaming
bacteria in a petri dish, friction between the two can cause flower patterns to
blossom.

Escherichia
coli
bacteria growing on a Jello-like substance called agar tend to stick
to the surface, and colonies of the microbes don’t spread very far. But colonies
of Acinetobacter baylyi expand in
rapidly growing circles as the bacteria crawl on hairlike pili over the agar’s surface.
Neither type of microbe is very exciting to look at on its own, says Lev
Tsimring, a theoretical physicist at the University of California, San Diego.
But “when we mixed them together, we saw these absolutely mind-blowing
structures growing.”

Physical interactions between the two
types of bacteria create floral patterns, he and colleagues found. Mobile A. baylyi “pushes E. coli in front it, sort of like a snowplow,” Tsimring says. But
sticky E. coli dig in their heels,
holding back a wave of A. baylyi like
an elastic band wrapped around a balloon, he says. In some places where there
are fewer E. coli forming a barrier, the
more agile bacteria break through, painting petals as they shove their reluctant
neighbors forward. Those breakthroughs tend to happen at fairly regular
intervals, creating relatively symmetrical blossoms.

The petal shape that forms depends on
how fast A. baylyi bacteria move, how
well E. coli is stuck to the surface
and the proportions of each type of bacteria at the colony edges. (E. coli must outnumber A. baylyi or the speedy bacteria will
blow right past their more sedentary partners.) Tsimring’s team described the math behind the
blooms
January 14 in eLife.

When E. coli bacteria grow together with a few Acinetobacter baylyi, the microbes can form floral patterns in lab dishes. Here is how one bacterial “flower” grew.

Such equations have been used to explain
how reactions between chemicals might produce Turing
patterns
— regular, repeating patterns found in nature, such as spots or
stripes on animals’ coats (SN: 12/21/15).
The new research shows that, in addition to chemicals, scientists should
consider how mechanical forces help shape patterns too, Tsimring says.

Understanding how bacteria grow in mixed
company may shed light on how biofilms form, enabling researchers to devise
better ways to disrupt these communities composed of different types of
microbes. Some biofilms have been linked to stubborn
infections
(SN: 5/20/16).

A naturalist writes an homage to bird migration

A Season on the Wind
Kenn Kaufman
Houghton Mifflin Harcourt, $26

A tiny blackpoll warbler, a bird no
heavier than a ballpoint pen, makes an epic journey each year. In fall, the
bird flies some 10,000 kilometers from its breeding grounds in Alaska or Canada
to its winter retreat in South America. In the spring, the bird undertakes the
return trip. In his memoir A Season on
the Wind,
naturalist Kenn Kaufman shares his awe for the miraculous
round-trip flight this warbler makes every year.

A backdrop to the book is
northwestern Ohio’s “Biggest Week in American Birding,” headquartered at Magee
Marsh in Oak Harbor. As northbound birds like the blackpoll drop into the
marshes that line Lake Erie’s southern shore in early May, so do the birders —
who come to see the hundreds of migratory bird species that stop here to rest and
feed every spring.

Kaufman intertwines his personal
reminiscences with stories of individual bird species and migration science.
His observations are intensely personal, yet also offer insight into the shared
experience of a global community of birders. 
Of the birders who flock from all over the world to Magee Marsh in
spring, he writes, “I see people arriving here with mild curiosity and leaving
with the spark of an intense, passionate interest.” His memoir reads as a love
letter to bird migration, his adopted home of northwestern Ohio and his wife,
Kimberly.

Kaufman has authored a dozen
popular guidebooks to the birds, insects and mammals of North America. In A Season on the Wind, he returns to the
storytelling that won over readers of his classic 1997 memoir Kingbird Highway. That award-winning
book told of his exploits hitchhiking around North America as a teenager in the
1970s in pursuit of a birding “big year”
competing with others to see the greatest number of species in a single
calendar year.

Kaufman’s rich and poetic writing
transforms a little brown winter wren into a polychrome.  He writes, “There are a hundred shades of
brown, from soft and subtle to deep and rich, the browns of hot chocolate, warm
earth, tawny terra-cotta altars in ancient temples, chestnut stallions running
through red-rock canyons — a wilderness of browns.”

Such writing will draw in even those readers with little knowledge of birds and may inspire novices to give bird-watching a try. And for the avid birder, Kaufman offers a soaring flight through a favorite subject.


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