Memento Mori

2012 DA14 will pass close to Earth around midday today (Seattle local time), right as I’ll sit down to lunch.  The 190,000-ton asteroid, identified only last year, will wander within 17,000 miles of us, closer than some of our satellites.  It will not enter the atmosphere and it will not impact our planet.

Not the sun.  The view hours ago near Chelyabinsk.

Not the sun.
The view hours ago near Chelyabinsk.

At 9:15AM local time today, a meteorite entered the atmosphere, burned, partially disintegrated, and exploded over Russia’s Ural Mountains, approximately 125 miles south of the city of Yekaterinburg.  Fragments of the meteorite may have impacted Chebarkul Lake and rural areas across the border in Kazakhstan.  But most of the damage and injuries (up to 1,000 so far) are from the immense shock wave of the atmospheric explosion, which blew out windows and doors in and around the city of Chelyabinsk.  The roof and one wall of a zinc factory collapsed, and the Russian government is using military aircraft to survey additional damage.  Over 20,000 troops have been dispatched to the area to assist in recovery efforts.

The Russian Academy of Sciences believes this meteorite weighed approximately 10 tons, a mere dwarf compared to 2012 DA14.  However, today’s impact in the Ural Mountains is completely unrelated to 2012 DA14‘s flyby.  It’s arrival was complete happenstance; the two objects arrived at Earth from opposite trajectories.  But, this celestial coincidence serves as a sobering reminder of our blue marble’s sometimes perilous position in the cosmos.  As American taxpayers and voters have continuously eroded NASA’s budget, the space agency has struggled to launch missions to survey the heavens for near-Earth asteroids and craft strategies to deflect or destroy potentially dangerous impactors.  Private groups, such as the B612 Foundation, are attempting to fill in the gaps.  But, as today’s celestial duet shows, our current gaze is far too narrow for such a big sky.

Thou art mortal.

Thou art mortal.

In another coincidence, just two days ago Western rite Christians participated in Ash Wednesday, a somber celebration of human mortality inaugurating the 40-day season of Lent.  With today’s worrisome coupling of 2012 DA14‘s passover and the Chelyabinsk bolide impact, it is worth contemplating our mortality in this carefully-balanced biosphere against the backdrop of our occasionally hostile celestial neighborhood.  The skies have warned us before, most notably in an event that occurred just over a century ago a mere 1,100 miles northeast of Chelyabinsk.  In 1908, a meteorite disintegrated in the skies above the remote Siberian wilderness of Tunguska.  The subsequent explosion and shock wave was 1,000 times more powerful than the atomic bombs detonated over Hiroshima and Nagasaki 37 years later, and instantly obliterated over 770 square miles of Siberian forest.  Had Tunguska been a city of millions, the devastation would have been beyond measure.

The meteorite responsible for the Tunguska event is thought to have been approximately the same size as 2012 DA14.

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Parting is Such Sweet Sorrow

Centuries ago, Spanish explorers expected the mythical land of “California” to be a wild and exotic island.  Perhaps they should be applauded for their prescience, for new research published in Nature Communications confirms that California is slowly separating from the rest of North America.  This wrenching process began 7 million years ago and shows no signs of letting up.

Historically, “California” included a large swath of the western United States and Mexico, but today the term refers only to the American state of California (“Upper California” here) and the Mexican states of Baja (“Lower”) California and Baja California Sur (hereafter combined as “Baja California”).  Most of Baja California is a peninsula, separated from the rest of Mexico by the Gulf of California, an inlet of the Pacific Ocean.  To the north, upper California appears firmly attached to the rest of North America.  Baja California was not always such a nonconformist.  Once upon a time, it was firmly attached to the rest of North America.  But slowly and methodically, forces deep within the Earth began to tear Baja California away from the rest of Mexico, opening the Gulf of California.

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The Burst

The years 774 and 775 were eventful times in human history.  Charlemagne conquered the Lombards and began his campaigns into Westphalia.  Heizei, a future emperor of Japan, was born, while Byzantine Emperor Constantine V died and was succeeded by his son Leo IV.

It also appears that, sometime in 774 or 775, planet Earth was hit by a short but strong burst of gamma rays, one of the most powerful forms of energy known.  The evidence comes in the form radioactive isotopes formed in the atmosphere as a consequence of the gamma ray burst.  They include a radioactive form of beryllium (10Be, if you’re curious) found at higher concentrations in Antarctica, as well as carbon-14 (14C, the same isotope of carbon that makes carbon-dating possible) in tree rings across Europe, North America, and Japan.  It’s the 14C from the Japanese tree rings that permitted precise dating of the radiation accumulation to 774-775.  After this sudden radiation spike, which was 10-20 times greater than our normal levels of background radiation, radiation levels quickly returned to normal globally.  While elevated, these levels of radiation were still too low to have a detrimental effect on life.  But, ever since this event was first reported fifteen years ago (and definitively confirmed last year), scientists have wondered what could have caused it.  Given the global distribution of the radiation, and the fact that the radiation had to be formed when high-energy particles reacted with our atmosphere, they looked to outer space for answers.

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Down in the Valley

With blistering days, frigid nights, and parched features, Mercury has long suffered in sun-scorched obscurity.  Ancient astronomers strained to observe the diminutive orb through the sun’s glare.  Their modern counterparts were tempted more by the terrestrial (“rocky”) planets closer to home, peering through Venus’ toxic clouds or scouring Mars for signs of life.  Visits to Mercury by spacecraft long proved elusive, as its swift and close orbit of the sun necessitated risky maneuvers and high fuel consumption.  It was not until 1974 that NASA’s Mariner 10 spacecraft revealed the planet’s pockmarked surface of impact craters, volcanic plains, and giant escarpments.  With apparently little else to offer, astronomers released Mercury back to its sun-drenched procession.

But in the following decades, interest in Mercury reignited as new observations challenged the planet’s desolate reputation.  Evidence emerged that Mercury’s interior may have shrunk.  Radio telescopes unexpectedly hinted that its poles contain water ice.  Clearly, the planet harbors secrets, and in 1998 NASA unveiled a new Mercury mission to investigate them.  Launched in 2004, the MESSENGER spacecraft (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) entered orbit of its target nearly two years ago and began its scientific mission.  Since then, data have poured in on Mercury’s magnetic field, sparse atmosphere, geology, and interior.

More than meets the eye.

More than meets the eye.

Three papers recently published in Science shed light on one of Mercury’s most peculiar puzzles, rumors of water ice at its poles.  Astrophysicists from NASA’s Goddard Space Flight Center, Johns Hopkins University, and the University of California, Los Angeles used data gathered by two of MESSENGER’s instruments to verify that Mercury’s poles contain water ice, as well as another surprise.  The ice resides literally in the shadows, within deep craters and chasms that are shielded permanently from sunlight at the poles and remain cold enough to keep ice stable for extended periods.  In the coldest pockets, ice is exposed at the surface.  But most of the ice MESSENGER detected is insulated beneath a sheath of dark-colored material.

Unexpectedly, MESSENGER’s data indicate that this dark material could be a layer of carbon-rich organic compounds.  If confirmed, these materials would not be signs of life; organic compounds are present in many non-biological settings, and no life, even in the cold shadows, could long withstand the ultraviolet radiation that pummels Mercury.  But it is surprising that typically fragile organic chemicals could persist on Mercury’s uninviting surface.  Like ice, their time in extreme heat is fleeting.  But these cold sunless depths at Mercury’s poles could be a refuge on a planet where daytime temperatures are hot enough to melt lead.

Water ice and organic chemicals likely arrived on Mercury as stowaways on comets and asteroids.  Surveys have detected organic compounds within comets and asteroids, and the rocky planets were bombarded with these celestial drifters early in the solar system’s history.  On Mercury, most fragile stowaways perished in harsh daytime temperatures.  The ice and organic compounds detected by MESSENGER are likely the lucky cargo that accumulated among the cool, sunless corners of the poles.

On Earth, water and organic compounds transported by ancient asteroids and comets had a happier fate.  This organic soup accumulated on our planet’s hospitable surface and, about three billion years ago, life evolved in its depths.  Thus, MESSENGER’s mission to drag Mercury back out of the shadows also helps astrophysicists and biologists understand why Earth became a sanctuary for life, while Mercury, Venus, and Mars took more hostile paths.  Such comparisons are especially relevant in the search for life-bearing planets around distant stars.  For that quest, astronomers must divine the rare Earth among a multitude of Mercurys.

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

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The Toxic Sex

Women tend to live longer than men.  We see this trend definitively in birth and death records going back centuries, and the pattern may even stretch into ancient human history.  Of course, the sad fact is that the life expectancy at birth of someone in the first world is longer than someone born in the third world, since life expectancy varies greatly worldwide.  But, if you compare men and women in the same country or region, men tend to have a shorter life expectancy than women.  According to the CIA World Factbook, global life expectancy at birth for 2012 was 66.57 years, with a half-century spread separating Chad’s 49.69 years and Monaco’s 89.68 years.  The breakdown of life expectancy by sex is striking and nearly universal in pattern.  Worldwide, men at birth can expect to live an average of 64.52 years while the average for women is 68.76.  This trend holds for nearly every country (except for a handful in the midst of prolonged insurgency or ravaged by the unchecked AIDS epidemic).  Monaco’s men have an average life expectancy at birth of nearly 86 years, while for women it is almost 94 years.  For Chad, male life expectancy at birth is just under 48 years, and for women it is nearly 50.  In the United States, a baby boy has can expect to live an average of just over 76 years, while the outlook is five years higher for girls.  Thus, wherever you’re born in the world, it appears that being a man comes with hazards.

The root causes for the predicted shorter lifespan in males have been difficult to pin down.  Still, it doesn’t take much mining of birth and death records to begin to see the symptoms.  Early in life, males actually outnumber females, but die early on at a higher rate.  At fertilization, there are an estimated 107 male embryos for every 100 females.  This ratio decreases to 105 boys for every 100 girls at birth, indicating that more male fetuses die before birth.  This ratio of boys-to-girls continues to decrease slowly throughout childhood, teenage years, and into early adulthood, until roughly age 25.  At that age, women begin to outnumber men, and the trend gets more pronounced as the decades drag on.  In the United States, an estimated 85% of centenarians are women.

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Panda-monium

Do I get a grade for recess?

“Yes, but I excel at recess.”

In their hilarious book The Animal Review: the Genius, Mediocrity, and Breathtaking Stupidity that is Nature, authors Jacob Lentz and Steve Nash assign grades to selected members of the animal kingdom. Great white sharks (“Nature’s perfect killing machines”) get an A+, even though they make “terrible pets.” Owls earn a sold B+ for being “a clairvoyant to the devil.” The giant panda, however, earns a solid failing grade. From its slovenly ways to its slow reproductive cycle, Lentz and Nash playfully assert that the giant panda is so inept that it is simply ill-suited for this world, and doesn’t even appear willing to raise a paw to save itself. With less than 1,600 giant pandas left in the wild, they ponder, “Maybe Nature is trying to give them the hint that they need to go the way of the dodo, and maybe we should spend our time on a species that at least wants to survive.” Though tongue-in-cheek, their message strikes a chord. As a species, the giant panda is in trouble. Shrinking habitat, encroachment by meddlesome humans, dwindling numbers, the ever-present need for vast amounts of food, and a rather slow and ham-fisted approach to reproduction all conspire to make maintaining the giant panda’s population, diversity, and natural lifestyle quite the challenge. The giant panda is not alone in this unique collision of dire circumstances. The almost certainly-doomed polar bear faces a rapidly warming Arctic Ocean, shrinking sea ice, and near starvation, thanks largely to human-induced global climate change. Yet it is the giant panda that zoos across the globe claw to obtain from the Chinese government, spending millions for a breeding pair on loan for ten years. Why does the panda get so much of our attention? And why does it appear that the giant panda is so difficult to save? There are no easy answers to these questions. But to begin to understand the multitude of issues surrounding this reclusive species, we must first delve into the giant panda itself, its home, its history, and its complex relationship with those pesky humans.
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Destination Unknown

Life on Earth evolves (changes) in response to a variety natural forces.  These forces that can drive long-term evolution in species are numerous (and still being worked out by biologists).  For the record, the most well-known and controversial of them is natural selection, trumpeted to fame and infamy in the 19th century by a British naturalist from Shropshire named Charles Robert Darwin.

Many biologists study evolution directly, thinking constantly about natural selection (and other evolutionary forces) and how these forces can shape a population, a species, or an entire ecosystem over many generations.  However, there is another evolutionary force afoot that (in this scientist’s opinion) is rarely discussed within earshot of the general public: us.  Human beings (Homo sapiens).  After all, we affect life on this planet.  Think about all we can do, and have done, in our short history.  With big brains, opposable thumbs, and dashing good looks, humankind has done much: felled forests, sowed crops, drained swamps, built and bombed cities, mowed the grass, trimmed the hedge, obliterated both smallpox and the dodo, migrated to nearly all of the habitable landmasses, and (to my delight) also found time to domesticate the cat.  Just five hours ago, I got my annual influenza vaccine.  So, of course our presence on Earth, equipped with modern technology and in numbers exceeding 7 billion, affects how life evolves on Earth.  It’s a phenomenon that’s easy to fathom once you start fathoming.  But, the details (exactly how we affect the evolution of other lifeforms) have not yet been precisely worked out.

Today, in a ritual perusal of scientific articles, I stumbled upon three studies illustrating new ways in which human beings are affecting the evolution life on Earth.  All three are rather small in scope.  Two studies from Canadian research teams investigate the role of human activity on large species of deer.  The third study concerns a virus that infects chickens.  But, in all three cases, the results are clear: humans are influencing evolution in other organisms.

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