by Catherine Hudson Tuesday, June 14, 2016
“NOVA,” the weekly prime-time science series that airs on PBS, is known for producing high-quality TV documentaries on subjects ranging from espionage and the military to ancient civilizations and nature. Naturally, much “NOVA” programming touches on topics in geoscience, so we decided to review several recent hour-long episodes that might be of particular interest to our readers. To find out about upcoming broadcasts or watch episodes online, visit http://www.pbs.org/wgbh/nova/.
“Life’s Rocky Start”
What roles did rocks and minerals play in the emergence and evolution of life on Earth? That’s the key question that mineralogist Robert Hazen of the Carnegie Institution for Science in Washington, D.C., attempts to answer in “Life’s Rocky Start."
During the show, Hazen travels the world, from the markets of Morocco to the Australian Outback, looking for meteorites, rocks and minerals that might hold clues to the planet’s earliest life forms. Mixed in with footage from field excursions and dialog among Hazen and fellow geoscientists also on the hunt for such clues, he describes the global picture of how the geological and environmental backdrop on Earth changed over time.
Hazen sets the discussion of geology’s impacts on early biology in the context of a color-coded scheme of six stages of Earth’s history. “Black Earth” defines the earliest time on our planet, when it was initially molten and then cooled and was covered in black basalt. “Gray Earth” occurred when granite first formed and continents began to appear. “Blue Earth” represents the appearance of water at the surface. “Red Earth” came about as early oxygen-producing, ocean-dwelling microbes oxidized large amounts of iron in seawater, which then precipitated into massive rust-colored iron deposits on the seafloor. “White Earth” refers to the time when continents broke apart and more advanced organisms, such as trilobites, evolved. And “Green Earth” is the vegetated planet we live on today.
Overall, “Life’s Rocky Start” is both entertaining and educational, a balance that is a challenge for documentaries to achieve. Rock enthusiasts and novices alike are sure to enjoy the light tone and easy-to-follow material and pace. At the very least, it presents a fresh perspective on Earth history and how everything, both living and inanimate, is connected.
The episode “Himalayan Megaquake” opens with raw footage of the earthquake that violently shook Nepal on April 25, 2015. Buildings collapsed and people ran into the streets in terror as others were buried in the rubble of collapsed buildings. The earthquake shaking lasted about a minute, and in the end, more than 8,000 people were killed and more than 21,000 injured.
As soon as the megaquake hit, geologist Roger Bilham, geophysicist John Elliot, and other geoscientists sprang to action, analyzing what had happened and where damage occurred. They also began thinking about when the next major earthquake might strike and how people living in the danger zone could prepare.
The documentary presents eyewitness footage and interviews from the disaster, and covers what is known so far about the science behind the quake, touching on the underlying causes of the main magnitude-7.8 event — as well as the aftershocks, which included a damaging magnitude-7.3 quake in May 2015 that Bilham experienced, on film, during a taxi ride.
The Himalayan Mountains were created by the collision of the Indo-Australian and Eurasian tectonic plates, which continues today. Stress builds up along faults beneath the mountains; earthquakes occur when portions of this stress are released suddenly. The megaquake that hit Nepal was caused by stress that had accumulated since 1833, when the last major earthquake occurred in the area. But, according to geoscientists, the 2015 quake should have been much larger, releasing more stress than it did. This assessment suggests that another megaquake could loom on the horizon for Nepal, perhaps to the west where stress wasn’t released. Just when it will occur, though, is unknown.
“Himalayan Megaquake” is a not-so-subtle reminder that earthquakes can strike at any time and that preparation is key. The episode, with its stories of families near the epicenter and survivors on Mount Everest, as well as those who were not so lucky, packs an emotional punch that viewers won’t soon forget.
“Sinkholes — Buried Alive”
Sinkholes are a constant threat in certain areas of the world: The ground suddenly collapses, pulling whatever is on the surface — everything from trees and cars to houses and, yes, people — into underground chasms. Though they may seem to occur randomly and without warning, the episode “Sinkholes — Buried Alive” explains how these natural phenomena form and offers clues people can look for to help steer clear of them.
Twenty percent of Earth’s land surface, according to the program, is made up of the sort of soluble rocks that compose karst terrain, a landscape where caverns, caves and sinkholes commonly form. This equates to “millions of acres in scores of countries.”
We learn that Florida is riddled with karst sinkholes, for example. There, much of the rock underfoot is limestone, which is easily eroded by acidic rain and groundwater. As rock erodes, large underground cavities, which often can’t be seen from the surface, can form. Over time, dirt and rock above such caverns may slump, and when the cavern is large enough, the land surface may collapse.
Elsewhere, human activity can contribute to the formation of sinkholes. In Louisiana, the ground gave way in 2012 above an underground salt dome that had been mined by pumping water through the ground to dissolve the salt. The hole that formed swallowed trees, burped methane and forced the evacuation of the residents of nearby Bayou Corne.
“Sinkholes — Buried Alive” offers a riveting, frightening look into the science and repercussions of these subterranean hazards. It describes typical signs that warn that Earth’s surface could give way, including cracking, tilting and sagging of the ground and buildings. Even knowing what to look out for, after watching the footage, you may think twice about relocating to an area with the ingredients for sinkholes.
A separate review of the recent three-part “NOVA” series, “Making North America,” can be found here.
___*Update (7/15/16, 3:20 pm EDT) ___The date of the magnitude-7.8 Gorkha earthquake that struck Nepal was previously given as April 15, 2015. The text has been corrected to note that this earthquake occurred on April 25, 2015.
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