In “A History in Layers,” Jan Zalasiewicz argues that humans' effect on the earth calls for the establishment of a distinct geologic epoch called the Anthropocene.

If humans stay around on the earth for millions of years, naming the present era the Anthropocene will most likely be justified. On the other hand, there is a distinct possibility that we shall succeed in exterminating ourselves within a short period. In that case, the impact of humanity would rather resemble that of the asteroid that killed the dinosaurs. On the geologic timescale, it would be the blink of an eye—short and terrible. Then some other future species will handle the naming issue.

Kongens Lyngby, Denmark


Senior editor Gary Stix reports on the contrast between a growing number of neuroscience Ph.D.s and the progressively reduced number of positions in academic research and asks, “Where Will All the New Neuroscientists Go?” [Advances]. As a psychiatrist, I encourage such Ph.D.s to go to medical school and specialize in psychiatry. Individuals who suffer from mental illness, and those who treat them, are greatly in need of more neuroscientists to help delineate the biological underpinnings of mental disorders and their effective treatments. Because these underpinnings help create the complex human mind—and complete person—we should also reaffirm the critical skills psychiatrists need to understand and communicate effectively with that person. Psychiatry has never been more compelling, and it needs good people.

Corvallis, Ore.


Bill Gifford does not discuss the economic burden that would be created by a substantial increase in healthy life span in “Living to 120.” Many human activities are benign when only a few participate but become problematic when too many do it. Living longer is an affordable indulgence when becoming a centenarian is rare enough that it can be marked by a letter from the British monarch. What happens when 7.4 billion of us aspire to such an age? Although increasing the years of healthy life reduces the costs of health care, the healthy elderly still consume resources.

Stirling, Australia


In “At the Boundary of Knowledge” [Skeptic], Michael Shermer argues that physics disproves, or reduces to the vanishing point, the possibility of paranormal phenomena. Instead of beating the dead horse of scientific atheism, he should have considered a far more amazing current trend that places so-called supernatural phenomena on the same playing field as natural events: in physics and biology, a crisis of knowledge has developed when attempting to account for the fundamental definitions of time, space, matter, energy and life. In a cosmos ruled by dark matter and energy, where no empirical evidence exists about the origin of time, the multiverse is pure conjecture and no one knows how the fundamental physical constants emerged from the big bang, Shermer's stubborn physicalism is not true to the current situation in science.

A growing cadre of investigators has opened the door to a once forbidden subject: consciousness. Until we understand how consciousness comes about, both normal and paranormal events are equally mysterious. Two observers—one claiming to see angels, the other to see nebulae and galaxies—derive their experience from totally unknown processes by which the brain, using ordinary electrochemical activity, produces a 3-D world. Max Planck declared, “All matter originates and exists only by virtue of a force.... We must assume behind this force the existence of a conscious and intelligent Mind. This Mind is the matrix of all matter.” Werner Heisenberg asserted, “The atoms or the elementary particles themselves are not as real [as phenomena in daily life]; they form a world of potentialities or possibilities rather than one of things or facts.”

It's time for Shermer to read these seminal physicists so that instead of relying on a primitive belief that all phenomena come down to the interaction of particles, he gets into the game when it's finally becoming interesting.

University of California, San Diego, School of Medicine

SHERMER REPLIES: The door to the once forbidden subject of consciousness was opened by hard-core natural scientists such as Francis Crick and Christof Koch, who collaborated on models to explain how conscious experiences arise from neural activity without invoking the supernatural. And it is tautologous to assert that conscious experiences are explained by consciousness. How neural processes lead to conscious experiences is becoming understood through the tools of neuroscience, and while the hard problem of explaining consciousness is not yet solved, by no means is it the result of “totally unknown processes.”

As for Planck and Heisenberg: two quotes do not an argument make. Most physicists do not assume a conscious, intelligent mind is behind matter and energy, and the nature of atoms and elementary particles may be a world of potentialities, but at the macro level, where we live, you need only to thrust your fist into a brick wall to refute Chopra's assertions.


In “What to Do with All Those Cassettes” [TechnoFiles], David Pogue describes “the world's VCR and camcorder tapes” as now “rotting in boxes” and encourages readers to digitize them. Pogue shouldn't be so fast to imply that analog media are no longer used at all. I have stacks of videocassettes and audiocassettes—even eight-track tapes. I also have shelves of vinyl LPs, some of which are irreplaceable. And a few weeks ago I wandered into a bookstore (another rarity), and what do I see right inside the doors? A huge display of vinyl LPs and signs touting their advantages.

Mannington, W.V.


“A History in Layers,” by Jan Zalasiewicz, referred to the Holocene starting 11,700 years ago, with glaciers “melting so much they raised sea level globally by 120 meters.” That 120-meter rise specifically occurred between 18,000 and 8,000 years ago, across the transition from the Pleistocene to the Holocene. Additionally, the box entitled “When Did the Anthropocene Begin?” should have specified that plutonium 239 decays into uranium 235 and not implied that plutonium 240 does.


“The Kilogram Makeover,” by Knvul Sheikh [Advances], incorrectly stated that contraction or expansion of the Le Grand K cylinder can alter its mass. Instead molecules could escape from the cylinder in a process called outgassing, which would cause it to lose mass. It could also gain mass from molecules landing on and sticking to its surface. Further, it should have credited the National Institute of Standards and Technology as the source for the statistics in the “By the Numbers” box.

In “A Tale of Two Worlds,” by Mara Hvistendahl, the box by Pamela Ronald entitled “Can We Feed the Planet without Destroying It?” incorrectly said Ronald is a professor emerita at the University of California, Davis. She is an active professor there.