Letters

Thanks for the support As a high school teacher, I have had many students who have heard about the global cooling scare of the 1970s, and these students hold on to those ideas even in the face of overwhelming evidence to suggest that the current warming trend is real. Until I read Sid Perkins’ article “Cooling climate ‘consensus’ of 1970s never was” (SN: 10/25/08, p. 5), I have never had a strong argument to address that concern. There may be only a few global warming critics among scientists, but policy is so often dictated by the court of popular opinion. I am quite glad that Thomas Peterson is doing this work. Jon L. Nauert, Mount Vernon, Wash.

---

First thing first I was intrigued by the ideas discussed in Bruce Bower’s “Body in Mind” article (SN: 10/25/08, p. 24) since I have long felt that there is an overemphasis on algorithms in efforts to create artificial intelligence. I remember arguing with one of Stephen Hawking’s students in Cambridge in 1978 that sensors and actuators are essential to intelligence, artificial or otherwise. Antonio Damasio makes a persuasive case for the inseparability of emotion and reason in his 1994 book Descartes’ Error: Emotion, Reason and the Human Brain. And as aptly summarized by the actor who plays Dr. Maurice Bucke in John Kent Harrisons’ 1990 movie Beautiful Dreamers: “Feeling precedes thinking.” Peter Eisenhardt, Altadena, Calif.

---

Waves pass through Regarding “Solid evidence about Earth’s core” (SN: 9/13/08, p. 14): If Earth has a solid inner core but a liquid outer core, then any direction you look at it, the shear waves have to go through some liquid outer core before they get to the solid inner core. So how do they get through the molten outer core? Tom Turner, Newport, R.I.

When shear waves travel down through the mantle and reach the liquid outer core, some of their energy is converted into pressure waves (which can travel through liquid, unlike shear waves). When those pressure waves reach the solid inner core, some of their energy is converted back into shear waves. Once these vibrations reach the other side of the solid inner core, some of their energy is reconverted into pressure waves that rise through the liquid outer core. Finally, when these waves reach the mantle, some of their energy is again converted to shear waves that then spread and can be detected by seismometers at Earth’s surface.

Each of these conversions—four, count ’em!—is relatively inefficient, leaving little energy in the particular vibrations that the scientists needed to identify in order to bolster their theory. —Sid Perkins

---

Colliding planets

“Impact may have scarred Mars” (SN: 7/19/08, p. 10) interested me. In the article, Francis Nimmo of the University of California, Santa Cruz says that “something big smacked into Mars and stripped half the crust off the planet.” I also understand that the current theory of the formation of the moon suggests that a Mars-sized object sideswiped the Earth.

I know nothing about celestial mechanics, but is there any way that the Earth and Mars could have collided? The impact on Mars might have been smaller if it had formed further away from the sun and thus had cooled and solidified more by the time of the impact.
Dick Smith, Kingsland, Texas

Planetary scientists don’t believe the Earth and Mars could have collided, given their current orbits and where they would have been located in the early solar system. —Ron Cowen