Ask Mr. Science
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This dynamic earth:
Volcanos, earthquakes and plate tectonics

This one is about earthquakes and volcanos, which then leads into plate tectonics. First, most of the interior of the earth is liquid, and the what we think of as the solid earth is just a thin crust on the outside. For your typical classroom globe, this amounts only to the thickness of a penny or so. The liquid interior churns around as it heated from the inside, and slowly cools on the outside, and this drags sections of the crust this way and that. Most volcanos and earthquakes occur at plate boundaries. I point out the 'Ring of Fire', since part of it lies to the west of here.

Plenty of local volcanism right here: I can see the remnants of the (dormant) Jemez supervolcano from my window, and I picked up some tuff and some basalt to show, as well as obsidian from elsewhere. I played the movies of continental drift, both past and future (links below). A detail of local interest is in this video at ~84 Million years ago, when New Mexico was at the edge of an inland sea. Carlsbad caverns sit in strata that were laid down on the bottom of that sea.

What if the earth were smaller? All we have to do is look in the neighborhood, to mars or the moon. Mars is a little smaller than the earth, and the moon even smaller. Smaller objects cool faster: the moon is frozen solid already. Mars also cooled off too much to have a liquid interior that would support plate tectonics.

Why should we care about plate tectonics? - after all, if the earth turned solid, there would be no more earthquakes, no more volcanoes. However, after a while, all the carbon would end up on the ocean floor, and without the availability of carbon, all life on earth would be slowly starved and come to an end - not good I'd say. Also, the moving liquid iron generates the earth's magnetic field, which shields us from dangerous radiation from space. Not only would this radiation make us sick, it would also slowly blast away the atmosphere. Better keep those plates going.

Here is a simple demo to show the size/cooling effect: I brought 3 rocks: large, medium, small. They were in a bowl with hot water, so that they all started at the same temperature. Then I set the kitchen timer running, and quickly took the rocks out and placed them on the cutting board. With the little green IR thermometer (here's an example), one student read the temperatures, and another wrote them on the board, once every few (~3) minutes.It becomes clear very quickly that the small rock cools off to room temperature very quickly, the big rock very slowly and the middle rock in between.

One year, I was asked why sparks from sparklers do not burn you. It is because they are so small that they cool off in a fraction of a second.

  Plate tectonics and continental drift:

  Volcanos:

  Earthquakes:

1998
 

Margins of error

Margins of error are an important concept in experimental science. This morning at breakfast there was this article on the front page of the Santa Fe New Mexican, showing the results of a poll taken in the race for the 3rd congressional district. It showed Udall with 42%, Redmond 35%, Miller 8%, undecided 15%.
If the election were held today, I asked the kids, who would win? This was a great question, which led to a number of topics. First of all, what (more) 15 Sep 98
 

How many stars are there in the universe?

I don't have a copy of Carl Sagans book to look up how many billions and billions he thought there were, but here's my guess: Just this week there was a nice article in Scientific American (Oct 98) on our own galaxy and its close neighbors. There I found the estimated number of stars in our own galaxy: about one trillion. The next thing to find out is how many galaxies are there in the universe? For that I went to the Hubble Space Telescope. In 1995, Hubble made a set of observations called the 'Hubble Deep Field'. Basically it stared a tiny patch of the sky which contained no foreground stars or dust clouds, and made an exposure so long that the faintest, furthest galaxies showed up. The size of the field was the size of the period at the end of this sentence, when seen at reading distance. If I assume the dot is 1/2x1/2mm, and reading distance 50cm, it would take about "100%" height=5 000 such fields to cover the whole sky. I believe there are 1000-2000 galaxies in the HDF picture. So my guess for the number of stars in the universe is equal to the number of galaxies in the HDF, times the number of HDF's on the sky, times the number of stars per typical galaxy, or 1500 x 500 000 x 1000 000 000 000 is 750000000000000000000 stars, or 10**21 when rounded up, which is a sextillion start. [We talked about how you form the names of big numbers like that].
Are all these stars sprinkled randomly through space? This is similar to asking if people are distributed randomly on the surface of the earth. People live in small groups in houses, houses are strung together along streets; streets cluster to make towns and cities, and cities can be mostly found along coastlines and rivers. There are vast spaces (oceans, deserts) where hardly a person can be found. Stars similarly congregate: our sun is grouped together with many others in an arm of a spiral-arm galaxy, several arms make up the galaxy; our galaxy is a member of a local group of galaxies, which in turn is a member of the local galaxy supercluster. These clusters can be found along ribbons and sheets of other clusters, and so on up to the largest scales at which we have been able to look. In between the ribbons, sheets and walls of galaxies, there are vast volumes in which hardly a star can be found. be found.


22 Sep 98
 

How come people and dogs live longer

than they did 100 years ago? I don't know about dogs (yet), but if you look at the links below, it is certainly true for humans over the last centuries. Check out Japan (83 for women), Sub-Saharan Africa (50), the middle ages (31), and the last 100 years in Estonia. Increases in life expectancy is due to sanitation mostly, and then primary care medicine. The graph on the top right (stolen from one of the links below), shows an interesting trend: although your chances at birth are getting better and better, the maximum age has not risen much at all. The maximum life span of humans seems to be pretty much fixed, but more and more people are getting up there.

I could not find much about dogs, but the part about medicine should hold true for dogs too.

Are things getting better for horses too? You'd think that continuous advances in training, medicine and careful breeding would produce ever faster race horses. This seems to be true if you look at short-distance races, where records regularly get broken. However, for longer races this is not true. Why? Nobody knows. (SciAm xx 1991).





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