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The Privileged Planet

Guillermo Gonzalez and Jay Richards

So far the talks have been very complementary to what we're going to say and in fact, they lead into some of our material very nicely. First of all let me just start off by saying that we're not going to discuss cosmological issues. We're going to get far away from the Planck era and come to the nearby universe and discuss some local astronomical phenomena that can be quantified empirically. This talk will be entirely based on empirical observational astronomy evidence. Here's our basic thesis: we'll present evidence to show that the degree of measurability of the universe correlates with the degree of habitability over many decades and size and time scales, it's an empirical argument. We also claim that our habitable environment is an exceptional compromise of diverse and sometimes conflicting conditions for measurability ranging from cosmology and galactic astronomy to geophysics. We are not however arguing that every condition for measurability is individually and uniquely optimized for earth's surface. And so I'm going to try to present this case. Unfortunately this really requires about two hours of proper development because we have two separate issues that we are joining. We have an issue of the habitability of a place in the universe or life and we have a second issue and that is the ability to do measurements of the universe and to measure the laws of nature and determine them. Again it was very nice to have Polkinghorne discuss some of the requirements for doing science, and also Hodgson this morning discuss the minimum requirements for science. Well, one of these minimum requirements is actually the ability to measure the universe, that's often taken for granted by scientists, but in fact it's something that could have easily been otherwise. And most people don't realize just how optimized our environment is from measuring the most diverse aspects of the universe. So that's what we'll discuss.

So here's a brief outline of my talk. So first, very briefly define what I mean by habitable, and of course I can't give you every detail so I'm just going to point you to some resources. Secondly, I'll discuss how I first came upon this correlation. First of all let me tell you I didn't set out to find this correlation between habitability and measurability. I just stumbled upon it completely by accident. And that first example is solar eclipses. And then I’m going to give more specific examples that I encountered after I discovered this correlation of eclipses and I found in fact, this is a general property of the universe. And so, there are five different specific examples discussed all relating to the solar system. If I had more time I would also discuss other areas in astrophysics where it appears that this correlation holds, stars, our place in the Milky Way, and finally our time in the universe. But I’ll have to leave that for another talk.

So, what do I mean by a habitable planet? First of all, since the idea of measurement is really only meaningful with complex conscious beings like ourselves, what I mean by life from now on is complex conscious life, something like ourselves. And in fact, I can make more constraints on that, aerobic or oxygen breathing life. And there are also some very basic requirements that you

Seattle Pacific University Transcriptions 2 can really say with certainty are required even for simple life. In fact Polkinghorne alluded to that in his talk. And a few of the other talks, carbon was mentioned. And the remarkable "coincidence" that you have this nuclear energy resonance in the nucleus of the carbon atom that is at just the right place to allow stars to create carbon in high abundance. but that's not the end of the story actually, you need to have it fine tuned both on the lower end of the resonance and at the higher end on the order of about 1% so you can have roughly equal numbers of carbon and oxygen in the universe. If you are far from that resonance one side or the other, either you'd have all carbon and no oxygen or oxygen and no carbon. We live in a universe with roughly equal amounts of carbon and oxygen. And so that's the whole story. So it's even more remarkable than Polkinghorne remarked. And the reason carbon and oxygen are particularly important for life is because first of all carbon is really the only atom you can build life on. Now there have been science fiction stories about silicon and other things, I don't have time to get into that so I'm just going to point you in a direction where you can find very nice information on this. The Anthropic Cosmological Principle by Barrow Tipler, Nature's Destiny by Michael Denton, I think there are copies of this book up there actually, and finally Worlds Without End by John Lewis who's a planetary scientist. And also water is another important requirement. You may not realize this but water, which is such a common compound in the universe, is in fact, quite extraordinary in its properties. And again I refer you to these references to learn just how extraordinary water is as the universal solvent for life. Water contains oxygen and hydrogen and that's where carbon and oxygen come in their importance. Carbon and oxygen come in as the bare minimum requirements for the building blocks of life, any conceivable kind of life in the universe. And many scientists are now coming to accept this. Finally, a terrestrial like planet and a circumstellar habitable zone is required to maintain liquid water. This is a concept that was developed over forty years ago and has been refined over the years by many scientists such as James Casting in Pennsylvania and other astrobiologists and it continues to be refined. You can't just have a planet at any orbit at any place in the solar system to maintain liquid waters stably for long periods of time on the surface. Finally, there is an idea that I am developing with my colleagues, Don Brownlee and Peter Ward at the University of Washington, called the galactic habitable zone. It's somewhat analogous to the circumstellar habitable zone around stars, but it takes into account long term after physical processes such as the production of the elements in supernovas, the position in the galaxy and the dynamics in the galaxy etcetera. If you want to see some details on this, you can find our paper on the web, it's called, The Galactic Habitable Zone on the Astro PH Archive, for those of you who know about that. And there's a very brief sort of lay level description in the book, Rare Earth by Don Brownlee and Peter Ward, but that's a concept we're continuing to work on. And finally, the other way that you can discuss or figure out what the requirements for life is to appeal to the anthropic principle in an empirical sense, not the cosmological sense, but the local astronomical sense in that if we compare the sun and the solar system and its properties to other stars and other planetary systems, then we see that the sun is quite different in one particular property. Then we can infer that particular property is an important property for habitability. So it's a way for at least suggesting possible parameters of

Seattle Pacific University Transcriptions 3 the sun or the solar system that are important for habitability and then you can continue to pursue that through further research. And I'm doing some work in that area too, so there's a reference I provide there. This is literally just the background for what I mean by habitable. I guess complex life, conscious life based on carbon and water and about thirty other chemical elements.

Okay so I grew up as an amateur astronomer so I've always been fascinated by eclipses, solar eclipses, lunar eclipses. I finally got to see, in India in 1995, a total eclipse of the sun. And I was inspired to write a research paper after that comparing the properties or the requirements for eclipses as viewed from the surface of the earth compared to other planets in the solar system. So of course, I'm sure all of you know how eclipses are produced, right? You need three bodies in a straight line in space, a luminous light source, an eclipsing body, and finally an observer platform all in a straight line in space. And they have to be constrained such that the eclipsing body, in our case the moon, it has a slightly larger apparent size than the eclipsed luminous body, therefore, blocking the entire light from the photosphere. Here is a picture from the 1995 eclipse and I superimposed the disk of the sun which you cannot see in an eclipse, but just to show you the very close relative sizes between the sun and the moon during an eclipse and also the very nice circularity of the lunar profile. You can see the solar corona during an eclipse and shown in red on either side, you can see the range of the apparent size of the moon relative to the sun in modern times. And notice that the average size is almost exactly the same. The moon's disk is almost exactly the same as the solar disk, the average size over that range. So that's interesting, we can see eclipses on the earth, so what? Well, lots of people are inspired by eclipses and that's one interesting aspect of it, people feel deep inspiration from it. But there is more significance than that. So of over 70 natural satellites or moons in the solar system that we know of today, actually the moon produces by far the best eclipses from any planetary surface in the solar system. So I've plotted here, to put things in proper context, you always want to compare the earth to other environments, so I've plotted the ratio of the apparent size of the sun to the moon on the horizontal axis and on the vertical axis, I've just put different planets with their moons. So that vertical dotted line shows you unity, ratio of unity where the apparent size of the moon is equal to the apparent size of the sun. And you can see that the moon crosses that line exactly in the middle, with a small range. And it's a logarithmic scale, so things may look a little closer than they really are. Things are really scattered quite a lot in that diagram. So if you look at that graph, there's only one other moon that crosses that median unity line and that's the moon Prometheus around Saturn, a rather small potato shaped moon that has eclipses lasting less than one second. There are several other reasons that the moon produces the best eclipses from the earth. For example, the sun has the largest apparent size of any, from any planet with a moon. The moon has an almost perfectly round profile in the sky, so it produces a very nice match to the extremely round profile of the sun. That's not yet the end of the story.

I also did a calculation showing how things change in time and if you take into account the recession of the moon from the earth from the transfer of angular momentum from the earth's rotation to the moon's orbit and also the evolution of the sun’s size over time due to ordinary

Seattle Pacific University Transcriptions 4 stellar evolution, you find that we're not going to continue observing eclipses forever. In fact, they're only going to last another 250 million years. These effects go against each other, right? The sun swelling in size and the moon moving away are both acting against each other. So in only 250 million years we will cease to be able to observe total eclipses from the earth. By the way, this happens to be close to the best estimates for the predicted lifetime of the biosphere for advanced life on the earth, roughly 300 million years. I discussed the technical aspects of this, again, in a paper in Astronomy and Geophysics in 1999. So the most basic requirements of producing solar eclipses are also strongly constrained by habitability requirements, and this is something that I just found by accident. In particular, the spectral type of the star in setting the size of the circumstellar habitable zone and the size to the distance of the moon in stabilizing the earth’s obliquity. The time scale for the moon to migrate to the present location is a similar time scale for the appearance of complex life. In other words, there's another issue here that I haven't gotten to yet and that's the importance of the moon for habitability, this was just discovered in 1993. The moon stabilizes the obliquity of the earth's rotation axis and that's a very important requirement to have complex life on earth. You don't want the temperature to swing wildly all the time because of variations in the tilt of the rotation of the earth. The moon keeps that stable to within plus or minus 1.3 degrees. So the moon has actually an important role to play in maintaining the Earth's climate very stable. And of course where we are in the solar system, i.e. in the circumstellar habitable zone, is set by the properties of the sun. So right here, you have two very important properties, requirements for habitability, namely the distance from the apparent star which is set by its luminosity and astrophysical characteristics, and the rough distance and mass of the moon which determines the stabilization of the earth's rotation axis. These are the two most critical constraints in constraining where you see solar eclipses. So I just found this to be a fascinating coincidence. Namely, the very requirements which are so important for habitability on the earth, happen to be two constraints, the two very constraints that you need to determine if you can see eclipses or not. In other words those habitable places in the universe like the earth, those most habitable places, and I have other reasons for arguing why I think the Earth is close to optimal habitability, will probably also see solar eclipses. Because you have to be a certain distance from that star, and you have to be orbiting a certain kind of star to optimize habitability and it really helps to have a large moon at a certain distance, and so when you put all of these things together, that means aliens, if they exist, probably also see eclipses. I mentioned this at a BBC radio interview that I had in 1999 the day of the European eclipse of 1999, and the interviewer was surprised by this, but found it a fascinating idea, that other aliens would also see eclipses, they'd be more likely to anyway.

So I thought this was an interesting coincidence and I asked myself "is this a typical property of the universe or is this just this one place, this one fluke where it happens that this particular measurable aspect of the universe, i.e. the observability of solar, total eclipses of the sun happens to correlate with habitability? Is it just this one place where this happens?" So it's a simple investigation I set out to do. I think it's the kind of question you have to have a certain openness to address. For example, if you're a naturalist, if you think that there is nothing else but the

Seattle Pacific University Transcriptions 5 particles in the universe without any intent or anything else, you'd probably tend to say, "Oh this is obviously a coincidence, this is obviously a fluke. Why would habitability correlate with measurability?" but because I have a slightly different angle that I'm coming from I was more open to that possibility. Okay, so I decide to start looking at other places in the universe that we know a lot about, where the science is relatively well developed. So I started with the earth sciences at the surface of the earth and the field of paleoclimatology, the reconstruction of the ancient climate is a very interesting one and it's one that has a great deal of activity going on today. In particular sedimentary and layer deposits contain a lot of information that we make use of to reconstruct the ancient climate of the earth, but you can’t just get sedimentary or growth processes anywhere, there are certain basic requirements. So let’s go through those four basic requirements. Basic requirements for recording information on the planetary body are one, a layers recording medium with a superimposed time marker, two, the ability to incorporate tracers at service proxies of various environmental prop parameters, three, the preservation of deposit layers until they are recovered by investigators and four, the ability to extract tracers and relate them to environmental parameters. This is very general a definition of the minimum requirements for some kind of a recording medium on a planetary body that records information reliably that can be later extracted. So let me just give you a real world example to put that in a better framework. So the first example, ice cores; ice cores are just the scientist’s laboratory, you might say, for studying ancient ice deposits in the polar regions of the earth. They take a drill rig like the use for looking for oil in different parts of the world, except they put one in say, Antarctica. And they literally take a core of ice going down about two miles in Antarctica or Greenland and it is quite amazing how much information can be recovered d from an ice core. And I've just listed those there: local temperature, precipitation, dessert dust, carbon dioxide, methane, nitrous oxides, various cosmogenic isotopes like beryllium 10 or carbon 14, marine aerosols, volcanic ash, you can see the sunspot cycle and study the Milankovitch cycles. Milankovitch cycles are the astronomical, orbital frequencies, for example, the orbital period of the moon, the precession cycle of the earth moon system, the period of variation of the eccentricity of the earth's orbit. All of these things are encoded in ice. And many people who study this area are really amazed at just how much information is encoded in ice, and not just local information, but global information. The carbon dioxide trapped in air bubbles in ice is global.

You can think of these kinds of recorders, these layer or depositional recorders as analogues to scientific recorders like strip chart recorders. In a strip chart recorder you have a paper running at a constant set rate with some pen marking the signal, it's hooked up to a transducer, and then another pen that is a time marker, has ticks that constant time intervals. We can think of the papers analogous to say the ice in an ice core and the pen recording the signal is some kind of tracer that's in the ice and the time marker is whatever you're using to calibrate the ice time. For example it can be annual deposition layers which you can see in the ice or it could be a calibration with the Milankovitch cycles which we can determine from computer simulations.

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So ice is not the only one so let’s go on to the others. You can also get marine deposits on the ocean floor from sediments just depositing on the ocean floor, I'm not going to go into the details of the things you can determine. You can also have biological growth layer processes that record information. Tree rings, right? The tree rings grow on top of the previous year’s growth, they don't destroy the previous year's growth, they deposit on top of it. Or you have mollusk shells and stromatolites and horn corals. And finally you have the continents which themselves preserve ancient pieces of the oceanic crust, and so we can go back several billion years to study the ancient paleoclimate of the earth. So these are all types of phenomena that occur on the surface of the earth and they're related, in ways that I can't get into with complete detail with the time allotted, to habitability of the earth. And some of these are related very directly to life, some of these in fact are due to life. Like I said, tree rings, and corals and mollusk shells. In fact the marine deposits contain very small microscopic fauna, foraminifera. I didn't say that right. I'll skip that one. They’re microscopic marine fauna whose shells get deposited in the ocean floor and what scientists do is measure the oxygen isotope ratios inside them. As it turns out the oxic isotope ratios are very sensitive function of the ocean temperature where they are deposited from and there are two types. The shallow marine fauna and the benthic, or deep, marine fauna and they give us temperature records of the deep ocean and the shallow ocean. But if it wasn’t for the marine fauna deposited on the marine floor we'd have a much poorer measure of the paleoclimate. So there are many ways in which biological processes directly enhance the ability to reconstruct the ancient climate of the earth and many indirect ways. So, let me go on to a different topic and by the way I'm going to compare this to the other planets later so I can put this in a proper context. I'm not just going to discuss the earth by itself.

So another way of measuring something, actually I forgot to show those plots. Before I go to the next topic, here's just one example of the kinds of very diverse data sets that can be obtained from depositional phenomena on the earth. They include Greenland ice cores or deep water surface of plank tonic fauna temperature reconstructions, Iceland, ice rafted detritus accumulation, for example when icebergs break off the north arctic regions, they melt in the north Atlantic ocean and deposit detritus and so we can actually, we can actually, we construct the amount of grafted ice in the ancient past from the cores in the North Atlantic. There's almost nothing about the ancient climate that you cannot determine from these ancient processes. So I'm not going to discuss these in detail I just wanted you to see the tremendous diversity of different kinds of phenomena that are very clearly and cleanly recorded and recorded one layer on top of the other which is absolutely essential, you don't destroy the previous information but you very gently deposit another layer on top of the previous one. Here's an example of the information that can be reconstructed from Antarctic ice cores, it includes the deuterium isotope variation and that's very directly readable to the local surface temperature and you have other things like oxygen isotope variations which is the second curve down which is relatable to the global ice volume and other things. I'm not going to go through in detail, but we can go back about 400,000 years from the Antarctic ice cores. And we can go back about 100,000 years from the Greenland ice cores. And I guess we'll skip the next graph and go directly to earthquakes.

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Okay so earthquakes are another very useful way of actually getting information about the earth. As you know, earthquakes generate waves, p waves and s waves that travel through the earth and they tell us about the different state of the interior of the earth, whether it's solid or liquid. We can reconstruct the density structure of the earth both gradially and also the inhomogeneities in the earth and we can do this because the tectonic zones in the earth are widely distributed along the plate boundaries and so we get a very nice set of sources of waves going off every once in a while around the earth that pass waves through the earth. And you can think of it as just sampling right? The waves sample the material they go through. And because the continental plate boundaries are widely distributed and because the continents are widely distributed, we have the nearly optimum ability to very quickly measure the earth's interior because the earthquake sources themselves are widely distributed and we can widely distribute that the seismographs are around the world. The reason we have earthquakes is because of plate tectonic activity which moves the plates around and they sometimes jostle quickly and release tension and produce earthquake demonstrated waves but plate tectonic activity itself is a very important requirement for habitably on a planet. It's the central engine that drives the carbon silicate cycle, for example, that buries the carbonates and eventually recycles them through volcanism. And that's a very important process, via surface processes, including life that regulates the global temperature. But one of the benefits of plate tectonics is that it generates earthquakes. And by the way, earthquakes are dangerous, we know why they happen, we just don't know when they happen. If we wanted to we could really avoid almost completely deaths from earthquakes, it's just we decide where we want to live.

So earthquakes are another one of those interesting cases where you have something that allows you to measure some aspect of your environment, but it's also closely tied to habitability. So Earth's atmosphere, this has been noted by many authors before, and in fact, they're quite amazed by it, the fact that the earth’s atmosphere is transparent over the same region that the radiation from the sun peaks in intensity and also the same region where our visual acuity peaks. But it's not just translucent, I have to emphasize that, it's transparent, okay? And those of you, who live in Seattle, know the difference between translucent and transparent. In the winter, our atmosphere in Seattle is translucent, in the summer it's transparent and it makes all the difference in the world for measuring the universe beyond the earth. We wouldn't have astronomy if the earth's atmosphere was not transparent, and as I'll discuss in a minute that's not a guaranteed property of a planetary surface. It also happens to be relatable to habitability in the sense that an atmosphere which is at least partly cloudy but not completely cloudy allows better maintenance of an atmosphere, through, of a climate through feedback mechanisms. If you have a completely cloudy atmosphere you can't have feedback. By variations in cloudiness, if you have a completely clear atmosphere, you also cannot have feedback. And if you want to get into the whole Daisyworld model of Lovelock applies here and the various associated Gaia Hypothesis Models through feedback mechanisms and these are also mediated by biological processes. A particularly interesting example to me is meteorites and this is one that I noticed rather recently and in fact it was brought to my attention by Donald Brownlee who is a meteorite expert here at

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University of Washington. It was only around 1970 that meteoriticist first noticed that, or first admitted, that meteorites actually contained stardust. Meteorites, the primitive meteorites, carbonations chondrites, actually contain pieces, individual pieces of stardust. Grains of dust that were ejected by individual stars that lived before the sun formed. Somehow stardust that formed in the winds of stars and in supernova explosions over the past history of the universe mixed throughout the galaxy, throughout the intersolar medium and somehow got incorporated into HI molecular cloud that eventually collapsed to form our solar system. The formation of the solar system was a very violent process. It was a very homogenizing process. Things were intensely heated and mixed and melted. The meteorites we get today are from the asteroid belt, that's where they all come from and they are in various states of preservation. Many of them have been homogenized by being in larger parent bodies where there is enough heat for the whole thing to melt. A few of them come from very primitive bodies that did not melt throughout. And by the way they get transferred to the earth today through their chaotic motion and to the so called Kirkwood gaps in the asteroid belt which are resonances with the orbit of Jupiter and their orbits get pumped in the high eccentricities which eventually send them to the earth and we pick them up as meteorites and Antarctica. In fact, they're delivered to our backyard literally, so you can hold in your hand a two pound rock, a meteorite, and literally inside that rock are thousands of individual stardust grains from individual stars delivered to your doorstep literally and it forms a completely new branch of astrophysics, one which is very complementary by the way to stellar spectroscopy, which is my area of specialty. Stellar spectroscopy gives you information on atomic abundances in stellar atmospheres and relatively little information on isotopic abundances in stellar atmospheres. You can get some information, for example, on carbon 12 to 13 ratios in stars from looking at CN molecule. The isotopic shift for molecules is much larger than it is for individual atoms; that's how it can do it in stars. But for meteorites all you have are isotope ratios. So it's very complementary to stellar spectroscopy and we can link the two with a few ratios that are measurable in both sets of stars, so if you show the first page of that paper with the nice color graph on it... here’s just a very recent paper presented at the Lunar Planetary Science Conference, number 32 earlier this year by Ernst Zenner and colleagues. Ernst Zenner is the world’s expert on the study of the isotope ratios in individual stardust grains in meteorites. Showing you that there is very active research in this area today. This first plot is just a theoretical plot of the expected loci of the silicon isotope ratios on this isotope, isotope plot where you're plotting the ratio of silicone 29 to silicone 28 versus ratio of silicon 30 to silicon 28. On the bottom and so you have a 2 d plot where you can separate out various effects due first of all galactica equevolution which is the 45 degree angle line with little ellipses and then individual nucleosynthesis processing individual red giants which is this line off to the side. And on the next page there, I have real data, real individual interstellar stardust grains where they measure the isotope ratios of individual grains and figure out some information on the past history, galactical equevolution history of these grains and individual processes, individual stars that alter the isotope ratios. This is just an enormously important source of information to learn about the nucleosynthesis history of the galaxy again that is complementary to stellar

Seattle Pacific University Transcriptions 9 spectroscopy and again stellar spectroscopy is only possible because we have a transparent atmosphere. So what does this have to do with habitability though? As it turns out about 99.9 percent of the mass o the asteroid belt has been lost, mostly in the early history of the solar system through perturbations by larger protoplanetary embryos that were once in that region and eventually scattered by Jupiter. The fact that any of it remains is extremely sensitive to the timing of Jupiter’s formation. So if you had Jupiter forming at a slightly different time perhaps it would not have scattered away those early embryos in the asteroid region and they would have completely decimated the asteroid belt. See as soon as you incorporate a primitive carbonaceous chondrites material into a planetary body it will be homogenized and the larger the body the more that rock will be homogenized. So the key is to avoid getting this primitive material incorporated into a large planetary body. And so that's why it's important to have these smallish asteroids around that preserve almost completely the original material of these interstellar dust grains.

And Jupiter is very important for habitability and for the reasons shown by George Weatherall, Jupiter shields the earth from too many comet impacts through its gravitational perturbations and Jupiter itself has to have very specifically set parameters, if it were a little bit closer to the intersolar system it would have perturbed the inner planets too much. It's important that we preserve a circular orbit. For the earth to preserve a circular orbit, Jupiter can't be too close to us, Jupiter can't be too massive, Jupiter can't have too eccentric an orbit. And by the way, almost all those extra solar planets they're finding around other stars beyond our orbit of two weeks are all highly eccentric in their orbits so they wouldn't allow for planets to remain in stable circular orbits for a long time. That shows you how different our solar system is from others by the way.

So, I'd like to compare our earth to, very briefly, just to some other planets in the solar system. So, the Earth achieves a rather critical balance between fluid processes, required to both record and preserve information. You have fluid activity or fluid dynamic or motion in other planetary bodies, Jupiter’s atmosphere is extremely dynamic, very complex, but it doesn't encode information, right? The comet Shoemaker Levy 9 impacts that occurred in Jupiter’s atmosphere in July of 1994 are no longer there, they are erased, there's no record of them. Whereas impact records on planet earth, to a solid planetary body are preserved, like the earth or the moon or mars. The atmosphere of the gas giants also wouldn't allow for any observers to see, in fact there is no solid surface for an observer to live on in a gas giant atmosphere. Mercury and the moon have no weather so they can't record on their surfaces, yet of course that gives the advantage of having a clearer view of the distant universe. And this is where the idea of our constrain optimization of the earth system comes in. Namely, we're not claiming that the earth is absolutely optimum in every aspect for measurability. But like a laptop is optimized in a constrained way, each component of a laptop is optimized in a constrained way to match the other components of the other requirements, for example requirements for small size, requirements for a large screen etcetera. But if you had each of those components by themselves, perhaps you would optimize them a little better. NJ is going to talk a little bit more about that

Seattle Pacific University Transcriptions 10 later. So the earth leads to very remarkably diverse collection of the ability to measure the universe, in fact having a transparent atmosphere is almost as good has having no atmosphere in many respects. But it is infinitely better than having a translucent atmosphere. There’s a big difference between having a transparent atmosphere and having a translucent one, but not such a big difference between not having an atmosphere and having an atmosphere. Especially if most of the radiation produced by stars is emitted in that narrow window that is transmitted by the earth's atmosphere. The smaller planets do not have continuous geologic activity, many of them are too small to maintain plate tectonic activity and so they will not generate very many earthquakes. So you can’t map their interiors very well. The moon for example is the only other planetary body that has hat its interior body mapped. The Apollo astronauts put four seismographs on the surface in 1969, they operated for 8 years and recorded 12,000 events only 81 of those events were useful to reconstruct its interior because they're very weak. They're typically only Richter 3, are three on the Richter scale, or weaker. And the moon's highly fractured crust also scatters seismic waves a great deal which leads to extreme complication in interpreting the seismic data, but we don't have that problem on the earth because we don't have such a highly fractured crust.

So, in summary, the processes that occur on the surface of the earth which record and preserve information relatable to the specific physical quantities over a broad range of time scale. These processes are analogous to data recorders employed by scientists. If you don't like the example of a strip chart recorder then use an ADD converter attached to a laptop, that's still is similar. Real time observation of interterrestrial and extraterrestrial environments is both possible from the surface of the earth, the same processes and physical conditions that optimize habitability on a planetary body also optimize measurability. Unfortunately I can only go into this in the briefest detail, I have many more examples I could have given you where it appears that habitability correlates with measurability, but I'll let Jane discuss the implications of this

Seattle Pacific University Transcriptions