Neanderthals: skilled or unskilled?

Recently, you may have seen images of a rather odd-looking bone carving, made 50,000 years ago by Neanderthals. One of the curious things about Neanderthals is that they have been portrayed as brutes, a sort of dead-end in the line of human evolution, probably wiped out by our ancestors. However, this is somewhat unfair for several reasons, one of which is this bone carving. It involved technology because apparently the bone was scraped and then seemingly boiling or some equivalent heat processing took place. Then two sets of three parallel lines, the sets normal to each other, were carved on it. What does this tell us? First, it appears they had abstract art, but a more interesting question is, did it mean anything more? We shall probably never know.

One thing that has led to the “brute” concept is they did not leave many artifacts, and those they did were stone tools that compared with our “later ancestors” appeared rather crude. But is that assessment fair? The refinement of a stone tool probably depends on the type of stone available. The Neanderthals lived more or less during an ice age, and while everything was not covered with glaciers, the glaciers would have inhibited trade. People had to use what was available. How many of you live in a place where high quality flint for knapping is available? Where I live, the most common rocks available are greywacke, basalt, and maybe some diorite, granodiorite or gabbro. You try making fine stone tools with these raw materials.

Another point, of course, is that while they lived in the “stone age”, most of their tools would actually be made of wood, with limited use of bone, antler and ivory. Stone tools were made because stone was the toughest material they could find, and they hoped to get a sharp edge which would make a useful cutting edge. Most of the wooden items will have long rotted, which is unfortunate, but some isolated items remain, including roughly 40 pieces of modified boxwood, which are interpreted as being used as digging sticks and were preserved in mudstone in Central Italy. These were 170,000 years old. Even older were nine well-preserved wooden spears is a coal mine at Schöningen, from 300,000 years ago. Making these would involve selecting and cutting a useful piece of spruce, shaping a handle, removing the bark (assumed to be done through fire) smoothing the handle with an abrasive stone, and sharpening the point, again with an abrasive stone.

Even more technically advanced, apparently stone objects were attached to wooden handles with a binding agent. The wooden parts have long rotted, but the production can be inferred from the traces of hafting wear and of adhesive material on the stones. Thus Neanderthals made stone-tipped wooden spears, hafted cutting and scraping tools, and they employed a variety of adhesives. Thus they made two different classes of artifacts each comprising at least three components. They were making objects more complex than some recent hunter-gatherers. There is a further point. The items require a number of steps to make them, and they require quite different skills. The better tools would be made quicker if there were different people making the various components, but that would require organization, and ensuring each knew what then others were doing. That involves language. We have also found a pit that contains many bones and tools for cutting meat from them, presumably a butchery where the results of a successful hunt were processed. That involves sharing the work, and presumably the yield. 

We have found graves. They must have endured pain because they invariably have the signs of at least one fracture that healed. To survive such injuries they must have had others care for them. Also found have been sharpened pieces of manganese dioxide, which is soft but very black. Presumably these were crayons, which implies decorating something, the somethings long rotted away. There are Neanderthal cave paintings in SpainFinally, there was jewellery, which largely involved shells and animals’ teeth with holes cut into them. Some shells were pigmented, which means decoration. Which raises the question, could you cut a hole in a tooth with the only available tools being what you made from stone, bone, or whatever is locally available naturally? Finally, there are the ”what were they” artifacts. One is the so-called Neanderthal flute – a 43,000 – 60,000- year-old bear femur with four holes drilled in it. The spacings does not match any carnivore’s tooth spacing, but they do match that of a musical scale, which, as an aside, indicate the use of a minor scale. There is also one carving of a pregnant woman attributed to them.  These guys were cleverer than we give them credit for.

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Could Aliens Know We Are Here?

While an alien could not see us without coming here, why pick here as opposed to all the other stars? We see exoplanets and speculate on whether they could hold life, but how many exoplanets could see our planet, if they held life with technology like ours or a little better? When I wrote the first edition of my ebook “Planetary Formation and Biogenesis” I listed a few techniques to find planets. Then, the most had been found through detecting the wobble of stars through the frequency changes of their line spectra to which a Doppler shift was added. The wobble is caused by the gravity of the planets. Earth would be very difficult to see that way because it is too small. This works best with very large planets very close to stars.

While there are several methods for discovering planets that work occasionally, one is particularly productive, and that is to measure the light intensity coming from the star. If a planet crosses our line of sight, the light dims. Maybe not a lot, but it dims. If you have seen an eclipse of the sun you will get the idea, but if you have seen a transit of Venus or of Mercury you will know the effect is not strong. This is very geometry specific because you have to be able to draw a straight line between your eye, the planet and part of the star and the further the planet is from the star, the smaller the necessary angle. To give an idea of the problem, our planetary system was created more or less on the equatorial plane of the accretion disk that formed the sun, so we should at least see transits of our inner planets, right? Well, not exactly because the various orbits do not lie on one plane. My phrase “more or less” indicates the problem – we have to be exactly edge-on to the plane unless the planet is really close to the star, when geometry lends a hand because the star is so big that something small crossing in front can be seen from wider angles.

Nevertheless, the Kepler telescope has seen many such exoplanets. Interestingly, the Kepler telescope, besides finding a number of stars with multiple planets close to the star has also found a number of stars with only one planet at a good distance from the star. That does not mean there are no other planets; it may mean nothing more than that one is accidentally the only one whose orbital plane lies on our line of sight. The others may, like Venus, be on slightly different planes. When I wrote that ebook, it was obvious that suitable stars were not that common, and since we were looking at stars one at a time over an extended period, not many planets would be discovered. The Kepler telescope changed that because when it came into operation, it could view hundreds of thousands of stars simultaneously.

All of which raises the interesting question, how many aliens, if they had good astronomical techniques, could see us by this method, assuming they looked at our sun? Should we try to remain hidden or not? Can we, if we so desired?

In a recent paper from Nature (594, pp505 – 507 2021) it appears that 1,715 stars within 100 parsecs of the sun (i.e. our “nearest neighbours”) would have been in a position to spot us over the last 5,000 years, while an additional 319 stars will have the opportunity over the next 5,000 years. Stars might look as if they are fixed in position, but actually they are speedily moving, and not all in the same direction. 

Among this set of stars are seven known to have exoplanets, including Ross 128, which could have seen us in the past but no longer, and Teegarden’s star and Trappist-1, which will start to have the opportunity in 29 years and 1642 years respectively. Most of these are Red Dwarfs, and if you accept my analysis in my ebook, then they will not have technological life. The reason is the planets with composition suitable to generate biogenesis will be too close to the star so will be far too hot, and yet probably receive insufficient higher frequency light to drive anything like photosynthesis.

Currently, an Earth transit could be seen from 1402 stars, and this includes 128 G-type stars, like our sun. There are 73 K stars, which may also be suitable to house life. There are also 63 F-type stars. These stars are larger than the sun, from 1.07 to 1.4 times the size, and are much hotter than the sun. Accordingly, they turn out more UV, which might be problematical for life, although the smaller ones may be suitable and the Earth-equivalent planet will be a lot further from the star. However, they are also shorter-lived, so the bigger ones may not have had time. About 2/3 of these stars are in a more restricted transit zone, and could, from geometry, observe an Earth transit for ten hours. So there are a number of stars from which we cannot hide. Ten hours would give a dedicated astronomer with the correct equipment plenty of time to work out we have oxygen and an ozone layer, and that means life must be here.

Another option is to record our radio waves. We have been sending them out for about 100 years, and about 75 of our 1402 stars identified above are within that distance that could give visual confirmation via observing a transit. We cannot hide. However, that does not mean any of those stars could do anything about it. Even if planets around them have life, that does not mean it is technological, and even if it were, that does not mean they can travel through interstellar space. After all, we cannot. Nevertheless, it is an interesting matter to speculate about.

Why Plate Tectonics?

How did plate tectonics start? Why has Earth got them and none of the rocky planets have, at least as far as we know? In my ebook “Planetary Formation and Biogenesis” my explanation as to one of the reasons for why plate tectonics are absent on Mars is that the Martian basaltic mantle appears to have about 17% iron oxide whle Earth has 7 – 11%. This means it cannot make eclogite whereas Earth’s basalt can. Eclogite is a particularly dense silicate and it is only made under serious pressure. 

To see the significance, we have to ask ourselves how plate tectonics works. The core generates hot spots, and hotter mantle material rises and has to push aside other rock, and we get what we call seafloor spreading, although it does not have to be underwater. The African rift valley is an example, in this case a relatively new example where the African plate is dividing, and eventually will have sea between Somalia and the Nubian zone. Similarly, the Icelandic volcanoes are due to “seafloor spreading”. Thus matter coming up pushes the surface plates aside, but then what? On Mars, the cold basalt has nowhere to go so it forms what is called a “stagnant lid”, and heat can only escape through volcanism. On Mars, this resulted in quite significant volcanism about three and a half billion years ago, then this more or less stopped, although not as much as some think because there is evidence of volcanic eruptions around Elysium within the last two million years. The net result is the “lid” gradually gets thicker, and stronger, which means the heat loss of the Martian mantle is actually much less than that of Earth.

On Earth, what happens is that as the basaltic plates get pushed aside, one goes under another, and this is where then eclogite becomes relevant. As the plate goes down, the increased pressure causes the basalt to form eclogite, and because it is denser than its surroundings, gravity makes it go deeper. It is this pull subduction that keeps plate tectonics going.

So, what about Venus? The usual answer is that Venus had a stagnant lid, but at certain intervals the internal heat is so great there is a general overturn and there is a general resurfacing. However, maybe that is not exactly correct. Our problem with Venus is we cannot see the surface thanks to the clouds. The best we can manage is through radar, and recent (June, 2021) information has provided some surprises (Byrne, et al.,   https://doi.org/10.1073/pnas.2025919118).  Basically, what was found was evidence that many of the lowlands had broken into crustal blocks and these blocks are moving relative to each other, in the same way as pack ice moves. The cause would be mantle convection that stresses the crust. The Venusian crust has many landforms, including thin belts where crust has been pushed together to form ridges, or pulled apart to form troughs. However, these ones tend to encompass low-lying regions that are not deformed, but rather appear to be individual blocks that shift, rotate and slide past each other. The authors suggest this what Earth was like before plate tectonics got going.

As to why they started here and not there has no obvious answer. The fact that Earth rotates far more quickly will generate much stronger Coriolis forces. It may be that the absence of water on Venus removes a potential lubricant, but that seems unlikely if blocks of crust are moving. My personal view is that one key point is it needs something to force the crust downwards. Eclogite may pull it down, but something has to push the basalt down to force it to make eclogite. My guess here is that Earth has one thing the other rocky planets do not have: granitic continents. Granite floats on basalt, so if a basaltic mass was pushed against a significant granitic mass, the granite would slide over the top and its weight would push the basalt down. When it made eclogite, the denser basalt would continue its downward motion, pulling a plate with it. Is that right? Who knows, but at least it looks plausible to me.

Where to Look for Alien Life?

One intriguing question is what is the probability of life elsewhere in the Universe? In my ebook, “Planetary Formation and Biogenesis” I argue that if you need the sort of chemistry I outline to form the appropriate precursors, then to get the appropriate planet in the habitable zone your best bet is to have a G-type or heavy K-type star. Our sun is a G-type. While that eliminates most stars such as red dwarfs, there are still plenty of possible candidates and on that criterion alone the universe should be full of life, albeit possibly well spread out, and there may be other issues. Thus, of the close stars to Earth, Alpha Centauri has two of the right stars, but being a double star, we don’t know whether it might have spat out its planets when it was getting rid of giants, as the two stars come as close as Saturn is to our sun. Epsilon Eridani and Tau Ceti are K-type, but it is not known whether the first has rocky planets, and further it is only about 900 million years old so any life would be extremely primitive. Tau Ceti has claims to about 8 planets, but only four have been confirmed, and for two of these, one gets about 1.7 times Earth’s light (Venus get about 1.9 times as much) while the other gets about 29%. They are also “super Earths”. Interestingly, if you apply the relationship I had in my ebook, the planet that gets the most light, is the more likely to be similar geologically to Earth (apart from its size) and is far more likely than Venus to have accreted plenty of water, so just maybe it is possible.

So where do we look for suitable planets? Very specifically how probable are rocky planets? One approach to address this came from Nibauer et al. (Astrophysical Journal, 906: 116, 2021). What they did was to look at the element concentration of stars and picked on 5 elements for which he had data. He then focused on the so-called refractory elements, i.e., those that make rocks, and by means of statistics he separated the stars into two groups: the “regular” stars, which have the proportion of refractory elements expected from the nebular clouds, or a “depleted” category, where the concentrations are less than expected. Our sun is in the “depleted” category, and oddly enough, only between 10 – 30% are “regular”. The concept here is the stars are depleted because these elements have been taken away to make rocky planets. Of course, there may be questions about the actual analysis of the data and the model, but if the data holds up, this might be indicative that rocky planets can form, at least around single stars. 

One of the puzzles of planetary formation is exemplified by Tau Ceti. The planet is actually rather short of the heavy elements that make up planets, yet it has so many planets that are so much bigger than Earth. How can this be? My answer in my ebook is that there are three stages of the accretion disk: the first when the star is busily accreting and there are huge inflows of matter; the second a transition when supply of matter declines, and a third period when stellar accretion slows by about four orders of magnitude. At the end of this third period, the star creates huge solar winds that clear out the accretion disk of gas and dust. However, in this third stage, planets continue accreting. This third stage can last from less than 1 million years to up to maybe forty. So, planets starting the same way will end up in a variety of sizes depending on how long the star takes to remove accretable material. The evidence is that our sun spat out its accretion disk very early, so we have smaller than average planets.

So, would the regular stars not have planets? No. If they formed giants, there would be no real selective depletion of specific elements, and a general depletion would register as the star not having as many in the first place. The amount of elements heavier than helium is called metallicity by astronomers, and this can vary by a factor of at least 40, and probably more. There may even be some first-generation stars out there with no heavy elements. It would be possible for a star to have giant planets but show no significant depletion of refractory elements. So while Nibauer’s analysis is interesting, and even encouraging, it does not really eliminate more than a minority of the stars. If you are on a voyage of discovery, it remains something of a guess which stars are of particular interest.