Everything has an origin.* Some stories of origins are very simple (eg. the current island of Krakatoa from a volcanic blast recorded in history) while others are much more complex (eg. the Grand Canyon). The study of origins is the study and reconstruction of past events. We have eyewitness accounts of some events from the past but mostly we use circumstantial evidence left behind as a result of historical events to inform us about those events ( see Origins Science and Misconceptions of Historical Science for more about the nature of historical science).
In lieu of specific revelation about an objects origins how do we go about determining an objects history? Usually we can infer something about origins by closely examining their context of that objects specific features. From those observations we can deduce events that must have occurred in the past to give that object the characteristics we see in it today.
A few days ago I was pursuing the latest images downloaded from the Curiosity Rover which has now been roaming about the floor of Gale Crater on Mars for over a year. Since leaving a very interesting rock outcrop (see Curiouser and Curiouser: A Mars Curiosity Update) several months ago, the scenery has been a tad boring (see the last image in this post for an example). However, when the image below appeared on my screen I found myself pondering the rock in the center and I asked myself : where did you come from? How did that rock come to exist in this particular place at this particular time? I wanted to know what the origins of this rock were. So I thought we would ask that martian rock and see if it would tell us its story?
NH: I saw you a few days ago and I was wondering what sort of rock you are and where you came from?
Mars Rock (MR): I’m glad you asked, I have been sitting here for so long with so little to do! In fact, I’ve been here so long I’ve grown a little fuzzy about my exact origins but I’ll tell you what I can. It’s especially difficult to point to my exact birth as a rock because I am not like a lot of other rocks you see around me. For you see, I am a conglomerate.
NH: A conglomerate? What does that mean?
MR: A conglomerate rock is a rock that is composed of many smaller rocks cemented together. If you look at me closely (just go ahead and click on me!) you will be able to see quite clearly that I am made up of hundreds of small stones that are embedded in a sandy matrix.
NH: If you are composed of many smaller rocks where did those rocks come from?
MR: Well, this is why I say I’m a little fuzzy about my exact origins for really I am the sum of many parts each of which have their own origins story. But, I can tell you that I’m pretty sure that I was born as a conglomerate in an ancient stream bed of some sort. I say that because the parts are mostly rounded and they have diverse compositions as you can see from the many different colors and textures of my parts. My parts could only have become rounded by the action of tumbling around against other rocks and that probably would have happened in some running water. Some might say that wind shaped those stones but water is by far the simplest explanation for my stony origins. The different compositions also suggest a stream because my stones must have come from many different sources. To have stones of many sources all together in one place would require an agent to bring them together and a stream, river or some large flood would best explain my mixture of parts.
NH: Ok, your parts come from many sources but how did they become stuck together?
MR: Pretty simple really, I was part of a larger gravel stream bed that was then covered by many more layers of sand and rocks. As some point water seeped through the sediments and minerals and salts in that water precipitated in the sand that filled the pores between the buried stones and caused a from of cement that glued all my parts together.
NH: That makes sense but if you were buried under layers of sediments how did you get where you are today as a lonely rock on top of the soil with no one else next to you?
MR: My life was not very exciting as I sat there slowing getting stronger and stronger as my parts got more and more cemented together but after what must have been 100s of thousands of years a very dramatic thing happened. Suddenly I heard a great bang and I found myself suddenly breaking away from the friends I had been connected to for so long and I was thrown up into the air. The light, after so much darkness, blinded me but I could feel myself flying through the air and then falling to the ground and rolling for some distance. When I came to my senses I found myself sitting among out on this huge plain of dust, sand, pebbles and a few other rocks that seemed nothing like the the friends whom I had shared my prior existence. I have been sitting right here ever since that amazing day. Some of my new friends that were here before I was have told me that there was an explosion a few miles away and that right afterward they saw me crash down right here. Apparently some rock from space fell down onto our planet and caused me to be uprooted from my home not that I am complaining.
NH: So I guess you have been sitting here for quite a while. What is your typical day like now that your are out in the open?
Oh yeah, I’ve been sitting here for many 10s of thousands of years and maybe much much longer. When you are as old as I am time just seems to fly by! My daily routine is pretty simple. I get a bit warm (maybe just above the freezing point of water) during the day in the Mars summer and then I get really really cold every night. This causes my parts to slightly expand and contract each day. Because I am a conglomerate some parts of me expand a tiny bit more than others and this causes slight stresses which lead to minute cracks. As you can see the sand and cement that was holding my larger rocks together has been falling away causing some of the larger pebbles and stones of my body to fall off and now they surround me like so many little offspring. Of course there is a slight breeze here to and once and a while a burst of wind may hit me. Its been that way for thousands of years but over time Mars tilts causing some global weather changes so I have experienced colder nights and at time even some carbon dioxide frost has been known to coat me. In those times, I aged a bit faster than I am aging today but even so not even as fast as your rocks from a place like Utah on your planet. With conditions as they are today or even that I have every experience in the past it has taken many 10s of thousands of years for me to have shrunk to this point from my youthful days after I was tossed onto the surface.
NH: What do you think will happen to you in the future?
MR: Well, assuming you don’t poke me or shoot me with your little laser toy on your way by, I expect that I will continue to hang on for at least 10,000 more years but possibly several hundred thousand years or so after which I will probably have completely fallen apart into all those small stones that I was originally made of. Now those parts are much tougher than I was and wind and thermal tension won’t be able to tear them down so quickly so someday you will probably find a little pile of stones here spread out a bit as they are pushed slightly by the wind and sand over time. On the other hand, it is possible that another meteorite could hit near her and cover me with a blanket of rocks in which case those new friends would shield me from erosion and I might live for millions of years to come.
NH: What about the future of your friends in the area? Do they have the same past and future?
MR: Actually, I have a close friend no more than 100 feet or so away. That friend is also a conglomerate and in comparing our experiences we think that we were both tossed from our underground home to our current resting places at the same time. You will notice (see a picture of my friend below) that my friend is also a conglomerate and looks to be about my age judging by how much he has decayed. But the other rocks in the area are very different, some are volcanic in origin and others were probably clay soils that became cemented together into much harder rocks. As a result they are eroding much more slowly and they actually arrived in this location long before I arrived and will be here long after I am gone. The diversity of our other friends in the area results from their being tossed here from different sources. They probably were thrown out of the ground where they were born from other places in this large crater we call Gale Crater. Some might have even been tossed here from explosions in foreign lands outside of the crater. That’s really great for your studies because you can just stand here and by looking at my friends you can infer things about the history of this whole region.
You see I have come to realize (I have had a lot of time to think about this!) that I am actually sitting on a large debris field composed of loose rocks. Prior explosions threw possible tens of feet of rocks over this whole area. Over a very long time, probably many many millions of years, those rocks eroded with sand filling the spaces in the rock field to form the bumpy rock and sand surface you see today. Somewhere below me there are probably layers of sandstone type rocks or even conglomerates like myself that were present before this layers was deposited. So, despite my age, I actually represent the newcomer to this land. During my time I have seen several new rocks arrive and join us and I am sure there will be others that will join us in the future.
NH: Whoa, are you telling me that you are just a youngster in a field of old rocks but that these rocks are actually sitting on top of some rock layer that is even older? I’ve got to ask – where did those rocks come from and where you around when they formed?
MR: Those rocks are probably before my time but could have been formed during the time when water was at least periodically running down the sides of the crater walls in rivers and streams. Layers of sediments from those streams would have laid down layers of sediments over this entire area that became cemented together to form the rock layers that you have been seeing on your trip.
NH: Ok, so there were processes that made layers of rock that lie under this region and that included the processes that brought the stones together that became part of you. But lets step back a bit further, you keep talking about this Gale Crater you live in. Where did it come from?
MR: Now you are really talking about some ancient history. As I understand it before there could be layers of rock formed inside our crater home that crater had to have been formed. This crater we call home is probably well over a billion years old. A huge meteorite or comet must have come smashing down from above and created this huge crater. Since that time the walls have worn down bringing sediments down onto the crater floor making accumulating to hundreds and even thousands of feet of layers. It was during that time that the rocks that would become the smooth stones that make up me were first formed. I don’t know how it happened but there is also a large mountain in the center of our crater home and it seems to have formed from many layers or dust or maybe a huge lake that filled this entire basin.
Looking even further back it would not be unreasonable to propose that there was even a time before my crater home formed in which the layers of rock that got smashed by that meteorite must have formed by some process of air or water transport of sediments. But this is so long ago it is very difficult to know anything from that time compared to what I know about my recent past.
NH: Do you have any recollection of a large flood occurring in this area around 4000 years ago. Back home we are sometimes told that the rocks on Earth were formed by processes that happened very recently. It has been suggested that at the the same time there was a global flood on Earth there could have been a similar flood event here on Mars. What is your reaction to that?
MR: I don’t know much about Earth rocks but a flood here on Mars only 4000 years ago doesn’t make any sense to me. I sure don’t remember a lot of water around. I’ve been parched for water for as long as I can remember. I expect that if you took a picture of me 4000 years ago and compared it to that lovely portrait you just took that you would be hard pressed to see any differences. I age very very slowly since there is very little around here to cause me to age.
I guess I would have to ask you, if there was a massive flood here 4000 years ago where did all this water go? You have been probing Mars for more than a decade and only recently have you been able to find evidence of some water ice on my surface. 4000 years is a long time but the rocks should be loaded with water signatures had they that recently been soaked in water. I don’t’ think I’ve seen water in these part for hundreds of millions of year. Many of the layers of rock up on that mountain, which you call Mt. Sharp, in the middle of our crater are very likely make of layers of blown dust that have become rock. Dust becoming rock takes a very very long time without water and all that would have had to have happened since this flood you are talking about. It just doesn’t make much sense given everything you and I know about how chemistry and physics work.
Just look at me, I’m a conglomerate. I’m composed of rocks with their own origins. First those rocks had to come into existence and then they were eroded from location and had to tumble around some to form rounded stones. Then those stone had to be collected in one area before being covered and then slowly turned into me. Later I had to be excavated from my origin point thrown up on the surface of the ground and then allowed to erode to the point that you see me today. Even if some great flood could explain my parts the land around here had to be eroded before I could have appeared on the surface and then I would have to have eroded without the benefit of water which, by any measure, would have taken a very very long time. There is no evidence at all that I have been moved or touched by water since I cam to lie right here. Without water, wind and temperature changes are the only forces that have been able to shape me and for me to have been reduced to this pile of rubble in just 4000 years defies all known laws of physics. Oh, I totally forgot that I am laying right inside a huge crater. Before any of that erosion or formation of my parts could have happened the crater had to first be form. When did that happen. I’m really quite confused now because all of my parts and my surroundings are telling me about a series of many events that have taken place in my history most of which could not have occurred at the same time. This flood thing seems to try to explain all these events but that just doesn’t make any sense in light of what I see.
Maybe I’m delusional and all my friends have been telling me tales with respect to their origins stories but my understanding of my origins makes sense given what you and I know about the laws of chemistry and physics. I believe that our laws are the same as your laws on Earth and so I would think that the effects of wind erosion with sand should be something that you can calculate with some reliability once you have measured my surface characteristics like density and composition.
NH: Well, thanks for sharing your story. I am sure that we will be hearing from many of your neighbors in the years to come as our little rover trods across your backyard. We will be leaving you with our tire tracks which I suppose may last hundreds and maybe thousands of years before they are erased by the dust. I think it is very hard for most people to image just sitting in one place for 10s of thousands or 100s of thousands of years. But I wonder what people will say 100 years from now when we stop by and see you again and you look just as you do now? Maybe they will be more likely to believe your story about having sat her for so long. Or maybe they will just say we were not there 4000 years ago to prove that you had not changed even then.
*For me the exception to this would be God who does not have an origin but has created all things.