How Long Since?
Everything is always weathering.
The process follows the laws of chemistry and physics.
The track and the undisturbed soil around it both change, with differences.
Weathering is constant, the rate is not.
Concept Illustrated: Weathering – Wind-blown sand
The idea: “How long ago did this happen?”… Fortunately, soil dries and wind blows.
Different shades … the edges and bottom of a stone nudged out of its bed, the earth it exposed, or displaced. These and other signs in and around a stone sometimes provide a fairly accurate estimate of when a track was made, disturbed, or when a foot nudged the stone, and in a general way how much energy the animal was exerting.
Though precision of estimates based on this method will diminish Over time, accuracy of the estimates can sometimes be down to minutes, or even less. In some soils differences in shades of color can remain distinguishable for quite some time.
Concept Illustrated: Weathering – 24 hours in the life of a track
The idea: A track changes constantly, even if left un-disturbed. Even if one observed that track for 24 hours straight, the gradual rate of some weathering and aging processes might make them almost invisible to the mind.
And isn’t learning to notice these kinds of changes one of the must-succeed-at challenges in becoming able to age tracks? Would it shave time and error off the learning process of track aging if one could help the mind learn to observe these kinds of changes by compressing them into an easily viewable time frame?
Concept Illustrated: Weathering – Changes in shade of color caused by loss (or increase) of soil moisture.
The idea: Illustrate two different substrates changing color over several hours. Begin from the moment a track is made and continue as soil moisture evaporates.
As a track is created, surface material may be pushed down or compressed into close contact with the sub-surface material, some of the existing sub-surface material may be exposed, or even lifted away. Results of these events may include changes to the appearance of the involved surface material: moisture lost to a dryer substrate, or absorbed from wetter soil. At temperatures above freezing, when newly disturbed soil dries, its color generally lightens as the level of moisture content decreases, until it reaches a shade similar to the surrounding undisturbed soil, or sometimes even a lighter shade when thin sections dry more than the undisturbed soil.
Concept Illustrated: Weathering – Rain … How does It affect a track? Which results of this process become useful tools for reading a track’s age?
The Idea: Ever go out and sit through a rain, watching how it affects a track? Even if you have, were there changes to the track you were unable to notice? Would an illustration summarizing the significant changes help to learn how to use the rain-related changes as tools for aging tracks?
The process doesn’t really start here, but it’s a good beginning. The first raindrop lands, a bunch more follow, to land on the ground’s surface in and around a track, and the rain continues. If it soaks in, the water seeps downward into the substrate and, if the soil isn’t too porous, begins to accumulate. As the soil gets wetter the physical effects of falling raindrops begin to alter the track, and flowing water may contribute as things begin changing. Among those changes; physical properties are altered, the soil color may change, soil may be moved into or out of the track, ridges may slump, even the entire track can be erased.
Immersing yourself further in nature is an irreplaceable learning tool, and unavoidable (you already are) with hidden benefits, and some dangers … when you do go out in the rain, be aware of and take precautions against one-on-one lightning encounters, thumping big hail, and dumpster winds.
How much useful weathering information does a rain process create? Does anything fill in a track, or wash stuff out of it? What determined how fast that happened? Once the rainfall had traveled on, how long does it take water pooled in the track, to clear, sink in, or evaporate … or the soil where the water had pooled to dry?
The goal here is to make a start at visually summarizing these processes in a way that facilitates a tracker learning tyhis tool for use as part of reading a track’s age. Do the questions above include all the useful information? And how long does this age information last? Just till the rain stops? Till … the puddles clear or evaporate … or the soil dries completely … or the next rain? What if all those questions were visually summarized for each of the various common soil types?
Concept Illustrated: Weathering – Edges… All tracks have ‘em, and each is eloquent. Any edge holds a bit of the story; time that’s passed, forces employed, and that’s not all. And by the way, the compressed surfaces are also yield information.
The idea: Edges change as they weather. Is it a smooth steady process? Intermittent? Speeding up with the wind? Slowing at night? Do dry sand and clay weather at the same rate, or in the same ways?
Some of these changes are predictable and obvious; the initial changes in a track left in very dry sand for example. What about the subtleties? Will emphasizing some of these help beginning trackers improve their skills a little faster?
It’s one kind of learning experience is to observe changes in a track by returning every hour or two; but what is it like to watch them as they change? Can that really be done without expensive equipment and some specialized knowledge of photography?
What follows is descriptive information about reading the age of tracks, included because each topic is a potential learning obstacle to beginning trackers, and so possibly worthy of clarification. It is not meant as instruction. If you find a mistake, disagree with any of this information, or think there even might be an error, please contact the author … to have value this work must be accurate.
Figuring out when a track was left (aging it) is a fundamental and useful tracking concept
Accurately locating a track or trail in time provides useful information that can move the tracker an important step closer to understanding interactions within the natural community. People lost outdoors have been rescued alive because a team of skilled trackers identified and followed the most recent part of that person’s trail.
“Weathering“: the changes in a track’s appearance, shape, and physical properties due to weather, and other natural processes.
The causes: include external environmental events like wind and rain, as well as persistent natural forces like gravity, time, and even evaporation. Some have cyclical patterns like sunlight, and there are less subtle singular events like tsunami and meteor strikes.
The physical properties of the particular substrate a track is created in have some influence on how it responds to the causes of weathering. Take sand and clay as an example; wet sand holds details well, but it tends to dry out, then, well, sand slumps and details fade. Damp clay holds tracks very well, and the tracks and details it does preserve tend to last.
The effects: can include change in color, contents, shape, and even composition (dinosaur tracks left in mud or clay have metamorphosed into stone). Even the location of the track can change because some geological processes can move very large things like wetlands and lake beds.
See, the thing about track weathering is that both the soil disturbed when the track was created, and the undisturbed soil are weathering at the same time but the changes are more obvious as the freshly disturbed soil ages. Everything is always
Variability in rates of weathering due to environmental factors … an example; the rate of evaporation
It is important to keep in mind that some causes of weathering, like gravity, occur at a steady rate, and some responses to weathering, like soil moisture loss may occur at a variable rate.
Here’s just one example of work done to describe the process of moisture loss in sand: Weikang Song, Yu-Jun Cui, Anh Minh Tang, Wenqi Ding, Thanh Danh Tran. Experimental study on water evaporation from sand using environmental chamber. Canadian Geotechnical Journal, NRC Research Press, 2013, 51 (2), pp.115-128. <10.1139/cgj-2013-0155>.
Damp sand is held together by surface tension (of the moisture coating the sand), so moisture loss can change a track’s shape. The crisp edges of a track in damp sand will gradually erode and round as the sand drys. The rate at which that happens is influenced by how fast the soil moisture content changes.
When wind is present, the air moving across the sand is carrying away moisture at a faster rate compared to still air, so the number of sand grains held together by surface tension is also changing at a faster rate. So in moving air this particular track will dim faster.
The particular substrate a track is created in has it own physical properties that affect how it responds to the causes of weathering. Take sand and clay as an example; wet sand holds details well, but it tends to dry out, then the sand slumps and details fade. Damp clay holds tracks very well, it dries much more slowly than sand, but may crack and curl as it dries, often the tracks and details it does preserve tend to last.
The observable effects of weathering
There are several, and may not all be noticeable at any given time. They can include change in color, contents, moisture content, shape, and even composition (dinosaur tracks left in mud or clay have metamorphosed into stone).
Even the location of the track can change … some long-term geological processes can move very large areas, along with their wetlands and lake beds.
“Aging“: the process of change in, or to a track over time; the activity of estimating the age of a track.
Estimating age involves examining the signs of weathering in and around the track and trail, and using that along with any other pertinent information to deduce the age of the track.
Unless altered or removed, the signs of weathering are always present and changing, the other ways to age tracks may not be. Except for sightings, tracking collars, and trail cameras, weathering generally provides the most precise timing information.
How long are tracks useful?
For as long as they exist, which can be millions of years, or longer. The following reference is to a paper published in 2002 by a team pulling meaning from tracks that are about a billion years old.
Rasmussen, B., Bengtson, S., Fletcher, I. R. & McNaughton, N. J. Discoidal impressions and trace-like fossils more than 1200 million years old. Science 296, 1112 – 1115 (2002).
There is current scientific interest in fossilized tracks (think dinosaurs). Scientists are developing the discipline of “Neoichonology” by employing all the relevant tools of modern science to interpret these tracks and glean as much information as possible about the animals, and their behaviors.
We already use these skills … and may not realize it
From life experience most of us already read some signs of weathering. You’ve noticed the damp spots left by the first few raindrops? The puddles after the rain, and the mud exposed as that water evaporates, and maybe how later raindrops, feet, or drying affected that mud?
With the right kind of focus, helped along with learning materials shaped to foster it, how hard would it be to figure out how the mud alters with age? Drying to a particular shade of gray, or beginning to crack? In the roadside photo below, would you guess the mud has been uncovered for very long? And which came first, the muskrat or the second rainfall (or was that just water splashed-in by vehicle tires)? Does the right-most track hold any answers? Were all raindrops the same size?
How does a tracker read the age of a track?
It is a deductive process in which one assesses time-related changes to, and in the area of a track to reach an estimate of when that track was made.
The signs of weathering are only part of this process, but one of the most useful because they are always happening, always present, and one can estimate how long those changes took to reach their present state. Other factors are considered as well; these include, but aren’t limited to anything else that can affect the animal’s behavior such as the timing of local weather events, the animal’s usual behaviors, stage of the moon, season …
Even changes in soil compression within the track come into play: “When stress is removed from a consolidated soil (reduced in volume), the soil will rebound, regaining some of the volume it had lost in the consolidation process.” (source:https://en.m.wikipedia.org/wiki/Consolidation_(soil))
A simple example of aging tracks;
– In the morning you cleared an area of ground and fluffed it up with a rake.
– You cut the lawn that afternoon, and planning to avoid alterations to your shoes, mostly watch the mower. and as usual the lawn mower scattered grass clippings far and wide.
– The next morning you’re out enjoying your mowing job and remember that track patch, so you go check. Most of the grass clippings have dried, and their color changed. A house cat left a trail across your fluffed up earth, and the grass clippings that fell into its tracks look undisturbed. Of the grass clippings in the raccoon tracks, some have been bent, others pressed into the soil and have bits of soil on their upper and lower surfaces. The raccoon tracks appear crisper, the edges more sharply defined, and some of the disturbed soil a shade darker than similar areas in the cat tracks, oh, and someone stepped in one of someone else’s tracks.
– You’ve got a rough time frame, you know when you created the track patch, and you can narrow that down even more because you know when you mowed the lawn, and the current time. Further more, some animals tend to be nocturnal, though not consistently. So you know roughly when the two animals crossed the area.
– Comparing the inner edges of the cat and racoon tracks you notice differences in the color of the soil in the two sets of tracks (the shades of the color), one set seems to be a little lighter in color. And if you leave those tracks in place or go back every so often to line up a new one of your own, what else can you learn?
The signs of weathering one looks for?
Are many and some vary with the seasons, or even time of day. A few are: changes caused by rain, the degree of edge crumbling or rounding, wind-blown debris or objects fallen in, erosion, changes caused by expansion and contraction, change in color, more recent tracks.
Making one’s own list of the causes of weathering, the signs and the ways they change is no waste of time!
Signs can be influenced by multiple factors. What might influence the signs in this situation:
– it’s mid-morning and you’re walking east. You reach a stream and find tracks.
– a barefoot human track left on a shaded rock the sun hasn’t reached, the track still damp but just visible, and headed west …
– after you cross the stream, you find a trail of larger barefoot human tracks. The closest is really wet, headed east, and on a rock that’s been in the sun for a while?
– Could stream flow have carried anything away?
– Would the higher levels of humidity beside the stream slow evaporation of wet tracks?
How does one interpret the signs?
Noticing the signs: is the necessary first step.
Interpreting: them is the next waypoint: learning what signs mean, what causes them, and how they change over time. Questions usually help (they’re also a good source of material for illustrations). “Why is that different?” is frequently fruitful.
An example: it’s late spring, would there be any differences in how the broken end of a living twig weathered if a moose browsed off the rest, or a lost hiker tore it off while blundering through? Maybe a different break, but same rules of weathering, right? But could moose saliva affect the weathering of the exposed parts of twig, changing how long break looked fresh?
Groups of sign
It often helps to combine the info from more than one sign of weathering. An example, it’s six a.m. on a summer morning. The shape of that deer track (it’s soft soil) looks pretty fresh, maybe less than an hour old, as do the colors of the soil in the track. But there’s a bird track, maybe robin-sized, crumbling one edge of the deer’s track. When do robins usually start foraging?
Variations in the same kind of sign
The variations specific to things that cause weathering are helpful. Take wind as an example; in what ways might wind affect the weathering of a track? What kinds of differences does wind exhibit in the area where you are tracking? If you consider the possible ways each contributor to weathering can change, the list grows more complex but may be more helpful. Did the wind blow from the south all day, were there strong downdrafts just before that thunderstorm almost happened?
Because the processes of weathering obey the same laws of physics as everything else, there is predictability for all tracks. How, why, and the rate at which they weather is not random. And the news gets better … with a little organization, that list of causes and signs mentioned before can be a real help.
Prediction, a learning tool…
Once the more obvious signs of track aging are understood, it is also possible to predict how a track might appear after some certain length of time. If a track is examined for how it compares to that prediction, it will sometimes reveal another layer of the story. “That track looks different from what I expected, now why…?”.
For example; you know you’re going out to check that track patch you made in the back yard. If there was a track in it, maybe there could be some high points and some lowest spots in the track (and not just the claw holes). Maybe you predict that those different vertical levels wouldn’t weather exactly the same? So if that were true, might there be some observable difference between them?
So you get out there and yeah, there’s an observable difference in some of the tracks. But, since Murphy’s laws only work when you don’t want them to, of course the tracks don’t all match your prediction. And this is when the learning happens, you ask yourself, “Why are some different from what I predicted?”
Think a track’s location can’t change? There are lake beds that still preserve tracks of dinosaurs. Over the millions of years, how would a lake bed change in location, elevation, or tilt, as the various geological processes change the surrounding land into mountains?
Precision of age estimates (how close you can resolve the timing) … Expectations and reality
Precision of an age estimate can vary, even within a trail, from “Exactly at” to “Probably was”. And there can be a lot of “Between some time and now”. Though not always, there is usually some degree of uncertainty in an age estimate.
When exact age is not possible, it must be estimated. Estimates can depend on one’s knowledge, experience, and state of mind (tired minds don’t work as well), plus all kinds of other factors. An example would be physiology; do you perceive shades of color exactly the same as other people?
The difference between your expectations and reality can be fuel to motivate you to ever greater precision. Read every track to the minute, hour, and day of its creation? Sure, that’s a great expectation for a beginning tracker, probably unreachable, but if that was modified to a realistically ambitious goal would it help one improve?
When reality tempers those expectations, beginning trackers can and probably will get discouraged. So? Does one quit or keep nudging? This area offers much … material for the illustrator, hope and improvement for the student tracker.
Accumulating experience can nurture ability, and improve precision.
The more you look the more you see, and the brain accumulates experience as one goes about their daily patterns, which means there is learning value in just noticing tracks every day.
Grandfather Pa Jay was a Texas farmer with a huge garden, chickens, pigs, and large pastures for his cows. While caring for his farm he put in dirt time every day. He tended to notice his animal’s tracks, and by observing them every day, he was subconsciously accumulating experience at reading the age of tracks. Eventually he was able to age tracks to the year, month and day, years later and even clear across one of his pastures … he got real good at it after they built that railroad through his north pasture.
Not all trackers are as lucky as Pa Jay. Tracking can be an irregular kind of experience … Only on weekends maybe, or sometimes precision of aging is nearly absolute (you watched the person move down the trail), and other times you’re estimate requires a set of pretty wide upper and lower limits (the age boundaries of fossilized tracks).
Ways to increase the accuracy of one’s age estimates:
Glances– you’re in a hurry, cutting across the park on your bike. On your way back you take the same route. It builds your tracking experience if you just glance at the tracks you made on the way there, or just watch someone walk. No, it’s not detailed analysis, but your mind absorbs more than you think, and each observation adds a bit about tracks with a known age or activity to your tracking experience.
Practice – track boxes give you a controlled environment. Regular checks of the state of tracks you made there give you a sense of how the weathering is going, what the signs are.
Photographs – well, not so much. For some obvious signs like hail, yes. For more subtle differences like changes in the shade of disturbed earth, it takes some knowledge of photography and lighting to capture each photograph with the same shading, lighting, and color tones. How many shades of surface color exist between wet sand and the same sand dried to the bone? Even then, when trying to observe really fine distinctions of this sort out in the real world, natural lighting is pretty flexible, varying more than most of us realize ‘cause our brains are so visually adaptive.
Drawings – yes and no, yes if you’re illustrating some weathering-related feature.
Network – with other trackers about this topic.
Observe with focus – how many tracks have you seen made, and really paid attention?
Look for patterns – Fred and Wilma are walking slowly down a flat road covered by 1/4 inch of new snow. Wilma is explaining some complicated thing to Fred, who likes to be sure he understands so he asks lots of questions. Fred likes to look you in the eye, so he slows and turns a little towards Wilma every time he asks a question, then resumes his regular pace. Each time, Wilma slows a bit, but keeps walking right ahead, explaining her way down the road.
Write descriptions – pick some sign of weathering then describe it and its changes as accurately as you can. Read your description aloud, correct it, and put that away for a few days. Next time you think of it read it again … repeat until you can’t find any more changes to make. Now have another tracker read it to see if it makes sense to them, or if you missed something. You will learn from this one!
Trails can have age indicators – so use them also. You may find one clear and certain age indicator for the trail that puts everything else in its proper time-perspective. And keep in mind that when you’re following a trail, one direction is going only further back in time, sometimes a lot.
Walking the same route – There are benefits and drawbacks. We all tend towards patterns in our travels, so regularly walking a road can help you to see these. For learning to read the age of tracks this can help. Today you walk the same route as yesterday and find moose tracks that weren’t there yesterday, now you know something, maybe a bit of that moose’s pattern, and for sure a fragment of that road’s use history. Or, you can still see some of the tracks where, last fall, after coming down the ancient trail and crossing the road, a herd of elk descended that 45 degree slope towards the stream?