Ordovician Sea Color?

[Bev]

Hmmmm, do the scientists think that the Ordovician Seas were blueish or greenish? Or was the Earth of enough of a different chemical composition that the seas may have been another color? I've heard speculation that Earth's skies were not always blue...

[Bev]

As long as I am asking questions, would there have been floating plants on top? If so, any idea of what they would have looked like?

I'm setting up a new 5' long dry aquarium for my fossil collection and I want to make it look like an Ordovician Sea bottom. It has a residue along the top of the glass that I can't seem to get off with glass cleaner, vinegar, snobol, or limeaway - a razor won't even scrap it off. So I'm thinking some aquarium plants siliconed on the top inside will hide it.

[howard_l]

My understanding is until enough Oxygen was introduced into the Oceans to oxidize the iron and form the iron deposits as found in Michigan the color could have been red then green then blue. Most of this occurred in the Cambrian but the Ordovician may not have been as blue as today.

[Bev]

Thanks Howard! Most of the pictures show a blue, but somewhere I thought I had red in iron rich areas which SE MN is fairly rich in iron ore. Green makes sense just from plankton, but then plankton can be red...

Graptolites were the floaters.

[painshill]

Hi Bev

These are good and - I think - interesting questions. The colours we perceive are the result of particular wavelengths of visible light being preferentially reflected or scattered, rather than absorbed by whatever they fall on or pass through.

I’ll comment on sky colour question first since the colour of the sea is – at least in part – influenced by the colour of the sky (from reflection).

The colour of our sky is the result of “Rayleigh scattering” whereby the gas molecules in the atmosphere scatter the shorter wavelengths of blue and violet light from the Sun rather more than the longer wavelengths in the orange/red area of the spectrum. Although water vapour in the air plays a part, the major effect is from the gaseous components (primarily nitrogen and oxygen today). As the sun sets, its light has to pass through a larger expanse of the atmosphere such that the blue and violet part of the spectrum is so completely scattered that we no longer perceive it at all and only the red and orange parts of the spectrum are visible.

During the day, the sky is technically violet rather than blue (because that’s the shortest wavelength in the visible spectrum and the most prone to scattering). The receptor cells in our eyes which allow us to perceive colours (known as cones) come in three types but with sensitivities to overlapping wavelength ranges. The combination of blue and violet scattered light is only perceived as if it were blue (and white) light, so we don’t perceive the violet colour.

The sky probably hasn’t always been blue. Assuming our belief that Earth’s early atmosphere was methane-rich is correct, the physics suggest that it would probably have had an orange cast during the day, becoming even more vivid at sunset. The sky probably got bluer as the oxygen levels rose between 2 ½ and 2 billion years ago and probably reached what we would call blue between 1 billion and 540 million years ago. So, yes it would have been blue during the Ordovician but perhaps not as blue as today.

As for the sea... water is a very good absorber of all wavelegths up to the blue/violet end of the spectrum and the absorption effect plays a bigger role than is the case for sky colour. The blue/violet colours are again reflected or scattered and so blue is usually what we see from above. Tiny particles in the ocean also enhance that by increasing the reflection and scattering and there is further enhancement in that large bodies of water tend to reflect the predominant colour of the sky. Viewed from below, the remaining transmitted light is stripped of pretty much all the wavelengths apart from blue/violet and so the sea appears blue at least down to about 200 meters. Beyond that, it just gets darker until you get to about 2,000 meters where virtually no light penetrates.

Green colours are usually the result of algae and other microscopic life with chlorophyll pigmentation (and algal bloom can also create unusual colours such as the “red tide” phenomenon). The observed colour is also modified by suspended sediments into dull grey and brown colours. Storms, river deltas, underwater subsidence or volcanism would all play their part (both now and in the past).

I would think that all of the colours of ocean that we observe today would also have been present during the Ordovician for the same kinds of reasons and what colour you saw would depend on exactly where you were and what the topography, climate and nutrient composition of the water were in that area.

Earth’s early ocean was rich in iron, which would have influenced its colour, but the iron was deposited on the ocean bed in huge quantities as oxide-rich ores between 3.5 to 2.5 billion years ago. Thereafter, iron content in the ocean played a less significant role in determining its colour and probably had little relevance by Ordovician times.

What we know about Ordovician oceans is that they were what are called “calcite seas” with a geochemistry dominated by low-magnesium calcite (from animals and macroalgae with calcareous skeletons) and that they were effectively calcium saturated. At the beginning of the Ordovician, there was a strong greenhouse effect from carbon dioxide in the atmosphere and ocean temperatures were generally believed to reach around 45 degrees Celcius. Those are good conditions for algal blooms. The climate gradually cooled until, at the end of the Ordovician, we have massive glaciation, draining of shallow seas and a general fall in sea level leading to the Ordovician-Silurian extinction. The decaying remains of the fauna that died would likely have created a highly nutritient-rich ocean for algal bloom to thrive.

Much of the Ordovician environment comprised shallow clear water over extensive continental shelves and fragile reef environments dominated by algae, sponges, some bryozoans and – later – corals. Many areas would likely have had crystal clear aquamarine water but there is also evidence for periods of complete reef collapse arising from global disturbances which would have had a significant but temporary effect on the ocean colour.

Concerning floating plants… graptolites (which in Ordovician times included surface drifters) were colonial animals not plants. There is fragmentary and spore evidence for primitive moss-like plants of a kind formerly known as psilophytes that perhaps lived in shallow water with their sporangia protruding above it. These plants probably also began colonising terrestrial environments in the Ordovician, but there were no vascular plants as far as we know. Those didn’t appear until the Silurian. The evidence suggest that plant life in the Ordovician was dominated by microscopic green and red algae floating on or just below the surface of the water.

Edited June 2, 2014 by painshill

[Auspex]

A thorough and well-crafted reply!

Now, the next question for recreational musing: how did trilobites perceive color?

[painshill]

A thorough and well-crafted reply!

Now, the next question for recreational musing: how did trilobites perceive color?

Aaaah… but did they?

There are multiple instances of trilobite fossils with what appears to be original colouration, including some with what may be camouflage spotting. But even if trilobites were brightly coloured that doesn’t necessarily imply that they could see that colouration themselves and – in the case of camouflage spotting – it may have been the pattern rather than the colouration that was significant.

Of the three trilobite eye types, the schizochroal eye perhaps shows the most promise for an optical mechanism that allowed colour recognition (Stockton & Cowen 1976). Searching for something modern with which to make a comparison suggests that the eyes of extant Strepsipterans have many structural similarities, as do the eyes of some sawflies such as Perga (Horvath, Clarkson & Waltraud 1997).

Behavioural observation of Perga also suggests that its larval forms are capable of polarization sensitivity, motion detection, form and colour perception despite only having simple eyes (Weiss et al. 1944; Wellington et al. 1957; Came 1962; Meyer-Rochow 1974). Those simple eyes – known as stemmata or lateral ocelli are present in Strepsiptera as clusters and feed into photoreceptors known as retinulae. In a sense, they’re simplified compound eyes. We don’t know if trilobites had anything similar, but there are certainly structural similarities.

[Bev]

Thank you so much Painshill!

So, depending upon where you were when, the sea could have been red (algea bloom), green or blue, or any variation thereof. But most likely when calm in the green/blue range.

[piranha]

On 6/2/2014 at 9:21 AM, painshill said:

Of the three trilobite eye types...

 

 

More recently it is has been suggested that holochroal and schizochroal are the only two trilobite eye-types:

 

Quote

The eyes of eodiscoids were described as abathochroal by JELL (1975b), who considered them to be distinct from holochroal eyes since the lenses were somewhat separated from one another, along with a summary that the eyes of eodiscoids resemble holochroal eyes in five respects, and there are eight differences from the schizochroal type. Of these, two key features for establishing these eyes as a separate type are the lenses not being in contact with any of the surrounding lenses, and each lens possessing its own corneal membrane. However, with more and more phospatized material being documented, and especially with the more fully detailed morphological examination of the visual surface of the eodiscid Pagetides, our new observations do not support the view that abathochroal eyes are distinct from the other two well-known types.

 

For instance, JELL (1975b) believed that each of the individual lenses carried its own corneal cap, but the fact that the outermost thin layer of the visual surface can flake off, taking with it many lenses together, rather than just a single one, casts doubt on this interpretation. Actually, the internal surfaces of some librigenae with the visual surface attached show that some of the fine lenses are polygonal in outline (Plate 16, Fig. 7), rather than circular as seen from the external surface. This is because these lenses remained in close contact as they grew towards a centre point of the visual system, and this has led to the deformation of the outline of lenses from circular to mostly hexagonal, as well as a few pentagonal and quadrilateral (also see ZHANG & CLARKSON 1990, pl. 2, figs 2-6). Moreover, it is now known that the juveniles of holochroal-eyed trilobites have separated lenses ( CLARKSON & ZHANG 1991, CLARKSON & TAYLOR 1995), and that they are likewise separated in the paedomorphic Ctenopyge ceciliae (CLARKSON & AHLBERG 2002).

 

If eodiscoids are indeed paedomorphic derivatives of holochroal-eyed polymerid trilobites, is it not likely that they would have separated lenses too? It may be, therefore that the concept of abathochroal eyes as a separate eye type, though adopted earlier CLARKSON (1997) is no longer sustainable, for the moment we leave the question open. In the descriptive part of the text, accordingly, we describe the eyes of eodiscids as abathochroal, because this term to date remains absolute as only known from eodiscoid trilobites.

 

Zhang, Xi-Guang & Clarkson, Euan N.K. (2012)

Phosphatized eodiscoid trilobites from the Cambrian of China.

Palaeontographica Abteilung A., 297(1-4):1-121

 

 

 

[Auspex]

I would not expect a marine organism (even a shallows dweller) to have any use for visual sensitivity in the UV spectrum, so using the terrestrial arthropod eye as a model might not be the best approach.

Any idea as to what the world looks like to a horseshoe crab?

[painshill]

I would not expect a marine organism (even a shallows dweller) to have any use for visual sensitivity in the UV spectrum, so using the terrestrial arthropod eye as a model might not be the best approach.

Any idea as to what the world looks like to a horseshoe crab?

It’s pretty darned difficult checking these things, so most researchers in the past have used the relatively unsophisticated technique of checking for statistical bias in congregations of animals against backgrounds of different colours or whether they are drawn to light sources of particular wavelengths.

It’s a bit like the old gardening trick – try laying out a sheet of bright yellow polythene coated in insecticide if you want to keep the greenfly off the produce in your greenhouse.

Horseshoe crabs ain’t the most co-operative of subjects but Srijaya et al. attempted to determine colour preference and light sensitivity in larvae (25 day hatchlings) of the mangrove horseshoe crab, Carcinoscopius rotundicauda. The results (albeit using small sample sizes) were pretty marginal.

The larvae showed a preference for ultra-violet lights, whether shone horizontally or vertically. They also showed a directional preference in the visible spectrum for the colours yellow, blue, orange and white but it was only statistically significant for the lighter colours: white, yellow and orange. There was also a directional aversion to green, red and black which was only statistically significant for the darker colours: black and red.

I have no idea why some terrestrial arthropods have eye structures which have so much similarity to some trilobites. Their selection as a “model” was perhaps more about understanding the possible mechanisms by which such simple eye structures were able to respond to colours in the visible spectrum than it was about (the absent) taxonomic relationship or any belief in similarity of lifestyle/habitat.

Edited June 2, 2014 by painshill

[ashcraft]

I suspect they are similar because they evolved from the same stock cells. Eyesite has evolved and re-evolved many times, but the eyes function in a very similar fashion. As I recall from herp class, snakes were a fossorial group that had lost their eye site, then they re-evolved it when they re-emerged above ground. Even so, we still recognize them as eyes.

As I recall, both insects and reptiles can see UV light. Humans can see it somewhat (as a glow). Reptiles can "see" infrared, we can sense it as heat before we touch the hot object. How big a jump is it from "feeling" heat to "seeing" heat?

My labored point is that the tissue that develops into eyes is ancestral to most animals with eyes and tends to evolve in a similar fashion because it has to.

At least that is my opinion. That and $1.50 will get you a soda in our lounge.

fkaa

[Auspex]

.....tends to evolve in a similar fashion because it has to...

.....tends to evolve in a similar fashion because when it yields a competitive advantage has to and can physically do so...

The soda's on me

[RyanNREMTP]

I have to say that this has been a very interesting read. Too bad I don't have anything to contribute to it.

[ashcraft]

.....tends to evolve in a similar fashion because when it yields a competitive advantage has to and can physically do so...

The soda's on me

I am not so sure about competitive advantage, at least initially. In my opinion, mutations that are not deleterious occur in a species and through random chance build up in a population causing a variation of response to stimuli. If these responses at some point become either helpful or harmful, their percentage of the gene pool changes.

Most mutations are recessive, and aren't even expressed as a phenotype when they first occur. Even a dominate allele at first mutation is such a small percentage of the gene pool that it is unlikely to remain, even if selected for. However, mutations occur frequently enough, that by chance, some will make it (genetic drift) expanding the gene pool, allowing for variation in response, which ultimately may allow it to be selected for by allowing some organisms to survive more frequently.

fkaa

[Auspex]

We may be saying the same thing from slightly different perspectives.

I think in terms of "genetic propensity" at the microevolutionary level, which assumes that the chemistry must be present (whether old gene, recessive gene, or new mutation) before its effects can be manifest. This keeps me out of the molecular biology arena, and avoids any hint of 'purposeful goal-driven' evolution.

[Mr_ed]

Wow! very interesting....

Painshill.. can you tell us if fish such as Rainbow Trout can see color or what colors they can see.. I know this doesn't have anything to do with fossils, but it is of great interest to me.

Thanks

Ed

[Auspex]

Wow! very interesting....

Painshill.. can you tell us if fish such as Rainbow Trout can see color or what colors they can see.. I know this doesn't have anything to do with fossils, but it is of great interest to me.

Thanks

Ed

I can state from personal experience that Brook Trout distinguish colors.

[painshill]

The eyes of most fish have many similarities to terrestrial vertebrate animals – they have a retina with both rods and cones and the latter are the usual mechanism that allows colour perception. In most fish the cones are double structures and each part of the doublet may have a different peak wavelength absorbance that potentially allows greater discrimination between colours than our eyes can achieve. Most fish also have vision in the ultra-violet region of the spectrum which we do not and also the ability to distinguish the degree to which the light is polarised – which again is not something our eyes can perform. The vision capabilities of particular fish also generally exhibit modifications or adaptations which are specific to their individual habitats or lifestyles.

Human eyes have three types of cones that are broadly receptive to red, green and blue (but with some overlap that means we have difficulty distinguishing some shades of colour – especially in the blue/violet region). Rainbow trout have four types of cones which are responsive to: red (including longer wavelengths than we can discriminate); green (similar to humans but with better discrimination in the yellow/green region); blue (also similar to humans but with better discrimination in the blue/violet region); and ultra-violet (which we don’t have). That fourth type of cone disappears in trout that are more than two years old but it is believed that it may reappear annually in mature trout as a navigation aid for spawning runs by assisting in detection of polarised light.

So, in general, trout can see brighter reds than we can and at lower light levels and their ability to discriminate small differences in hue is mostly better than we can achieve. While that’s the capability they have, it’s only realised when the full spectrum of light is present and it’s also limited by the quality and intensity of light. They probably can’t see much colour at all beyond about three to four meters and as dusk approaches the cones gradually recede into the retina, allowing the rods to take over, such that the ability for colour discrimination pretty much disappears at night. Consequently, colour vision in trout is generally limited to relatively clear shallow water with decent light conditions over short distances; trout probably can’t see much of anything at all beyond about ten meters. They’re then relying on their other senses. Like the majority of fish, trout are near-sighted.

I have no interest in fishing beyond the consumption of the catch, but if your question relates to whether the colour of bait/lures/flies and such for fishing purposes can be used to advantage, it’s worth bearing in mind that the scattering and absorption of light in water (collectively known as attenuation) means that the colour of a lure will almost inevitably be seen differently below the water than when out of the water. Attenuation works in two ways – the light coming from above (directly from the sun) is attenuated in proportion to the depth it penetrates; and the light reflected from a lure is further attenuated in proportion to the distance it travels to the eyes of fish. Both of those effects are further influenced by the clarity of the water with respect to suspended sediments or staining.

For light coming from above, at depths around three meters the red wavelengths are depleted; at around ten meters the orange and yellow are depleted too. The same thing happens for light travelling horizontally which has been reflected towards the fish from a lure – it will be further stripped of those wavelengths depending on how far away the lure might be. The consequent effect is that the apparent colour of the lure progressively moves through greenish and bluish greys to blue/violet and ultimately black. So, the colours a fish will actually perceive (as opposed to what its eyes are capable of seeing) depends on a combination of how far through the water the light has travelled to reach the lure and how far it has to travel through the water from the lure to the fish.

The colour of a lure would need to be matched to specific feeding preference colours based on the similarities of colour under the water to have any advantage. Since fish are often looking upwards when feeding, they may only see a dark silhouette with no apparent colour, so contrast against the light from the sky may be rather more important than absolute colour and black or deep red would actually be the most visible.

Contrast on the lure itself by using two colours may also help. Rainbow trout are not primarily piscivorous although they will of course eat smaller fish and almost all fish that serve as food for larger species have a darker dorsal colour on top of a lighter belly colour. Choosing a pair of colours with exaggerated contrast will make a lure more visible as well as increasing its resemblance to small-fry. Whether it’s also more attractive may depend on the colours but also on pattern resemblances, general shape and movement behaviour (such as popping or spinning in the water or from casting techniques). Red plus white is generally a good combination and so is “chartreuse” (mid-way between green and yellow) plus white.

It’s worth mentioning fluorescent colours of the kind not normally found in nature since they respond to ultra-violet light in a way that potentially makes them more visible to fish and over longer distances. That response can make a lure much more vibrant in colour, which is especially noticeable on cloudy and grey days (but much less so on sunny days). Generally, the fluorescent colour needs to have a slightly longer wavelength than the colour of the water - so red, orange, and yellow are better than green or blue but again chartreuse works well. The dirtier the water and the greater the depth, the less difference it makes, although UV light penetrates to greater depths in water than visible light so fluorescent colours can be still be seen at greater depths.

Edited June 6, 2014 by painshill

[Bev]

Wow, Painshill, you are like really super smart!

[painshill]

Wow, Painshill, you are like really super smart!

Naaah... you only know what ya know... and everyone you ever meet will know something you don't.

[Herb]

Seems to me that critters that mostly crawl around would not need very acute eyesight, but rather the ability to detect motion around them in order to avoid being eaten. Active hunters tend to have the most acute vision.

[ashcraft]

Vision serves many functions. Predators can rely on it, having eyes located forward for overlapping fields of view, so they have depth perception. Prey often have eyes on the sides of their head for a wider field of view to better detect movement. Snakes see heat so they can enter nasty little mammal's holes and eat them. Insects detect color to find flowers, with different insects specializing in different colors.

Vision also functions in navigation. Moths use the lighter color sky to know where the horizon is, up so to speak. This is why they fly into lights. UV vision is also thought to aid in navigation. UV polarizes as it travels through the atmosphere, and animals that can see it are thought to see it as lines in the sky, which gives them a sense of direction.

fkaa

[Herb]

I would go with blue-green, no-one will be able to prove otherwise.

[Triceratops]

Wow! I've learnt alot of interesting stuff in this topic!:-)