Tag Archives: sedimentary

Beautiful Kinetic Artwork Sorts River Stones by Age

Fulfilling the job that scientists and unlucky undergrads have been doing for years, the kinetic machine Jller selects and sorts pebbles found on a 6 1/2 x 13 foot platform into a grid organized by geologic age. Without any assistance, the machine analyzes rocks based on their shape and sizes, understand their correct placement and transports them to the right place on the grid.

As automation is starting to take over several industrial activities, it’s also making a strong case in science.The project is part of ongoing research in the field of industrial automation and historical geology, and was presented last December as a part of the exhibition “Ignorance” at Ex Post in Prague. Of course, this only works for a very specific and local context. All the rocks here were taken from a German river of the machine’s own name, most of them being rounded pebbles eroded by the water and glaciers of the Alps. The geological history of the river valley is well known, and therefore it’s fairly simple to date the rocks by age. Jller’s creators, Benjamin Maus and Prokop Bartonicek write:

“The origin of those stones is well documented. For instance, the ones from the river Jller derive from two origins. Some come from rocks, that are the result of erosions in the Alps and are carried in from smaller rivers. Other stones have been ground and transported by glaciers that either still exist, or existed in the ice ages. As the Alps and flats, that were once covered by glaciers, have shifted, even deeper rock-layers were moved and as a result, stones from many geologic periods make their way into a river.”

The sorting takes place in two stages. Firstly, intermediate, pre-sorted patterns are formed first, to make space for the final, ordered alignment of stones, defined by type and age. Jller analyzes an image of the stone it selects, understanding its color composition, lines, layers, patterns, grain, and surface texture. The machine then places the stones in alignment of age and type.

“When the history of a river is known, the type of stone can be directly related to its geological age. One very common sedimentary rock is the dark grey limestone from the Triassic period (225 million years ago). It was formed from the layers of sediments in the primeval ocean. Granodiorite, on the other hand, is an igneous rock of volcanic origin from the Tertiary Period (30 to 40 million years ago). Between those types there is a variety of metamorphic rocks, created by the transformation of existing rock types through the influence of temperature and pressure over time. Furthermore, a small amount of pebbles are formed by non-rock materials like red brick or slag, that have their origin in the Anthropocene.”

The machine could be extremely useful because this work, while not particularly complicated (if the geological setting is well known) can be very time-consuming. Geologists often spend time classifying and identifying rocks and fossils. Machines like this could save a lot of time and effort, allowing scientists to focus on more subtle and challenging tasks. But for now, the machine is part of an artistic exhibition – which is still a start, I suppose. The full presentation video can be seen below:

All photos via prokop bartonicek.

The types of rock: igneous, metamorphic and sedimentary

The three types of rocks

It’s the first thing you learn in a geology class — very briefly the three types of rocks are:

  • Igneous — they form from the cooling of magma deep inside the earth. They often have large crystals (you can see them with the naked eye).
  • Metamorphic — they are formed through the change (metamorphosis) of igneous and sedimentary rocks. They can form both underground and at the surface.
  • Sedimentary — they are formed through the solidification of sediment. They can be formed from organic remains (such as limestone), or from the cementing of other rocks.
    Now the long story, which is much more interesting, is this:

Now, the long story, which is much more interesting, is this:

Igneous Rocks

Lava flow on Hawaii. Lava is the extrusive equivalent of magma. Image via Wiki Commons.

Magma is the heart of any igneous rock. Magma is composed of a mixture of molten or semi-molten rock, along with gases and other volatile elements. As you go deeper underground, the temperature rises; go further and you’ll eventually reach the Earth’s mantle — a huge layer of solid rock surrounding the Earth’s core (which, in geologic time, behaves as a viscous liquid).

As you probably know, when magma cools, it turns into rock; if it cools while still underground at high temperatures (but at temperatures still lower than that of the magma), the cooling process will be slow, giving crystals time to develop. That’s why you see rocks such as granite with big crystals — the magma had time to cool off. The crystals are also differentiated, as you can see below.

Note the white, almost rectangular feldspar crystals, the grey virtually shapeless quartz crystals, and the black crystals, which can be either black mica or amphibole. Image modified from Eastern Illinois University.

Note the white, almost rectangular feldspar crystals, the grey virtually shapeless quartz crystals, and the black crystals, which can be either black mica or amphibole. Image modified from Eastern Illinois University.

However, if the magma erupts or is cooled rapidly, you instead get a volcanic rock – not really igneous, but also originating from lava. The classical example here is basalt, which can have many small crystals or very few large ones. Volcanic rocks are also called extrusive igneous rocks, as opposed to intrusive igneous rocks. Some volcanic rocks (like obsidian) don’t have any crystals at all.

Basalt — note the almost complete lack of visible crystals. Now compare it to the granite. Image via Georgia State University.


Not all magma is made equally: different magmas can have different chemical compositions, different quantities of gases and different temperature — and different types of magma make different types of rocks. That’s why you get incredible variety. There are over 700 hundred types of igneous rocks, and they are generally the hardest and heaviest of all rocks. However, volcanic rocks can be incredibly lightweight – pumice, for example, can even float, and was called by ancient sailors “the foam of the sea”. Pumice is created when a volcano violently erupts, creating pockets of air in the rock. The most common types of igneous rocks are:

  • andesite
  • basalt
  • dacite
  • dolerite (also called diabase)
  • gabbro
  • diorite
  • peridotite
  • nepheline
  • obsidian
  • scoria
  • tuff
  • volcanic bomb

Metamorphic Rocks

Here, the name says it all. These are rocks that underwent a metamorphosis; they changed. They were either sedimentary or igneous (or even metamorphic), and they changed so much, that they are fundamentally different from the initial rock.

Different types of metamorphism. Image via Tankon Yvtar.

There are two types of metamorphism (change) that can cause this:

  • contact metamorphism (or thermal metamorphism) — rocks are so close to magma that they start to partially melt and change their properties. You can have recrystallization, fusing between crystals and a lot of other chemical reactions. Temperature is the main driver here.
  • regional metamorphism (or dynamic metamorphism) — this typically happens when rocks are deep underground and they are subjected to massive pressure — so much so that they often become elongated, destroying the original features. Pressure (often times with temperature) is the main driver here.

Folded foliation in a metamorphic rock from near Geirangerfjord, Norway. Image via Wiki Commons.

Metamorphic rocks can have crystals and minerals from the initial rocks as well as new minerals resulting from the metamorphosis process. However, some minerals are clear indicators of a metamorphic process. Among these, the most usual ones are garnet, chlorite, and kyanite.

Equally as significant are changes in the chemical environment that result in two metamorphic processes: mechanical dislocation (the rock or some minerals are physically altered) and chemical recrystallization (when the temperature and pressure changes, some crystals aren’t stable, causing them to change into other crystals).

Marble is a non-foliated metamorphic rock.

They can be divided into many categories, but they are typically split into:

  • Foliated metamorphic rocks — pressure squeezes or elongates the crystals, resulting in a clear preferential alignment.
  • Non-foliated metamorphic rocks — the crystals have no preferential alignment. Some rocks, such as marble (the metamorphized version of limestone), are made of minerals that simply don’t elongate, no matter how much stress you apply.

Metamorphic rocks can form in different conditions, in different temperatures (up to 200 °C) and pressures (up to 1500 bars). By being buried deep enough for a long enough time, a rock will become metamorphic. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion; they can also form when the rock is heated up by the intrusion of magma from the Earth’s interior.

The most common metamorphic rocks are:

  • amphibolite
  • schist (blueschist, greenschist, micaschist, etc)


    A micaschist. The dark brown rounded minerals are garnet, and everything you see with a whiteish tint is the mica. The reddish areas are rusty mica. Image modified from Willowleaf Minerals.

  • eclogite
  • gneiss
  • hornfels
  • marble
  • migmatite
  • phyllite
  • quartzite
  • serpentinite
  • slate

Sedimentary Rocks

Sedimentary rocks are named as such because they were once sediment. Sediment is a naturally occurring material that is broken down by the processes of weathering and erosion and is subsequently naturally transported (or not). Sedimentary rocks form through the deposition of material at the Earth’s surface and within bodies of water.

A conglomerate — a rock made from cemented gravel. Image via Earth Physics Teaching.

Sedimentary rocks are quite difficult to classify, as they have several different defining qualities (the chemical make-up, the sedimentation process, organic/inorganic material), but the most common classification is the following:

  • clastic sedimentary rocks — small rock fragments (many silicates) that were transported and deposited by fluids (water, bed flows). These rocks are further classified by the size and composition of the clastic crystals included in the sedimentary rocks (most often quartz, feldspar, mica and clay).
  • conglomerates (and breccias)  conglomerates are predominantly composed of rounded gravel, while breccias are composed of angular (sharper) gravel.
  • sandstones  as the name says, it’s a rock made from many-sand-sized minerals and rock grains. The most dominant mineral in sandstone is quartz because it is the most common mineral in the Earth’s surface crust.

    An old, red sandstone. Image via Ian Hopkinson.

  • mudrocks  again, the name says it all — they’re rocks made from solidified mud. They typically contain very fine particles and are transported as suspended particles by turbulent flow in water or air, depositing once the flow settles.
  • biochemical rocks — you’ll probably be surprised to find out that most limestone on the face of the Earth comes from biological sources. In other words, most limestone you see today comes from the skeletons of organisms such as corals, mollusks, and foraminifera. Coal is another example of biochemical rock.
  • chemical rocks — these rocks include gypsum and salt (halite) and are formed mostly through water evaporation

Yes, salt is a mineral — and it can be quite beautiful. In this context, it’s called halite and can be classified as a sedimentary rock.

There are also other types of specific sedimentary rocks for example, the ones formed in hot springs. Most of the solid surface of our planet (roughly 70%) is represented by sedimentary rocks, but if you go deep enough beneath the Earth’s surface, there are plenty of igneous and metamorphic rocks to be found.

As I mentioned with biochemical rocks, fossils can become rocks in time. You can actually have entire mountains made up from reefs like you can see below.

This entire mountain in Romania was formed based on a coral reef. Image via MP Interactiv

Some common sedimentary rocks are:

  • argillite
  • breccia
  • chalk
  • chert
  • claystone
  • coal
  • conglomerate
  • dolomite
  • limestone
  • gypsum
  • greywacke
  • mudstone
  • shale
  • siltstone
  • turbidite

This is just scratching the surface you could spend a lifetime studying rocks and still be surprised. But I hope that for your general knowledge or to impress some friends (or if you’re considering starting geology), the information here was useful and interesting to you. Feel free to send any questions and comments my way and I’ll do my best to answer them!

Evidence of 3.5-Billion-Year-Old Bacterial Ecosystems Found

To say that finding evidence of how life on Earth was 3.5 billion years ago is hard would be an understatement. Reconstructing the rise of life in its early stages is a monumental challenge – the evidence is only preserved in Earth’s oldest sedimentary rocks, and sedimentary rocks of that age are very hard to come by. However, a new study revealed the well preserved remnants of a complex ecosystem in a nearly 3.5 billion-year-old sedimentary rock sequence in Australia.

life australia

A rock surface is displaying “polygonal oscillation cracks” in the 3.48 billion years old Dresser Formation, Pilbara region, Western Australia. Such and similar sedimentary structures are of biological origin.

The study was conducted by a team which included Carnegie’s Nora Noffke, a visiting investigator, and Robert Hazen, a research scientist at the Carnegie Institution of Washington’s Geophysical Laboratory.

The Pilbara district of Western Australia is geologically speaking one of the most spectacular areas in the world. Scientists have described in detail deposits created by ancient photosynthetic bacteria, called stromatolites, and microfossils of bacteria – a very rare insight into that ancient world. However, one piece of the puzzle lacked from the Pilbara district: a phenomenon called microbially induced sedimentary structures, or MISS, had not previously been seen in this region. These structures are formed from mats of microbial material, much like mats seen today on stagnant waters, be they mainland or oceanic coastal lines. In other words, microbially induced sedimentary structures are primary sedimentary structures formed by the interaction of microbes with sediment and physical agents of erosion, deposition, and transportation.

But now, the team of geologists managed to locate this phenomenon in the old rocks, confirming their initial results with advanced chemical tests. The MISS was found in a formation called the Dresser Formation, and it strongly resembles a similar structure, dated 2.9 billion years ago.

“This work extends the geological record of MISS by almost 300 million years,” said Noffke, who is also a professor at ODU. “Complex mat-forming microbial communities likely existed almost 3.5 billion years ago.”

The team suggests that the bacterial mats were formed as a result of the interaction between the interactions of bacterial films with shoreline sediments from the region.

“The structures give a very clear signal on what the ancient conditions were, and what the bacteria composing the biofilms were able to do,” Noffke said.

Studying MISS is very important, because they are among the main targets for the Mars rovers. Thus, these results could have significant implications for studying life on other places in our solar system.

Journal Reference:

  1. Nora Noffke, Daniel Christian, David Wacey, Robert M. Hazen. Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in theca.3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia.Astrobiology, 2013; 131108054848000 DOI:10.1089/ast.2013.1030

Jurassic records warn of risk to marine life from global warming

The massive, global risk that global warming poses has once again been highlighted by researchers – this time, by geologists studying fossil records.

Fossil ammonites analyzed in the study. Ammonites are an extinct group of vertebrates that lived 400 to 65 million years ago.

Fossil ammonites analyzed in the study. Ammonites are an extinct group of vertebrates that lived 400 to 65 million years ago.

It’s good to learn from your mistakes, but it’s even better to prevent than treat, and learn from the past (even though it’s not your past) – and paleontology is really good at this. After all, we have over billion years of fossil evidence of life (though “only” a few hundred millilon years of evolved life). Ancient geologic evidence doesn’t only preserve animal information, but also climatic and environmental changes, as well as all sorts of other useful information.

Now, researchers from Plymouth University have shown how higher temperatures and lower oxygen levels caused drastic changes to marine communities, and that even though the Jurassic seas eventually recovered from the effects of global warming, the marine ecosystems that returned were noticeably different from before.

Professor Richard Twitchett, from the University’s School of Geography, Earth and Environmental Sciences, and a member of its Marine Institute, explained:

“Our study of fossil marine ecosystems shows that if global warming is severe enough and lasts long enough it may cause the extinction of marine life, which irreversibly changes the composition of marine ecosystems.”

He analyzed marine sedimentary rocks and the fossils they contained – which provided information about the environment in which the rocks were deposited and the creatures lived. After this, working with Dr Crispin Little from the University of Leeds, they correlated their initial results with other ecological data, ultimately reaching some conclusions on changes in temperature, sea level and oxygen concentrations.

“Back in the laboratory, we broke down the samples and identified all of the fossils, recording their relative abundance much like a marine biologist would do when sampling a modern environment. Then we ran the ecological analyses to determine how the marine seafloor community changed through time.”

Most notably, the team found a ‘dead zone’ recorded in the rock – showing virtually no evidence of fossils. After this period ended, the emerging life forms were much different than those initially there.

“The results show in unprecedented detail how the fossil Jurassic communities changed dramatically in response to a rise in sea level and temperature and a decline in oxygen levels. Patterns of change suffered by these Jurassic ecosystems closely mirror the changes that happen when modern marine communities are exposed to declining levels of oxygen. Similar ecological stages can be recognised in the fossil and modern communities despite differences in the species present and the scale of the studies.”

So basically, a significant change in environmental conditions will dramatically affect marine life, and even if it bounces back eventually, we’re talking about an entirely different equilibrium, and entirely different species. Also, another thing that’s worth noting is that the fact that this change took place in geologic time – millions of years; this is definitely something worth keeping in mind, as we are doing comparable changes to environment in hundreds or even tens of years – changes which will most likely change the fact of the Earth as we know it.