Archive for the ‘Field Work’ category

MarsSed 2010 Field Trip Day 2: Stromatolites, Gypsum and Layers

April 29, 2010

We started off Day 2 of the field trip by driving up onto the eroded rocks of what used to be the tidal flats of the ancient reef, between the shore and the continental shelf. The closest modern-day analog to the rocks that we visited is the Persian Gulf, where you have an arid climate and deposition on the shelf and down into the deeper ocean basin. In the tidal flats and lagoons of the ancient sea where the rocks that we visited formed, the water was only a few meters deep, and was a nice place for blue-green algae to grow. You might think that a bunch of single-celled organisms wouldn’t leave much of a mark in the geologic record, but you would be wrong!

The wavy layers in the carbonate rocks here are stromatolites - fossil backterial mats that grew in the shallow tidal flats and lagoon behind the ancient reef.

In fact, cyanobacteria growing in tidal flats tend to form thick, wavy mats that are then preserved and fossilized, forming “stromatolites”. Stromatolites are among the oldest evidence of life on the Earth. We spent quite a while discussing the stromatolites here, and particularly learning how to tell the difference between wavy layers that are biogenic and those that are due to things like sand ripples or deformed layers that were originally flat. The variation of the layer thickness is the first hint: stromatolites tend to be thicker in low points and thinner in high points. If the waviness was due to the deformation of originally flat layers, there shouldn’t be a change in thickness between highs and lows. Another hint is if you can tell that the waviness forms domes rather than parallel ridges, and especially if you find isolated domes or columns. It’s difficult to form an isolated dome-shaped ripple, but that’s exactly what you get when mounds of cyanobacteria are growing.

Modern stromatolites growing in Shark Bay, Australia. Original image by Paul Harrison.

After looking closely at stromatolites, we drove closer to what was the ancient shore and encountered an abrupt transition to layered gypsum and silt beds deposited as the near-shore pools periodically dried out. This area was used as the “slow-motion” field test for Mars Science Laboratory in 2007. The science teams essentially practiced by sending someone out here to take pictures and samples, and the team tried to understand the site without any other information. For our field stop, we took a look at some infrared maps of the minerals in the area, and then climbed a nice exposure of them.

We climbed "Tepee Hill", a nice exposure of gypsum and mudstone layers deposited in the evaporative shelf lagoon.

In the afternoon, we drove to “Last Chance Canyon” to admire an excellent exposure of the inclined beds that characterize the transition from the continental shelf to the ocean basin. The curves of the canyon let us see the tilted layers from different angles to get a good three-dimensional feel for the stratigraphy. We spent a while sitting up on one side of the canyon and sketching the opposite side and then hearing from our expert guides about all the subtle details that we amateurs had missed in our sketches.

The upper layers here are flat-lying, but below them, the layers begin to dip down to the right. These dipping beds were deposited on the slope of the shelf margin. Don't be fooled by the diagonal dark green vegetated stripes that go from upper right to lower left - those are fractures in the rocks where plants have taken hold.

It started to rain while we were studing the outcrop, but lucky for one member of our group, he was carrying the large canvas print-out of the Burns formation, a well studied section of rocks on Mars. Turns out it makes a decent cloak.

Our penultimate stop of the day was not listed in the guidebook but was pretty interesting. We took a look at some of the carbonate layers that had curious features called “tepee structures”. The leading theory for how these structures form is that, when carbonate deposits dry out, new minerals form and cause the layers to expand, causing them to buckle upward. There’s still a lot of debate about how they formed, however. They’re interesting to us martians because in an overhead view, the buckled zones form polygons, and there are polygonal features all over on mars.

A good example of a "tepee structure" is visible in the rocks here, just right of center. Geologists aren't completely sure how they form but the leading theory is that it has something to do with the rocks expanding as they dry out and new crystals form.

Our final stop was also not listed in the guidebook. We decided that since we had been talking about the ancient reef so much that we should take a look at it. Within the carbonates of the reef we found a lots of interesting fossils, including a texture that looked like miniature stromatolites, large spiral shells, and crinoid remains.

That concludes Day 2 of the field trip! Day 3 was a visit to Carlsbad Caverns – stay tuned for lots of pretty pictures!

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MarsSed 2010 Field trip – Day 1: Guadalupe Mountains and Evaporites

April 26, 2010

Hello everyone, I’m back from the MarsSed 2010 meeting in ElPaso! The meeting was great: it was small and focused on sedimentology and stratigraphy on Mars, with lots of room for discussion. Even better, there were plenty of terrestrial geologists attending, and their comments were extremely helpful for me, and probably many other Martians who lack a geology background.

After two and a half days of presentations and discussion (and a lot of learning on my part), we headed off on our field trip to the Guadalupe Mountains!

We started off in a salt flat graben with a lovely view of the Guadalupe mountains. What’s a graben, you say? It is a low-lying block of land, bordered by parallel faults. If you have heard of the “basin and range” region of the southwestern US, then the basins are graben. The mountain ranges are also called “horsts”.

A nice diagram of horsts and graben. This is how the "basin and range" area of the southwest formed.

The graben that we stopped in was a salt flat, where gypsum and halite are left behind when water collects in the lowlands and then dries out.

A view of the Guadalupe Mountains from the salt flat.

From our vantage point, we studied the nicely exposed mountains and compared them to a detailed cross-section of the area. The rocks of the mountains were once a large carbonate reef on a continental shelf. When sea level was high, thick carbonate beds were deposited on the slope of the continental shelf, and when sea level fell, sand and silt from the continent  were transported across the reef and deposited in the floor of the ocean basin. Here is a nice illustration that we found at one of the national park exhibits on the last day that really helped clear things up for me.

A diagram showing the relationship between the geographic setting and the underlying stratigraphy of the shelf and reef.

Here we are on the salt flat taking our first look at the stratigraphic cross section of the Guadalupe mountains. The mountains are off to the right, outside the field of view of this picture.

You may wonder what the relevance of ancient ocean reefs are for a bunch of Mars scientists. Fair enough. Nobody claims that we would find a big carbonate reef on Mars. Believe me, scientists have been searching for carbonates on Mars for decades. Recently, some small amounts have been detected, but nothing comparable to a huge reef. We were instead studying the reef as an example of a well-understood stratigraphy on Earth, and trying to learn how that stratigraphy was deduced. One of the main lessons was that not everything starts as a flat-lying layer! In fact, the edge of the reef appears to form a nearly horizontal layer, but it is actually made up of multiple sequences building outward into the basin. It just seems to form a layer because the reef always forms at the edge of the continental shelf. You can sort of see this “fake” layer in the pictures above. It is dark blue in the colorful cross section and is the light-toned band in cross section in the artist’s impression.

After discussing the cross section in some detail, and particularly admiring the large, inclined beds of the reef that were exposed in the mountains, we moved on to take a look at the deposits that filled the ancient Delaware basin when the sea began to dry out. The deposits have a very striking light and dark banding:

Layered evaporite deposits in the Castile Formation in the Delaware Basin. The light layers are gypsum, formed during the summer when evaporation rates were high, the dark layers are carbonate formed in the winter when evaporation was slower.

The light layers are gypsum and the dark layers are carbonate. The current theory is that each couplet represents one annual cycle: gypsum was deposited in the summer when evaporation was rapid, and carbonates were deposited in the winter. Apparently some poor graduate student counted all 260,000 couplets, which implies that it took about that many years to fill the basin with evaporites.

Something similar may have happened in the Mediterranean Sea more recently. It is thought that occasionally, the ocean level drops to the point where the Mediterranean is cut off from the Atlantic, and begins to dry out, depositing similar salts on its floor.

The relevance to Mars in this case is a lot more clear. There is evidence that many large craters were once filled with water. Now they are bone-dry, so presumably big evaporite deposits should be common on Mars! There are nice big stacks of hydrated sulfates at the bottom of Valles Marineris which might be remnants of such a deposit that precipitated out of a body of water in the canyon.

Stay tuned for Days 2 and 3 of the field trip! If you’re really interested, I suggest that you check out the awesome field guide that was made especially for our trip.

Off to MarsSed 2010

April 17, 2010

I’m headed off to El Paso Texas tomorrow! Why? Because that’s where the Mars Sedimentology and Stratigraphy workshop is! I’ll be presenting my work on the Gale Crater landing site for MSL on tuesday and then the second part of the week will be a geology field trip to interesting and instructive locations. I’m really looking forward to it, since the best way to learn geology is to go out and see it in person. Check out the awesome field guide that JPL put together for the trip:

The Painted Desert and Petrified Forest

March 22, 2009
The colorful layers of the painted desert formed in the triassic period when meandering tropical rivers deposted layers of mud and clay. Some of these layers are due to volcanic ash choking up the rivers and altering to clay.

The colorful layers of the painted desert formed in the triassic period when meandering tropical rivers deposted layers of mud and clay. Some of these layers are due to volcanic ash choking up the rivers and altering to clay.

(This is the final day of a week-long field trip in Arizona. Get caught up with days 1,2,3,4,5, 6)

Friday was the last day of the field trip, and we spent it at the Petrified Forest national park. We were there to study the colorful clays and river deposits, but we began the day with an unexpected bonus: our guide, Bill Parker, is a paleontologist at the park, and he took us to see some of the skeletons that have been found there, and the people who work on them. I spent much of my childhood wanting to be a paleontologist, so to actually see it in action was a special treat. We learned that there is recent evidence that almost all dinosaurs had feathers! We also got to see the reconstruction of what one of the animals may have looked like based on the skull, which was something that I didn’t realize that paleontologists did.

A paleontologist at Petrified Forest national park chips away at the protective plaster around the skull of an alligator-like dinosaur.

Matt Brown, a fossil preparer at Petrified Forest national park chips away at the protective plaster around the skull of an alligator-like dinosaur.

A reconstruction of what one of the dinosaurs may have looked like, based on its skull.

A reconstruction of what one of the dinosaurs being studied at the park may have looked like, based on its skull.

After the paleontology lab, we continued on to the painted desert badlands, which were the real reason we came to the park. These beautiful formations were formed when Arizona was a flat, tropical floodplain. Many of the layers are actually the deposits from broad, meandering rivers. When they overflow their banks, they deposit sediment in broad layers. In other cases, ash from volcanic eruptions blanketed the landscape, and was altered by the water of the lakes and rivers and rain to become clay minerals like bentonite. The clays expand when they get wet and contract when they dry, and are quite soft to begin with, so that it is very difficult for plants to get a foot-hold. This leads to broad expanses of “badlands” terrain: heavily eroded buttes and mounds of the brightly colored clays and sandstones.

The badlands terrain of the painted desert. The clays in the rocks expand when wet and contract when dry, creating an unstable surface where plants can't get a foothold. The bright colors are from different types of clay, different types of deposits, and different degrees of oxidation.

The badlands terrain of the painted desert. The clays in the rocks expand when wet and contract when dry, creating an unstable surface where plants can't get a foothold. The bright colors are from different types of clay, different types of deposits, and different degrees of oxidation.

We spent a long time studying an outcrop that used to be part of an ancient meandering river or delta. The layers deposited on the shore of a river tend to be angled in toward the riverbed, so by looking at the orientation of thelayers, you can guess at what the river might have looked like.

img_1537_smallClay-bearing river or delta deposits. These may have been deposited extremely rapidly, since there was the fossil of an 8-foot-tall horsetail in the outcrop, still standing upright and crossing several layers!

Clay-bearing river or delta deposits. These may have been deposited extremely rapidly, since there was the fossil of an 8-foot-tall horsetail in the outcrop, still standing upright and crossing several layers!

We were especially interested in this outcrop because we found fossils of giant horsetail plants in them, and the fossils were upright, as if they had been covered in sediment while still alive. That would mean that something like 8 feet of rock was deposited extremely rapidly, before the horsetail died and fell over! We speculated that this could happen during a particularly heavy monsoon season. In the layers with the horsetail there were also some very large rocks that were rounded as if they had been transported by the river.

One of our paleontologist guides, pointing at the two giant horsetail fossils. (click for full-resolution to see the fossils more clearly)

Jeff Martz, one of our paleontologist guides, pointing at the two giant horsetail fossils. Click for full-resolution to see the fossils more clearly.

A close-up of one of the horsetail fossils. The green part is a couple of inches across.

A close-up of one of the horsetail fossils. The green part is a couple of inches across.

After puzzling over the river deposits and trying to reconstruct their story, we ended the visit to the park by taking a look at the petrified forest. Our guide, Bill Parker, told us that all of the petrified trees in the park are missing their bark and branches, and that they likely were part of log jams in ancient Triassic rivers. He pointed out that it is almost impossible to find a modern river that hasn’t been modified by humans, and that in their natural state, these meandering rivers would have been clogged with dead trees. When the trees were buried by sand and ash, the silica in the rocks was dissolved in the water and precipitated out in the cells of the wood, gradually replacing organic matter with silica. The silica logs are much more resistant to erosion than the sandstone in which they are embedded, so as the rock erodes away, the logs are left sitting on the surface.

Petrified logs, formed when silica replaced the organic material of the wood, are more resistant to erosion than the sandstone in which they formed, and end up lying on the surface.

Petrified logs, formed when silica replaced the organic material of the wood, are more resistant to erosion than the sandstone in which they formed, and end up lying on the surface.

You may be wondering what all of this has to do with Mars. Well, the paleontology has very little to do, but the processes involved are quite relevant. Mars likely had liquid water in its past, and certainly had ash and sand deposits. Places like Mawrth Vallis have clay-bearing rocks eroded into channels and buttes and mounds, very similar to the clay-bearing rocks of the painted desert. The same conditions that prevailed to preserve the petrified forest and the dinosaur and plant fossils may also preserve more basic biomarkers, capturing evidence for a habitable Mars.

That concludes our geologic tour of Arizona! I went the first version of this trip two years ago, and then as now I was humbled by how complex and difficult to interpret our planet is, even when we can reach out and touch the rocks and analyze them at our leisure. On the other hand, there were many things that we saw from the ground that were much easier to interpret from aerial and satellite data. When you’re on the ground, it is much harder to get an feeling for the overall shape of what you are looking at. A combination of both orbital and ground-based studies is very important to really begin to understand the geology in detail, and even then there is a lot that we can’t figure out!

This trip has also impressed upon me how much more geology I need to learn. I need to know sedimentology and stratigraphy if I’m going to be attempting to read the story hidden in the layered pages of rock on Mars. But for now, I at least know what it is that I don’t know, and that’s a good start.

Grand Falls and Sand Dunes

March 20, 2009
An aerial view of Grand Falls and the dune field that we visited. Grand Falls is indicated by the marker. You can clearly see where lava blocked the previous course of the river.

An aerial view of Grand Falls and the dune field that we visited. Grand Falls is indicated by the marker. You can clearly see where lava blocked the previous course of the river.

(This is day 6 of a week-long field trip in Arizona. Get caught up with days 1,2,3,4,5)

Today we visited Grand Falls and the nearby dune field. Grand Falls is especially interesting because it combines many of the processes that are active in shaping planetary surfaces. The falls are the result of a huge lava flow pouring into the ancient canyon of the Little Colorado river, filling the canyon and flowing both up and downstream for many miles. Obviously this had quite an impact on the river! It formed a dam and a lake upstream until finally the lake spilled over the top of the lava dam and began carving a new course for the river. Basalts and other lava rocks are very hard compared to the Kaibab limestone and Moenkopi siltstones of the original canyon, so the huge tongue of lava is preserved, byt the river is currently working on carving a path around it in the softer rocks. The result is Grand Falls:

On the left you can see the dark, erosion resistant basalt that dammed the original canyon. On the right, Grand Falls are busy carving a new course for the river into the softer rock around the obstruction.

On the left you can see the dark, erosion resistant basalt that dammed the original canyon. On the right, Grand Falls are busy carving a new course for the river into the softer rock around the obstruction.

A mosaic of Grand Falls. Huge blocks of limestone sit at the bottom of the falls, showing that they are a powerful erosive force. (Click for full-resolution)

A mosaic of Grand Falls. Huge blocks of limestone sit at the bottom of the falls, showing that the falls are a powerful erosive force. (Click for full-resolution)

The other main point of interest at Grand Falls were the interesting patterns of cracks in the massive lava rock. These cracks, of “joints” tend to form perpendicular to surfaces in the flow that have the same temperature. In very simple flows, the joins often are vertical and the rock looks like it is made out of hexagonal columns. At Grand falls, the joints are mostly very jumbled, which probably means that steam was percolating through the rock as it cooled. This might mean that there was water in the river when the canyon was filled with lava (the Little Colorado doesn’t always have running water in it).

Columnar joints in the basalt flow at Grand Falls. This is one of the more ordered sets of joints; in many places there is no clear texture to the rock, suggesting complicated interactions with water as the lava cooled. Note that the normally-black basalt is stained tan-colored by the silt-bearing mist from the falls, yet more evidence that they are constantly eroding the rock that they flow over.

Columnar joints in the basalt flow at Grand Falls. This is one of the more ordered sets of joints; in many places there is no clear texture to the rock, suggesting complicated interactions with water as the lava cooled. Note that the normally-black basalt is stained tan-colored by the silt-bearing mist from the falls, yet more evidence that they are constantly eroding the rock that they flow over.

After Grand Falls, we drove our rental minivans through a shallow part of the river upstream, over some very rough roads, and arrived at a nearby dune field. This field is quite young: in the 1930s there were no dunes, but by the 1950s there were, and now no new dunes seem to be forming. The source of the sand is the bed of the Little Colorado, but there are also lots of dark volcanic cinders in the dunes. Larger gravel-sized particles get pushed around by small sand sized particles and form “granule ripples”. These are extremely common on Mars; the Opportunity rover is currently in the middle of an expansive plain of similar ripples.

Granule ripples. The larger, more dense basalt granules end up at the crest of the ripple, where finer-grained sand is blown away or settles below the granules. (in the background are the San Francisco Peaks, an extict stratovolcano)

Granule ripples. The larger, more dense basalt granules end up at the crest of the ripple, where finer-grained sand is blown away or settles below the granules. (in the background are the San Francisco Peaks and a few much smaller cinder cones)

Larger piles of sand form dunes. Dunes move as the wind blows sand up their slope and deposits it at the top until it becomes too steep and avalanches down the “slip face”. Here is an example of a boomerang-shaped “barchan dune” with a nice slip-face. This type of dune is very common on Mars.

A boomerang-shaped "barchan dune". The points, or "horns" of the dune point in the direction that the wind is blowing. In this image, the wind that formed the dune was blowing roughly from right to left.

A boomerang-shaped "barchan dune". The points, or "horns" of the dune point in the direction that the wind is blowing. In this image, the wind that formed the dune was blowing roughly from right to left.

That’s all for today. Tomorrow we will be visiting the painted desert, a location that may be similar to Mawrth Vallis on Mars, one of the potential MSL landing sites.

Meteor Crater, Walnut Canyon, and Red Mountain

March 19, 2009
Meteor Crater is the best preserved (and the first recognized) impact crater on Earth.

Meteor Crater is the best preserved (and the first recognized) impact crater on Earth.

(This is day 5 of a week-long planetary geology field trip to Arizona. Get caught up with days 1,2,3,4)

Today was a long and awesome day. We started out at meteor crater, the youngest and best preserved impact crater on Earth! Our guide today was Shaun Wright, a colleague from the Hawaii field workshop, among other places. He showed us infrared images of the crater taken from an airplane and we walked around the rim trying to identify the main compositions detected. Meteor crater is especially nice for this because it excavated into three distinct layers: the red Moenkopi siltstone (the surface of the surrounding plains), the yellowish Kaibab limestone (normally beneath the Moenkopi), and the white Coconino sandstone (below the Kaibab).

Back in the early 1900s, people were trying to dig and find the iron meteorite that they thought was buried under the crater. (it turns out the meteorite was blasted into thousands of pieces upon impact) Luckily, the mining work carved a notch in the rim that lets you see the three units of the crater where they have been overturned by the impact. When a large impact occurs, it lifts up the ground and forms an “overturned flap” at the rim. You can see in the picture that the Moenkopi goes from relatively solid-looking to very fractured-looking, and is then overlain by blocks of Kaibab and Coconino.

At the rim of the crater, the impact has reversed the sequence of layers. The red Moenkopi would normally be on top but here it is overlain by blocks of Kaibab limestone and Coconino sandstone that have been excavated by the impact.

At the rim of the crater, the impact has reversed the sequence of layers. The red Moenkopi would normally be on top but here it is overlain by blocks of Kaibab limestone and Coconino sandstone that have been excavated by the impact.

Another very interesting part of the crater is that the impact pulverized the coconino sandstone, crushing the sand grans into powder. This powder was actually mined for a while because it is a very high grade silica “rock flour” used in things like makeup. Amazingly enough, even though it has been subjected to one of the most violent forces imagineable, the crushed sandstone still maintains its original structure, and you can even see crossbeds preserved!

The shocked sandstone still preserved very fine cross-bedded layers, but can be crumbled into a power with your hand.

The shocked sandstone still preserved very fine cross-bedded layers, but can be crumbled into a power with your hand.

After Meteor Crater, we made a short stop at Walnut Canyon, where the Coconino sandstone is not shocked and the crossbeds are displayed prominently. Remember, cross-bedded layers typically form when sand dunes are lithified in place and turned into sand stone, preserving the layers within the dune. For  more info about crossbeds, check the USGS site about them.

Crossbeds at Walnut canyon are essentially fossilized sand dunes from when Arizona was a coastal desert. The direction that the layers are tilted tells us that the prevailing winds blew from north to south.

Crossbeds at Walnut canyon are essentially fossilized sand dunes from when Arizona was a coastal desert. The direction that the layers are tilted tells us that the prevailing winds blew from north to south, although the various sets of layers in this image actually reflect several wind directions.

Finally, after Walnut canyon we drove up to Red mountain, which is a cinder cone volcanoe that has been carved open by erosion. Not only does it give a great view of the interior structure of the cone, it also erodes into a very bizarre landscape that looks like it belongs in a Dr. Seuss book.

The interior of Red mountain cinder cone. The layers are from different stages of the eruption that deposited cinders with slightly different composition or weathering properites. The bizarre shapes are due entirely to erosion, mostly by water.

The interior of Red mountain cinder cone. The layers are from different stages of the eruption that deposited cinders with slightly different composition or weathering properites. The bizarre shapes are due entirely to erosion, mostly by water.

That’s all for today. Tomorrow we are off to Grand Falls and the nearby dune field!

The Grand Canyon

March 18, 2009

The Grand Canyon carves through layers of rock deposited over the past 1400 million years of earth's history.

Today we visited the Grand Canyon. If you haven’t been there before, there is no way to convey what it is like. It is the only place I’ve ever been with a view that literally took my breath away. John Wesley Powell, a one-armed civil war veteran and geologist wrote extensively about his pioneering voyages through the canyon and summed it up quite well:

“The glories and the beauties of form, color, and sound unite in the Grand Canyon – forms unrivaled even by the mountains, colors that vie with sunsets, and sounds that span the diapason from tempest to tinkling raindrop, from cataract to bubbling fountain.” … “The wonders of the Grand Canyon cannot be adequately represented in symbols of speech, nor by speech itself. The resources of the graphic art are taxed beyond their powers in attempting to portray its features. Language and illustration combined must fail.” – John Wesley Powell

The canyon is not just beautiful, it is also the world’s best exposure of layered rock, with layers stretching back in time 1.4 billion years. Our guide today was Ivo Lucchita, a geologist who has spent his whole career studying the canyon, and he told us the story that is hidden in the layers of the canyon. I will try to relay a little bit of it here.

The stratigraphic sequence of the Grand Canyon.

The stratigraphic sequence of the Grand Canyon.

The story begins 1.4 billion years ago as the North American continent was forming. The continental plate collided with an island arc (similar to Japan), and that collision compressed some of the rocks of the continent, folding the layers like an accordian and altering the minerals. This resulted in the Vishnu schist, which is the lowest layer of the canyon.

The schist was then planed off by erosion for thousands of square kilometers. You might wonder how erosion would carve rocks into a perfectly flat surface, but you can see it happening today anywhere that the ocean is crashing against steep cliffs. Waves only erode down to a certain depth, so as they eat away at sea cliffs, they create a flat erosional surface.

After that surface was planed off, a thick stack of layers was deposited in a wide variety of environments ranging from deep oceans to arid deserts. This was all during the proterozoic, when the only life was simple and single-celled. This stack of proterozoic layers is called the Grand Canyon supergroup, and ends with the Chuar group, which was laid down about 750 million years ago and contains fossils of the first blue-green algae. The proliferation of algae marked a significant transition for the earth because all that photosynthesis changed the atmosphere, enriching it in oxygen. The layers of the grand canyon supergroup are now tilted with repect to the rest of the overlying layers of the canyon, probably due to tectonics related to the early North American plate.

The red and white-striped eroded surface shown here near the river is teh tilted Grand Canyon supergroup, deposited over about a billion years during the proterozoic, prior to multicellular life.

The red and white-striped eroded surface shown here near the river is the tilted Grand Canyon supergroup, deposited over about a billion years during the proterozoic, prior to multicellular life. The flat shore near the bend in the river is one location that was settled and farmed by native americans a few thousand years BC.

After the proterozoic layers were tilted and eroded, most of the rest of the layers were deposited over the next half a billion years during the paleozoic. Once again, these layers represent wildly varying climates and settings, from oceans to deserts to floodplains, to shorelines. During the paleozoic, life became phenomenally sucessful, developing from algae into complex marine animals and amphibians.

The layers above the tilted lower strata were deposited between 545 and 260 million years ago during the paleozoic, during which time life advance from algae to amphibians.

The layers above the tilted lower strata were deposited between 545 and 260 million years ago during the paleozoic, during which time life advance from algae to amphibians.

The paleozoic ended with the great permian extinction, in which 98% of all species died off. After the paleozoic came the Mesozoic: the age of reptiles. Many more layers were deposited, but they have been eroded away again. The erosion stopped at the rim of the canyon because it is made of the very tough kaibab limestone.To find the mesozoic layers, you have to travel to the nearby painted desert.

More recently in the cenozoic, which began 65 million years ago with the extinction of the dinosaurs, and marks the beginning of the “Age of mammals”, there were more continent collisions, causeing the uplift of the Colorado plateau, and many faults and volcanoes. At some point, the direction of drainage in the area reversed, and the early Colorado river changed course to its present location.

Oddly enough it is not well understood exactly how the river ended up the way it is today. There are a lot of subtleties to the Colorado river that are quite confusing when considered with the vast changes in geography of the area over the last few million years. In any case the canyon is likely not that old compared to the rocks that it cuts, and may be as young as 4 million years old.

Finally, one of the most interesting things that we talked about today is the early settlement of the canyon by native people. Apparently a few thousand years ago the river carried a huge load of sediment, and actually behaved much like the Nile, with floods and the meandering course of the river in its bed crating fertile lands on the banks. Ivo told us about some studies of charcoal layers found in the soils of the river banks that also contained maize pollen, indicating that there was farming in the canyon at least 3094 BC! That’s the same time period in which Nebuchadnezzar ruled Egypt and Moses would have lived! Update: a friend of mine corrected me on this. I was trying to remember what Ivo said during our field trip and he in turn was remembering off the top of his head, so things got a bit jumbled. Here’s the real deal, which is actually even more impressive!

– Moses is usually placed (for example by Flavius Josephus) in either the reign of Ramesses II, or his predecessor, or his successor — at any rate one of the pharaohs of the 19th Dynasty.  The 19th Dynasty lasted from 1292 to 1190 BC, not 3094 BC.  3000 BC even predates the time of Abraham (~2000 BC or later — a lot of people like to place the story of Joseph, Abraham’s great-grandson, in the Hyksos period, around 1600 BC).

– Nebuchadnezzar  was a king of the Neo-Babylonian period.  Wikipedia gives his dates as 630 to 562 BC.  So that is even later than Moses…  Nebuchadnezzar led the Babylonians in a campaign against Egypt (then ruled by pharaohs of the 26th dynasty) but evidently did not succeed in conquering it.

If the Grand Canyon remains are really from the 31st century BC, then they are even older than the Pyramids.  They’d be roughly contemporary with Narmer and the Egyptian 1st Dynasty.

The Grand Canyon is amazing. The history of the earth is laid bare in front of you, and the story that it tells is as overwhelming in scale as the canyon itself.

I’ll finish with another quote from John Wesley Powell, which nicely summarizes the spirit of exploration and curiosity that drove Powell to risk life and limb to study the canyon. That same spirit resonates with those of us involved in exploring the solar system today:

We have an unknown distance yet to run, an unknown river to explore. What falls there are, we know not; what rocks beset the channel, we know not; what walls ride over the river, we know not. Ah, well! we may conjecture many things. -John Wesley Powell


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A late afternoon view down the canyon. The stretch of river visible is one of the largest rapids in the canyon and is about a mile long.