~30 million year old leaf impression fossils of plants from the Rujada Flora from a forest roadcut through the Fisher Formation near Cottage Grove, Oregon. Specimens include leaves of sumac (Rhus varians), alder (Alnus carpinoides), tanoak ( Notholithocarpus simulans), and dawn redwood (Metasequoia occidentalis)!

The Oligocene (~30 Ma) Rujada flora (42 spp.) and the nearby Willamette flora (40 spp.) are dominated by oak (Quercus consimilis) and alder (Alnus heterodonta). The occasional fossil salamander (Palaeotaricha oligocenica) and caddis fly cases of Metasequoia needles (ichnogenus Folindusia) have also been collected in the area.

These leaves fell into and were preserved in an ancient lake. Burial in lake sediments inhibited the decay of organic carbon in the leaves, which makes for exceptional preservation today. A recent roadcut exposed these ancient rocks. Thanks!

The study of paleobotany can help us understand how plants adapted to climate change millions of years ago, which can inform our predictions of how plants today may respond to modern climate change.

A few specimens acquired in the Amadeus Basin, near Alice Springs, Northern Territory, Australia, and range in age from ~380 Ma – 1 Ga.

Adrian Broz, Greg Retallack, Briony Horgan, Lucas Silva, and Matt Polizzotto

Sequence of ~33 million year old clay-rich fossil soils (paleosols) at the Painted Hills, John Day Fossil Beds National Monument, Oregon (Photo: Jamie Francis). These paleosols are similar in mineral composition (lots of hydrated clays) and  stratigraphic distribution to clay-rich areas on Mars at Mawrth Vallis, Nili Fossae, Oxia Planum, and elsewhere. Importantly, the ExoMars 2020 rover is going to Oxia Planum, which is a westward extension of the Mawrth Vallis clay layers.

Across ancient surface environments of Mars, Where are the best places to search for past signs of life? Where are you most likely to find something interesting, if it is there?

Mars offers the tantalizing prospect of being the most immediate and accessible location to test the hypothesis that life has existed elsewhere. Current and planned missions to Mars are investigating clay-rich areas (dioctahedral and trioctahedral phyllosilicate clay-rich rocks), but it is not well understood which types of clays (there are many types) are best at preserving organic matter or other biosignatures over geological time scales.

This research seeks to prioritize locations for in-situ biosignature detection (Curiosity and Mars 2020) and Mars Sample Return. Our approach is to examine clay-rich paleosols on Earth that are strikingly similar in clay mineralogy and stratigraphy to clay sequences that have been detected on Mars. Stay tuned for future updates.

                                                                             CLAY!

Sticky, slimy stuff….

Clays are cool because:

1) Their mineralogy can record the aqueous history of a given location by constraining the temperature, pH and water:rock ratio during clay formation.

2)  they have been implicated in many origin-of life theories (especially 2:1 phyllosilicates) because they facilitate spontaneous polymerization of complex macromolecules (like RNA) and provide the structural framework for concentration and preservation of these macromolecules;

and 3) They can preserve organic matter from oxidation and radiation, possibly over billions of years…

Why soil? Well..

(Source: Penn State Soil Characterization Lab)

10. Soil is forgiving….soil is a dynamic resource that can be restored and used again in the lifetime of a human.

9. Unless you live in a houseboat, your house is likely built on soil (even a houseboat is built from wood that came from a tree growing on soil).

8. Care for a beer? Not gonna happen without those plants that just happen to grow in soil.

7. Worried about global warming? Then be happy that soil sequesters about 2x the amount of carbon found in all vegetation and the atmosphere combined!

6. Cotton doesn’t just come from the mall…You get a lot of your clothes from crops that grow on soil.

5. Ever been sick? You probably have taken an antibiotic that was derived from organisms in the soil.

4. Ever drink water from a well or stream? You could likely die of contaminated water if there was not soil to filter water for drinking.

3. Enjoy eating? You would likely starve to death if you could not eat plants that grow in soil.

2. Like breathing? You probably would not be breathing if there was not soil for plants to grow in that produce the oxygen keeping you alive.

1. Imagine a world where nothing that died decomposed. Soil microorganisms are required for breaking down dead things on the surface of earth!

 

Soil lamellae are wonderful and striking features that form from a variety of processes.

They are typically seen in sandy, young soils or sediments.

The most frequent mode of formation is the downward movement of small clay particles and/or iron oxides.  Lamellae form as percolating soil-water carries small amounts of clay down a sandy soil profile .

 

From Mike Badzmierowski, Virginia Tech:

“Water infiltrating the soil will work its way down following the least resistive pathways. The boundary between soil that has been wetted and the unchanged soil is known as the wetting front. If the clay in suspension is near the edge of the wetting front, the clay will be deposited in a contorted initial lamella.” This deposited lamella may act as a filter for future wetting fronts, depositing clay particles and thickening in a snowball-type effect, but flattened into a layer instead of a ball or nodule.

 

The presence of lamellae in eolian and fluvial sediment deposits indicates marine sediments that are exposed to subaerial pedogenic conditions can turn a marine sediment into a poorly developed, sandy, young soil –  fairly rapidly. With  continued clay and iron oxide transport into  into lamellae layers over hundreds of years, a weakly-developed illuvial B – horizon is able to form (see picture below).

If you ever see soil lamellae when it is raining, get excited, because you are seeing  soil forming in front of you eyes!