#geologic timeline

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staffatrips Staffa looking spectacular in bright sun and with a big swell, July 2017.

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“Xenoconformity”

The term “unconformity” refers to a part of a sequence of sedimentary rocks where there is no sediment deposited. There are several types of unconformities – a nonconformity refers to a contact where sediments drape on top of igneous or metamorphic rocks, an angular unconformity refers to a boundary where rocks were tilted and partially eroded before new sediments were deposited, and a disconformity refers to a time within layers of sediment where deposition stops, but no changes can be easily recognized (https://tmblr.co/Zyv2Js1JtNUXH).

A recently published paper has proposed a new term for spots like this. This point is a GSSP, a “Global Boundary Stratotype Section and Point” where a single spot has been marked as containing a boundary on the geologic column. This point is at the start of the cap carbonate for the last proposed Snowball Earth glaciation, 640 million years ago. This GSSP point marks the start of the Ediacaran, a distinct period on the geologic timescale. The new paper proposes that a site like this should be called a “Xenoconformity”

Unconformities are, by definition, local changes. Rocks must be faulted or eroded or facies must change in a single area for it to be an unconformity. However, when big things happen – when global glaciations collapse, or there is an asteroid impact, sedimentation patterns change worldwide. When the asteroid struck the area that is now the Yucatan Peninsula at the end of the Cretaceous, sediment patterns changed literally on the opposite side of the world; the boundary has been recognized in places including Europe and North Africa.

That’s the type of boundary that scientist Alan Carroll at the University of Wisconsin proposes should be called a “Xenoconformity”. This term would distinguish local unconformities, as can be caused by small changes within a basin, from global events.

-JBB

Image credit: http://geology.geoscienceworld.org/content/45/7/671 Original paper: https://doi.org/10.1130/G38952.1

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Cut pyrite ichthyosaur Vertebrae

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Are these the world's oldest fossils?

In the sceptical world of science the adage is often repeated that exceptional claims require exceptional evidence, and these tiny needles of hematite (see http://bit.ly/2ctVrsX) found in some of Canada's older rocks (dated to between 3.77 and 4.28 billion years ago) have stirred up a healthy controversy in the early life community. They were found in ancient much metamorphosed cherts, near pure microcrystalline silica originally deposited as sinters in long gone hot springs, testimony to our planet's primeval volcanism.

The research team think that these features are the remnants of early bacteria or archaea that fed on chemical energy rather like the communities found around black smoker vents at oceanic spreading ridges today. If their absolute age is at the upper end of the date range it implies that life began very shortly after the Earth-Moon system formed and the first oceans condensed. The problem is simple, once one tries to reach back that far, there are very few rocks remaining that haven't been chewed up and recycled repeatedly in the rock cycle. Those that do remain have been repeatedly squished and baked in mountain building events, having repeated pulses of altering fluids pass through them along the journey through geological time, so any features within are difficult to interpret with confidence, rather like the bacteria in the still controversial Martian meteorite.

The Nuvvuagittuq supracrustal belt in Quebec contains some of the world's oldest rocks, and their features geochemistry implies a submarine vent formation since they seem to have both basaltic pillow laves and the remnants of the associated hydrothermal system. This environment has long been posited one of the potential places where chemistry and geology somehow turned into biology, so this formation is one of the few available suspects available for analysis.

Along with the shape (reminiscent of filamentous iron metabolising bacteria some half a millimetre long) the team suggest several other lines of evidence in favour of their hypothesis, including distinctive structures formed by several filaments linked together by a central blob of heamatite that are like bacterial communities living in similar places today and the presence of associated minerals including carbonate and apatite rosettes suggestive of past life. Spheroidal nodules are thought to be the remains of decayed bacteria and contain chemicals that are usually the result of putrefaction. Carbon isotopes are also suggestive of possible organic origin, since biological reactions are lazy by nature and favour the less energy intensive C12 isotope to the heavier C13, and select it preferentially out of the environment leading to an imbalance in the natural ratio.

Others have criticised the findings, pointing out that the uniform seeming orientation of the structures is very unlikely to be of organic origin, and suggesting that metamorphism was a more likely source. Others say that these structures are very large for a supposed life form so primitive, living in an energy restrictive anoxic environment. There have already been several false or still contested positives in this particular scientific quest.

Either way, these structures may remain inconclusive, but a lot of ongoing research is focussed on this question and those few remaining truly ancient rocks, both in order to understand the history and origin of this great mystery called life and to glean some impression of what might be possible on other planets in the solar system and beyond.

Loz

Image credit: 1: Matthew Dodd, 2: Dominic Papineau http://bit.ly/2lrU2qr http://bit.ly/2lYoRUR http://bit.ly/2mB5moO http://bit.ly/2mxkCCu http://bit.ly/2mxnAam Original article: http://go.nature.com/2lAvzUE

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Middle school students in California (who are probably almost graduating high school today) put together a video lesson on the geology of California, asking questions of experts about the history of the Earth, plate tectonics, deep time, and what is happening beneath their feet.

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Malaspina Glacier

Malaspina Glacier in southeastern Alaska is the quintessential illustration of a piedmont glacier. In fact, it is the world’s largest piedmont glacier — almost 65 kilometers wide and up to 45 kilometers long from the mountains to the edge of the sea. Piedmont glaciers are wide and bulb-shaped lobes that form when moving glaciers confined by mountain valleys spread out into a broad, flat plain. Malaspina Glacier was formed from the fusion of two valley glaciers — Agassiz Glacier on the left of the image and Seward Glacier from the right. To obtain this perspective view image of Malaspina Glacier, the scientists on the Shuttle Radar Topography Mission (SRTM) developed an elevation model and combined it with a Landsat satellite image. Shifting glaciers — how much glacial ice and snow accumulate or melt in a given period of time — are delicate barometers for global climate change. Observing glacial change is a task best suited from an aerial perspective, and since 1972, Landsat imaging has been the premier means for such a task.

-DC

Photo credit: http://1.usa.gov/1LOVBJF More reading: http://bit.ly/1KBbqn5 http://bit.ly/1G0xUFW

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If Jurassic Park had instead chosen different geologic eras

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I Believe In Evolution, Except For The Whole Triassic Period

I consider myself a rational person. When I have a question, I turn to science and logic to find the answer. Regarding the origins of life, science tells us that humans evolved from single-celled organisms to our current form through a process of natural selection that took billions of years.

This much is clear to anyone with any background in modern thinking. We can look at the fossil record and trace many of our genetic traits back to ancient species. In fact, scientific reasoning can explain nearly every stage of life from the Big Bang to the present day. I say "nearly" because the period that scientists claim lasted from roughly 205 to 250 million years ago, commonly known as the Triassic period, was quite obviously the work of the Lord God Almighty.

Classic Onion...headline that you stop and say “What the....”