A very interesting Dendrology study site: http://www.public.iastate.edu/~bot356/
Images are from: http://en.wikipedia.org/wiki/Dendrology Dendrology (Ancient Greek: δένδρον, dendron, "tree"; and Ancient Greek: -λογία, -logia, science of or study of) or xylology (Ancient Greek: ξύλον, ksulon, "wood") is the science and study of wooded plants (trees, shrubs, and lianas). There is no sharp boundary between plant taxonomy and dendrology. However, woody plants not only belong to many different plant families, but these families may be made up of both woody and non-woody members. Some families include only a few woody species. This severely limits the usefulness of a strictly dendrological approach. Dendrology tends to focus on economically useful woody plants, their identification and horticultural or silvicultural properties. Fossil wood is wood that is preserved in the fossil record. Over time the wood will usually be the part of a plant that is best preserved (and most easily found). Fossil wood may or may not be petrified. The study of fossil wood is sometimes called palaeoxylology, with a "palaeoxylologist" somebody who studies fossil wood. The fossil wood may be the only part of the plant that has been preserved, with the rest of the plant completely unknown:[1] therefore such wood may get a special kind of botanical name. This will usually include "xylon" and a term indicating its presumed affinity, such as Araucarioxylon (wood of Araucaria or some related genus),Palmoxylon (wood of an indeterminate palm), or Castanoxylon (wood of an indeterminate chinkapin).[2] Types[edit]Petrified wood[edit]Main article: Petrified wood Petrified wood are fossils of wood that have turned to stone through the process of permineralization. All organic materials are replaced with minerals while maintaining the original structure of the wood. The most notable example is the petrified forest in Arizona.[3] Mummified wood[edit]Mummified wood are fossils of wood that have not permineralized.[1] They are formed when trees are buried rapidly in dry cold or hot environments. They are valued in paleobotany because they retain original cells and tissues capable of being examined with the same techniques used with extant plants in dendrology.[4] Notable examples include the mummified forests in Ellesmere Island[5] and Axel Heiberg Island.[6] Submerged forests[edit]Main article: Submerged forest Submerged forests are remains of trees submerged by marine transgression. They are important in determining sea level rise since the last glacial period.[
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The following is a cool image from http://drilllab.com, the entire ocean and seafloor is condensed in a beaker, with a drill ship floating on the very top. This has a lot to do with my research interest, something to do with the natural resources being produced millions of years ago, and its environmental impact occurring today, due to the perturbation of C cycle at a rate faster than ever! I think I got the web address of drill lab from Goldschmidt this June in Sacramento, CA.
Exercise 1:
The following are research questions derived from an NSF-funded proposal: Expansion and Collapse of the Cordilleran Ice Sheet during the Quaternary. As we can now reconstruct previous glacial cycles, there are a number of exciting hypotheses that can be tested using deep sea cores off the Vancouver Margin. The following questions cannot presently be answered, and moreover are unlikely ever to be answered by terrestrial investigation alone: 1. When was glacial activity confined to mountain glaciers during the Last Glacial Maximum? When were icebergs discharged? 2. When did the ice sheet begin to grow during the Last Glacial? Was it in phase or out of phase with global climate change? 3. Was there a lead/lag relationship between sea surface temperature change and ice sheet collapse? 4. Can MD02-2496 be used as a ‘Rosetta Stone’ for deciphering past Cordilleran Ice Sheet history? 5. Did the position of the Aleutian Low control the build-up of the southern Cordilleran Ice Sheet? What does this tell us about the state of the jet stream during ice sheet growth/decay? We would test these hypotheses by determining the flux of glacial sediment during the Last Glacial Maximum, and timing of IRD delivery and turbidite activity. Furthermore data including organic carbon content as well pollen and dinaflagellate populations will be provided by international collaborators Thomas Pedersen at the University of Victoria and Ann de Vernal at UQAM that will assist with constraining local climate conditions. Dating of the events would be completed through 14C dating and a careful age model determination where instantaneous events such as turbidites are methodically removed. Once the relationships between sediment lithofacies, particle size and Cordilleran Ice Sheet behavior is understood, then we will use ODP Site 888 to extend the history of the Cordilleran Ice Sheet before the Last Glacial Maximum, perhaps back 500kyr BP. We will determine local sea surface temperature changes from planktonic d18O and global ice volume from benthic d18O. We will then compare local SSTs with ice sheet buildup/decay to determine when increased delivery of precipitation was occurring, and therefore when the jet stream was deflected south over Vancouver Island. Here is a glance at how does GEOCARB work:
The following picture is a feedback diagram showing how Ca and Mg silicates weathering is positively affected by temperature and rainfall/runoff, hence draw down atmospheric CO2, leading to lower temperature and close the negative feedback loop (Picture modified from Berner, 2004). http://www.geology.sdsu.edu/how_volcanoes_work/intraplvolc_page.html Part 1: Here is how volcanic CO2 degassing works for Intraplate volcanism, also known as hotspot. Although most volcanic rocks are generated at plate boundaries, there are a few exceptionally active sites of volcanism within the plate interiors. These intraplate regions of voluminous volcanism are called hotspots. Twenty-four selected hotspots are shown on the adjacent map. Most hotspots are thought to be underlain by a large plume of anomalously hot mantle. These mantle plumes appear to be generated in the lower mantle and rise slowly through the mantle by convection. Experimental data suggests that they rise as a plastically deforming mass that has a bulbous plume head fed by a long, narrow plume tail. As the head impinges on the base of the lithosphere, it spreads outward into a mushroom shape. Such plume heads are thought to have diameters between ~500 to ~1000 km. Many scientists believe that mantle plumes may be derived from near the core-mantle boundary, as demonstrated in this computer simulation from the Minnesota supercomputing lab. Note the bulbous plume heads, the narrowplume tails, and the flattened plume heads as they impinge on the outer sphere representing the base of the lithosphere. Decompressional melting of this hot mantle source can generate huge volumes of basalt magma. It is thought that the massive flood basalt provinces on earth are produced above mantle hotspots. Although most geologists accept the hotspot concept, the number of hotspots worldwide is still a matter of controversy. HOTSPOT TRACKSThe Pacific plate contains several linear belts of extinct submarine volcanoes, called seamounts, an example of which is the Foundation seamount chain shown here. The formation of at least some of these intraplate seamount chains can be attributed to volcanism above a mantle hotspot to form a linear, age-progressive hotspot track. Mantle plumes appear to be largely unaffected by plate motions. As lithospheric plates move across stationary hotspots, volcanism will generate volcanic islands that are active above the mantle plume, but become inactive and progressively older as they move away from the mantle plume in the direction of plate movement. Thus, a linear belt of inactive volcanic islands and seamounts will be produced. A classic example of this mechanism is demonstrated by the Hawaiian and Emperor seamount chains.
The "Big Island" of Hawaii lies above the mantle plume. It is the only island that is currently volcanically active. The seven Hawaiian Islands become progressively older to the northwest. The main phase of volcanism on Oahu ceased about 3 million years ago, and on Kauai about 5 million years ago. This trend continues beyond the Hawaiian Islands, as demonstrated by a string of seamounts (the Hawaiian chain) that becomes progressively older toward Midway Island. Midway is composed of lavas that are ~27 million years old. Northwest of Midway, the volcanic belt bends to the north-northwest to form the Emperor seamount chain. Here, the seamounts become progressively older until they terminate against the Aleutian trench. The oldest of these seamounts near the trench is ~70 million years old. This implies that the mantle plume currently generating basaltic lavas on the Big Island has been in existence for at least 70 million years! The Hawaiians were very good at recognizing the difference in the older, eroded volcanic islands and newer islands to the southeast, where volcanic features are more pristine. Legend has it that Pele, the Hawaiian goddess of fire, was forced from island to island as she was chased by various gods. Her journey is marked by volcanic eruptions, as she progressed from the island of Kaua'i to her current home on the Big Island. The legend corresponds well with the modern scientific notion of the age progression of these volcanic islands. The reason that I'm interested in these volcanoes is the CO2 released from them. Current estimates of CO2 release rate from hotspot volcanoes range from 0.5 to 3 x10^18 mol/my. This is 0.006 to 0.036 Pg C/yr (Gt C/yr), only a small fraction of the current fossil fuel burning rate 10 Gt C/yr today!
The other form of volcanic CO2 release is through release from mantle at mid-ocean ridge, that is 1 to 3 x10^18 mol/my, similar to that of hotspot CO2 release. There is also release in arc volcanoes from subducted CaCO3 (turns out to be the largest 2 to 3 x10^18 mol/my), and release in arc volcanoes from the mantle (very small, 0.3 to 0.5 x10^18 mol/my). All these add up to a total global degassing of 4 to 10 x10^18 mol/my. Unless my calculation is wrong, this equals to 0.048 to 0.12 Gt C/yr CO2 release rate. This is a simple mass balance calculation, and without our anthropogenic CO2 emission, this is perhaps the rate of CO2 is released in natural system, but this CO2 is balanced by silicate weathering occurring on land. So the net CO2 release from volcanoes is essentially 0!!! The Phanerozoic pCO2 and pO2 has been elegantly calculated by Dr. Robert Berner using a long-term C cycle model called GEOCARB. The fundamental of the model is that silicate weathering acts as a negative feedback to the climate system, i.e. as pCO2 level goes up, more silicate weathering, hence drawing down pCO2. Feedback loops within the dynamic system defined by tectonics, climate and erosional surface processes. There are two feedback loops; a direct path (I) whereby tectonics increases erosion rates by increasing elevation, relief and drainage basin areas and an indirect loop (II), whereby increased elevation induces increased erosion rates through changes in climate. Climate change is in the form of enhanced precipitation or lower temperatures, which lead to glaciation. In each case, there is feedback in the tectonic response to surface mass redistribution. More complex processes and pathways are likely to exist.
Some related knowledge is described here: http://pangea.stanford.edu/~dpollard/NSF/main.html
We all know that there are "big five" extinction events in Earth history, today I want to focus on the largest extinction of all time, the end-Permian extinction event.
The following images are courtesy to BBC Nature, and some of my own research. First of all, what is Permian? According to BBC Nature, the Permian is defined as the following: Permian period: The Permian started with an ice age and ended with the most devastating mass extinction the Earth has ever experienced. In fact, at least two mass extinctions occurred during this time. It's also when all the continents of the world finally coalesced into one supercontinent, named Pangaea (meaning 'the entire Earth'). As the globe warmed up and the ice retreated, many areas of Pangaea became very arid. The oxygen level plummeted too, from a high of 35% of the total atmosphere to around 15%. For comparison, today's oxygen content is 21%. (I have doubts about the above assertion of oxygen levels, more information on Late Permian oxygen levels, see my recent work on oxygen during the end-Permian mass extinction, an Earth system modeling perspective). The webpage for the images below is: http://www.bbc.co.uk/nature/history_of_the_earth/Permian#intro |
Ying CuiI'm a geoscientist doing research on extreme environmental change and its impact to biodiversity in the geologic past. ArchivesCategories |