(Visited 514 times, 1 visits today)FacebookTwitterPinterestSave分享0 Many inferences about past climate and evolution depend on a measurement with dubious interpretations.Two scientists just published a bombshell paper in PNAS that could undermine many inferences about past climate and evolution. Geyman and Maloof title their paper, “A diurnal carbon engine explains 13C-enriched carbonates without increasing the global production of oxygen.” Specialists in paleogeochemistry and paleoclimate should pay attention. Evolutionists should worry.Since nobody can observe the past in a time machine, scientists use proxies to make inferences about past conditions. A proxy is a measurement that theoretically traces what happened in the unobservable past. Examples are tree rings, stalactites, and isotopic ratios in sediments and ice cores. One proxy is particularly important, because it is widely trusted in everything from evolutionary theory to climate history. Its scientific shorthand is δ13C (delta-carbon-13), a measure of isotopic carbon ratios as they change over time (the Greek letter delta is shorthand for “change” in scientific lingo). Carbon, which is element 12 in the periodic table with 6 protons and 6 neutrons, has two famous isotopes. Carbon-14, with two extra neutrons, is unstable and radioactive, and used for ‘radiocarbon’ dating. Carbon-13 has one extra neutron. It is a stable isotope, but much less abundant than carbon-12. Because of its slightly heavier atomic weight, some processes can increase its abundance relative to carbon-12 in certain conditions. This is called fractionation: carbon-13 exhibits a higher fraction of total carbon than normal. One of these processes is photosynthesis.Crucially ImportantWhen geologists or climatologists see an “excursion” in δ13C in the sediment record, they want to know how it got there. Theories rush into the vacuum of the unknown. The most popular theory is that photosynthetic organisms concentrate carbon-13, such that inorganic carbon will have less of it than organic carbon. Why is this important?The δ13C of shallow carbonates is a crucially important tool for global chemostratigraphic correlation, especially before the appearance of index animal fossils.Based on measurements of sediments taken now, scientists routinely envision the chemistry of the oceans 500 million Darwin years ago and older. For example, they believe that rising oxygen in the oceans (inferred from δ13C measurements) triggered the Cambrian explosion. The extra oxygen “permitted” complex life to evolve after billions of years of low-oxygen water held them back (so goes the just-so story). Climatologists, too, use carbon-13 ratios to infer past climate conditions, teaching the peasants about geologic eras when temperatures were hot or cold, and when animals survived droughts and ice ages. A lot of interpretive weight is put on those carbon-13 excursions!Geyman and Maloof have a simpler explanation. It involves days, not millions of years. They identified a “diurnal cycle” that can enrich or deplete carbon-13 in shallow water sediments – the very locations where geologists typically measure it, or infer that the rock strata were formed in such sediments. (Deep marine sediments cannot be used because of plate tectonics and subduction.)We present stable carbon isotope (δ13C) data from modern carbonate sediment that require a decoupling of the carbon cycles in the global ocean versus shallow carbonate shelves. This realization is important because, for the first 97% of Earth history, many inferences about global paleoclimate and seawater chemistry rely on interpretations of shallow carbonates. We use modern observations and a simple model to show how ordinary diurnal carbon cycling in shallow waters is sufficient to produce anomalously positive δ13C on shelves today, and in the geological record. Our results alleviate the need to interpret positive δ13C excursions in the geological record as global reorganizations of the carbon cycle and instead link δ13C to local and/or global paleoenvironmental and paleoecological controls.If Geyman and Maloof are right, a good deal of interpretation about past climate and evolution could be vulnerable to falling like a house of cards.Evaluating the significance of this paper is going to take deeper analysis than is possible here. We want to bring it to the attention of non-Darwinian geologists in order to stimulate discussion and raise questions. Here are some possible questions:What are the extremes of interpretation involved? (i.e., no significance vs highly significant).What affect could this have on dating the geologic column?How does the new theory affect interpretation and dating of ice cores?What does it do to the interpretation of early earth conditions before fossils?How does it affect the theory of evolution?Laymen need to be cautious not to run off announcing a ‘scientific revolution’ regarding the age of the earth, climate, or the fossil record. When investigating a proxy like this, there are all kinds of complicating factors: e.g., the effects of temperature on deposition, the abundance of photosynthetic life, variations in erosion, saturation changes of carbon in sea water, how that affects minerals, and much more.Creationists need to acknowledge that we weren’t there during the “early earth” (however old one believes it is), and so we have similar issues understanding what δ13C means. Knowledgeable geochemists should first study the paper and determine its potential significance. For now, the take-home message should be caution about proxy measurements and interpretations of the unobservable past. What scientists confidently assert about earth history may rely on a “broken reed of a staff which will pierce the hand of any man who leans on it” (II Kings 18:21).
Mastering color correction means understanding the color channels that make a good image. Here’s how to isolate the chroma and luma channels in Premiere.I’ve covered noise reduction somewhat extensively over the past few months. In my article on manual noise reduction in Resolve, we took a look at the powerful results you can get from isolating the chroma and luma channels to apply noise reduction to each.Today, we’re going to learn how to isolate and work with image channels in Premiere — or any other similarly functional NLE. As with Resolve, there isn’t a plugin or button to quickly split your channels for you, so we’re going to do it manually.Before we start, what is the point of splitting the component channels?Each video clip is actually a blend of three distinct image channels. To put it simply, these component channels contain Luminance (or brightness and contrast) information, red color information, and blue color information. Baking these three channels into a single video stream enables much faster playback and simplicity of use.It is always good to know how to break down anything into its component parts, so without further ado, it’s time to split . . .Splitting Image ChannelsUnderexposed Donuts! The first step after you load your clip into a timeline is to duplicate the clip. In Premiere, the default quick keys for duplicating clips are alt+left click for windows and option+left click on mac.Separating LuminanceTo pull the chroma information out of our luma channel, all we need to do is navigate to the Basic Correction tab in the Lumetri color panel and slide the saturation to 0%.Separating Chroma ChannelsSeparating the chroma channels involves a few more steps. To start, duplicate your original (full-color) clip and place it above your luminance clip on the timeline. From here, navigate to the Curves tab in Lumetri and drag the top right point on all the curves (except for red) all the way to the bottom. Essentially, we’re cutting everything except for the red color in the shot.Duplicate the original clip once more, and place it on top of your red and luma clips. Now repeat the curves adjustments, but this time, isolate the blue channel.Now repeat the whole process once more for the green channel, placing it on top of everything.Technically, there isn’t a green color channel in the original clip, but I usually find the best results by including it. Test using or excluding it for your own clips.Now, go through each color layer and set its Opacity Blend mode to Lighten, but leave the opacity at 100%. (There are multiple blend modes and methods that will yield similar results, so experiment.)Your footage channels are now separated out by luminance and color, and you should finally have a normal-looking image again.Working with Split ChannelsNow, let’s look at a couple of things we can do to improve our donuts a little more.First, I’ll clean the timeline up a bit by nesting the three color channels. This is entirely optional, but I prefer previewing as few video layers as possible.One of the most useful reasons to separate luma from chroma is for sharpening your clip. Because the luma channel determines how we perceive sharpness, we can sharpen it individually from the color info, resulting in a clearer image without a lot of the nastiness that comes from sharpening footage in the color channels.But be careful not to go overboard — I’ve sharpened this clip by less than 20%.Cleaning up BlockinessOn the window to the left of the donut, we can see some severe artifacting caused by bringing the levels up on this shot. Let’s fix that.Select the chroma layer, and then head to the HSL/Secondary tab in Lumetri. Enable grey selection preview, and then find where the problematic blocking is by qualifying each channel.I’m fairly happy with my selection, so I’m just doing some basic tweaks to reduce its visibility.While we haven’t eliminated the blockiness entirely, we’ve pretty effectively covered it up. So let’s pull it out just a touch more.Chroma Channel Noise ReductionNow, we’ll apply Neat Video to the chroma layer and launch the plugin. I’ll do my best here to select this specific region of noise, despite Neat Video’s attempts to tell me that the region is too small. I usually shoot for 60% or greater selection quality, but here I was only able to get to about 45%, which should still work.Now move into the Noise Filter Settings to preview and tweak the results. With a bit of (uncharacteristic) luck, I think I’m good with the default filter settings. So, I’ll commit the changes and return to Premiere to ensure everything looks good there.I’ve tweaked the color on the results just a hair, and I think we’re looking great!Before.After.And that’s it! We have successfully split out our original footage into its component channels and brought the exposure to a much more appealing level while making the clip look even better than before.So try this method out if you’re having trouble salvaging your underexposed clips. There is so much more that you can do with your image channels separated — load up some clips, and see for yourself.Cover image via Simon Mayer.Looking for more articles on post-production? Check these out.Post-Production Tip: Quick and Dirty Noise Reduction Without a PluginHow to Get Better Color Grades Using Opacity Blend ModesImprove Your Masks with Hue, Saturation, and Luminance QualifiersPost-Production Tips: How to Save Corrupted FootageUnderstanding the Opacity Blend Modes in Adobe Premiere Pro