How do we tell the difference between geologic ages?

Jan 3, 2020
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Earth's history is long. How do scientists keep track of what happened when?

How do we tell the difference between geologic ages? : Read more
Integrated genomic and fossil evidence agree that life evolved way before the first 10 % of Earth's history ended, likely right after the global ocean reformed after the Moon forming impact [ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6152910/pdf/emss-78644.pdf ].

Which brings me to the suggestion, not yet accepted by IGUS, to define convenient pre-Hadean solar system geological ages [ https://en.wikipedia.org/wiki/Hadean#Subdivisions ]. The common Chaotian Eon of the planetary disk dust and rock assembly would split into separate planetary geology. For Earth Chaotian would end then the proto-Earth body, labeled Tellus, would be hit by the Theia impactor to gain its last 10 % of mass and a big Moon [ https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100036717_2010036774.pdf ].
 
Mar 8, 2020
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Science has given way too much energetic credence to the idea of an asteroid impact destroying the dinosaur epoc... an asteroid could not have possibly done as much damage as is reported...if one did possibly hit in the yucatan area as storied..the area looks more like a senote ut an impact crater...we must not ignore the iridium left behind...from the use of expended atomic weapons...yes they are an old device..past great technologies used to inhabit this planet and war among them selves sadly enough..and doing great damage to this diamond in the vast galactic sea of space..we best at using common sense when looking at big events..so the science and political establishment does not get to let to us any more.
 
Feb 19, 2020
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The first 10% of Earth's history is supposed to be anoxic. The biggest difficulty with the GOE and the anoxic atmosphere-ocean hypothesis is the simple fact that cyanobacteria cannot live and grow (even survive) in an ocean saturated with reduced iron. There have been no successful experiments simulating such conditions. This alone falsifies the GOE and any phylogenetic theories about the LUCA that rely on that.
 
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Dec 11, 2019
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The change was spurred by the asteroid impact that eventually killed the nonavian dinosaurs. -- from the story

I'm sorry but, again, calling birds 'dinosaurs' angers the heck out of me. Birds are NOT dinosaurs in any real sense of the word. Birds evolved FROM dinosaurs and so belong to the same biological clade. But then, mammals evolved from therapsids and belong to that clade but we don't go around calling mammals "therapsids". Calling birds dinosaurs started as a kind of paleontological joke/fad a couple of decades ago when the clade system became widely used because some paleontogist(s) likely thought it was cute and clever. So of course, science journalists took up the fad. But it is misleading and bad biology (as well as bad science journalism).
 
Feb 19, 2020
136
27
130
The change was spurred by the asteroid impact that eventually killed the nonavian dinosaurs. -- from the story

I'm sorry but, again, calling birds 'dinosaurs' angers the heck out of me. Birds are NOT dinosaurs in any real sense of the word. Birds evolved FROM dinosaurs and so belong to the same biological clade. But then, mammals evolved from therapsids and belong to that clade but we don't go around calling mammals "therapsids". Calling birds dinosaurs started as a kind of paleontological joke/fad a couple of decades ago when the clade system became widely used because some paleontogist(s) likely thought it was cute and clever. So of course, science journalists took up the fad. But it is misleading and bad biology (as well as bad science journalism).
This is just a semantic argument. Misleading but irrelevant to telling the difference between one geological event and another.
 
Mar 10, 2020
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Earth's history is long. How do scientists keep track of what happened when?

How do we tell the difference between geologic ages? : Read more
The oldest method was to note the different stratigraphic layers, e.g. alternating sandstone, limestone, volcanic and plutonic layers. The change in layers represents a change in geological processes. These changes may occur on a regional or global scale. Internal fossils, if any, constrain the age and allow one to tie different regions together. Stable radiometric minerals, if any, allow radiometric dating and correlations across regions.

Early geologists in Britain, France and Germany developed the method of stratigraphic dating in the 1700s. Radiometric dating was not developed until the 1900s.

Field geologists, when geologically mapping a new area, create a reference stratigraphic column for that region. It may be substantially the same as nearby geologic regions, but with local deviations. In some cases the column might be considerably different from nearby columns due to crossing a plate tectonic boundary where there were large horizontal motions between the plates over the geologic ages.
 
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Jan 3, 2020
152
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Science has given way too much energetic credence to the idea of an asteroid impact destroying the dinosaur epoc... an asteroid could not have possibly done as much damage as is reported...if one did possibly hit in the yucatan area as storied.
The impact is a well tested observation. with the geological residues (iridium, shocked quartz, cenote ring, seafloor ring, strewn field) and the latest drill results (show the event sequence). The effects would suffice according to many papers.

The debate was not that there was am immediate change to a new geological era and that it was caused by an impact (iridium boundary layer), it was if the impact was alone. That was recently shown to be the case by finding well preserved sediments so giving finely resolved dating. The other factors made their stuff at the wrong dating (some 0.2 Myrs separation, IIRC).
 
Jan 3, 2020
152
11
605
The first 10% of Earth's history is supposed to be anoxic. The biggest difficulty with the GOE and the anoxic atmosphere-ocean hypothesis is the simple fact that cyanobacteria cannot live and grow (even survive) in an ocean saturated with reduced iron. There have been no successful experiments simulating such conditions. This alone falsifies the GOE and any phylogenetic theories about the LUCA that rely on that.
Earth was observably anoxic for 50 % of its age, based on observation. A recent isotopic analysis show that oxygenation can have been coeval with the ending of high mantle/crust heat flow with thin, sluggish plate tectonics and starting the growth of continents [ https://www.nature.com/articles/s41561-020-0538-9 ]. Anoxic Earth, since "[h]igh-temperature fluid–rock interactions strip 16O from hydrother-mal fluids, ...".

The cyanobacteria ancestor lineage is very old, and it was and is poisoned by oxygen as everything else so the GOE meant it too saw 99 % species extinction. Its modern fair oxygen tolerance (though RuBisCO that can't separate much between O2 and its target CO 2is a bummer) evolved.

"Integrated genomic and fossil evidence illuminates life’s early evolution and eukaryote origins", https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6152910/pdf/emss-78644.pdf; but see the image from https://phys.org/news/2018-08-timescale-evolution-life-earth.html !!! For some reason the mounted image gets kicked out from LifeScience server, so you have to go to the link. It shows the dating for cyanobacteria, GOE and chloroplasts in a cleaner manner than the original paper.

The above phylogeny show that nothing is falsified by the geology but instead supports the evolutionary tree (since, well, evolution). By the way, and as a reflection on the article description of life and geology coevolving, the integrated evidence credibility range for evolution of LUCA is ~50 Myrs right after the Moon forming impact. It's coevolution all the way down.
 
Jan 3, 2020
152
11
605
I'm sorry but, again, calling birds 'dinosaurs' angers the heck out of me. Birds are NOT dinosaurs in any real sense of the word. Birds evolved FROM dinosaurs and so belong to the same biological clade. But then, mammals evolved from therapsids and belong to that clade but we don't go around calling mammals "therapsids". Calling birds dinosaurs started as a kind of paleontological joke/fad a couple of decades ago when the clade system became widely used because some paleontogist(s) likely thought it was cute and clever. So of course, science journalists took up the fad. But it is misleading and bad biology (as well as bad science journalism).
I believe the terminology has been adopted in most papers. You can't get a consistent terminology mapping between taxonomy, morphological/fossil species and genomic biological species - and it's even worse for prokaryote OTU clustering. What we can do is to make useful taxonomy. Birds as dinosaurs, mammals as archosaurs, ..., tetrapods as fishes et cetera is useful if you want to illustrate evolutionary relationships and avoid confusing paraphyly.
 

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