# Tag Info

36

what evidence do we have that the asteroids indeed formed at the same time as earth? It depends on what is your definition as "the same time". The formation of the solar system and Earth did not happen at a particular second in time but was rather a continuous process. It also depends on what you define as "asteroids". I'll try to put some things in order. ...

25

Yes, the age of the Earth is about 4.5 billion years (4,500 million years). Your linked articles describes well how it was formed and how we know about it. The uncertainty is less than 1% and depends partly on the radiometric dating methods and partly on the definitions. Sometimes the age is said to be 4.567 Ga, that might be a little too exact number to ...

12

The formation of a T-Tauri star spells the beginning of the end of the protoplanetary disk from which planets and asteroids can form. The end is nigh when that star ignites. The large solar winds and solar radiation pressure sweep the disk clean of all small objects. Some spirals inward, some outward. There's no dust and no gas from which new planets and ...

12

There is a technique called "Exposure Dating". Using e.g. cosmogenic nuclides (they are produced in the first metre or so of the surface of a rock which is exposed to cosmic rays, i.e. on the surface of the earth), it is possible to estimate the amount of time that the rock was exposed. With some assumptions, you can get an exposure age of the fracture ...

12

Organic material (plants and animals) contains carbon. Carbon has three main isotopes: carbon 12, 13 and 14. Carbon 14 is radioactive, with a half life of 5730 years. Carbon 14 is continuously created in the atmosphere by cosmic rays hitting nitrogen. The nitrogen atoms lose a proton when struck by cosmic rays, turning the affected nitrogen atom into an ...

11

Yes, there is some amount of circular reasoning in the statement: "geologist date rocks by the fossils they contain and date fossils by the rocks in which they are found". However, that statement does not fully describe how geologists date rocks or fossils. Dating rocks by fossils is a branch of geology called "biostratigraphy". This is a non-absolute and a ...

11

The estimates of Newton and Kepler, and the similar estimates of dozens of their contemporaries, were produced by treating the Bible as a historically accurate document and deriving a chronology from it. I think that a detailed explanation of their techniques would be off-topic for Earth Science, but the Wikipedia page on the Ussher Chronology (which ...

10

Not as far as I am aware. Any dating of the rock would determine the formation age of the rock (dating isn't quite as straight forward as that, and there is a whole science behind what each dating technique actually determines but for simplicity's sake we say it is the formation date) but the fracture plane,where the hand sample has broken away from the ...

10

I think this is very hard to answer this question as it is exactly this ambiguity that caused the International Commission on Stratigraphy to discard the names Tertiary and Quaternary for there are no clear limits to these era's. For example, the name Quaternary was only introduced some 70 years after the name Tertiary (source), and Neogene covered both the ...

7

I can't be entirely sure but I'll make an informed guess: That value doesn't come for a single measurement. Therefore, if the error in the age of a single sample is $\pm125$ kyr, you just need to average 16 samples to get it down to $\pm31$ kyr. The uncertainty in the addition (or substraction) of two or more quantities is equal to the square root of the ...

7

In addition to what @Michael said, one can add that the claim that "geologist date rocks by the fossils they contain and date fossils by the rocks in which they are found" is misleading: are some rocks being dated using fossils? Yes. Are some fossils being dated by the rock they are contained in? Yes. But they are not the same fossils or the same rocks in ...

7

I'd like to add a bit to the existing answer and maybe break it down to several simple things: Chloride likes water. The chloride ion, Cl- really likes being in water. It's one of the most incompatible elements in mantle melts, and it readily partitions into fluids exsolved from magmas. Basically, it's enriched in silicic rocks (that are forming most of the ...

7

Biostratigraphy - observing which fossils were present in which stratigraphic units, and using minimally-deformed sequences to determine age order - gives us relative ages of fossils. Absolute ages, however, rely on geochemical chronometers: just like dating the reversals in the Earth's magnetic polarity by establishing how old the oceanic crust that ...

6

Typically this is accomplished through radiometric dating. While this is a complex field and the article I've provided a link for explains it better than I could here, the short answer is that different elements' isotopes decay to at a known rate, and by measuring the quantities of the isotopes in question (which are chosen depending on the approximately ...

6

I will try to plainly answer your question about an artificial radionuclide production/diffusion resulting from human activities, without getting into the discussion of deciding if this is geochronologically relevant or not. I would point Figure 1 of this paper which indicate the average tritium (3H) levels in the northern hemisphere between 1945 and 2008. ...

6

Certain anthropogenic radionuclides have pragmatic advantages as markers for the start of the anthropocene. The advantage of radionuclides over anthropogenic stable nuclides is that the primordial production of all but a few radionuclides has decayed away. Thus natural background levels are below detection by sensitive analytical methods except in a few ...

5

The chapter on the Anthropocene (Zalasiewicz et al., 2012) of "The Geological Timescale 2012" quote 3 papers that used artificial radionucleotides as stratigraphic markers: Schwikowski (2004), Turetsky et al. (2004) and Marshall et al. (2007). The first one (Schwikowski, 2004) used them in the context of dating ice cores from Alpine glaciers and the second ...

4

The age of 4.55Ga for the Earth is actually a date of "hard stuff" based on Iron-Nickel meteorites, dated using radio-isotope dating. If you had enough meteorite samples it should be possible to identify those with isotopes that imply a different age. For example, when plotted, their Pb isotope ratios will have different gradients. We do not see this.

3

It sounds like there are two primary ones: No, these are not the two "primary ones". The method used depends on what you are dating, and what age you expect it to be. Radiocarbon dating is relevant to things younger than a few tens of thousands of years, and it's only relevant for things that were living (or growing), and incorporated atmospheric carbon. ...

3

Here is a graph describing modern estimates of ocean salinity throughout the Phanerozoic (past ~550 million years). The original PDF of this study can be found here: Hay, W.W., Migdisov, A., Balukhovsky, A.N., Wold, C.N., Flögel, S. and Söding, E., 2006. Evaporites and the salinity of the ocean during the Phanerozoic: Implications for climate, ocean ...

3

The fact that the overwhelming majority of celestial objects within our solar system orbit in a like manner (same direction as the Sun's rotation) is observational evidence that they formed at about the same time from the same processes. A rogue planet/proto-planet/asteroid captured by our solar system's gravitational footprint in space time would have a 50/...

2

What exactly are you trying to measure? some of the great North American and Andean batholiths have cooling histories of at least 20 million years, and maybe more than 50 million years. It is perhaps inappropriate to think of the crystallization process as having a single date. Phenocrysts near the top of the pluton are cooler, but may sink to deeper levels ...

2

Yes it is used and it works. I've heard varying viewpoints on it's accuracy and dependability though. I remember my earth science lecturers were in three camps with it: one felt that the dates weren't consistently reliable, the data he'd gotten from astro-dating in the past had very poor independent confidence margins when there was no radiometric ...

2

My thought is that you would not see any correlation because grain roundness has to do with how long it has been in the sedimentary system rather than its crystallisation age. That is, if one sampled a modern sediment in which a 650 Ma zircon grain from a 650 Ma granite has only recently been eroded from its granite source then one would expect this zircon ...

2

Your question may be better suited to either SE History or SE History of Science and Mathematics. The date of the so called creation of the Earth has nothing to do with Earth Science. For Kepler I found he wrote the book KANONES PUERILES, in it he calculates the creation date to be 27 April 4997 BC. The published works of Newton reveal little. Some authors ...

1

There are huge datasets of geochronology available in the published literature. Unfortunately there is not one single database because the task is daunting (there are several thousand geochronology labs in the world which typically produce hundreds of ages per year). Some papers discussing how data should be (and often are) reported are these, for example : ...

1

The better site for sample collection would be the accessible site where it's possible to pick up a sample. Unless you have a drill rig or an excavator, you are limited to what's exposed. If you still have access to several zones of the pluton, take all of them. The more samples you have, the better it is. By choosing not to sample a certain zone you might ...

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