# Tag Info

38

Some background: We are able to determine the age of certain rocks and minerals using measurements of radioactive and radiogenic isotopes of certain elements. The most common are U-Th-Pb, Rb-Sr and Sm-Nd. Simply put, the resulting date is the time that has passed from the crystallisation of that mineral. Obviously there are complexities, but there are not ...

19

The answers that have been provided are correct but they're omitting the fundamental issue that explains why they are correct: When you date a rock you get the point that it solidified, not the point the material came into being. Most rocks on Earth have melted time and again and thus are useless for figuring out how old the Earth is.

10

A few elements to complement @Siv answer, and some alternatives hypotheses: Originally the idea was that the Fe2+ oxidation into Fe3+ that lead to the formation of the BIF ("banded iron formations") was an indirect consequence of the increased atmospheric pO2 caused by the photosynthetic activity of, then freshly appeared, cyanobacteria (see e. g. Cloud ...

8

The answer might lie in aerobic respiration. This is of course only one of the many possible explanations but mitochondria (and therefore $\ce{O2}$-breathing eukaryotes) are thought to have evolved circa 2.3 to 1.8 Ga (see for instance Hedges et al., 2001; 2004; 2006). This loose age bracket however is based primarily on molecular data with very few fossil ...

8

There is no evidence that Earth had a much greater axial tilt so long ago. To my knowledge, the evidence for changes in the axial tilt of the Earth is based on ocean sediment cores (see http://en.wikipedia.org/wiki/James_Hays ) and ice cores ( see http://en.wikipedia.org/wiki/Milankovitch_cycles#Axial_tilt_.28obliquity.29 ). However, these only go back ...

7

There's a little more to it than its substantial age, but not a lot. First, a bit of background. We need a few conditions for accumulations of oil or gas: A kerogen-rich source rock that has been 'cooked' to thermal maturity. Insufficient temperature, or insufficient time, and it's undercooked; if the temperature is too high, or the rock is very old, then ...

6

Simple enough, see the meteorites formed alongside the planet, however, since the planet was pretty much a molten soup you can't date it properly, because we can only date it after it cooled down. Meaning that the meteorites hold a much more accurate time-frame since they were not melted down to form our crust! which means their dates (I am using the term ...

6

At μ/g level some decade ago, they were explained as forming in relation to the oxygenation of the atmosphere, as photosynthetic life developed changing a reducing environment to an oxygenated one, iron oxides formed precipitating out of seawater in variable bands related to local (or possibly seasonal) oxygen availability. Though this traditional ...

3

It is and is not an an error depending on how it is used. They are Eons but in older literature they were also, sort of, eras as the Eons were not subdivided as they are now. Especially in literature dealing with the transitions they might refer to them indirectly as eras, such as "In the previous Proterozoic era", proterozoic being possessive. At the time ...

3

I don't totally understand what you are asking but yes there was soil in the Archean. In some locations around the world, these soils were buried and preserved as paleosols. The Archean paleosols are very important in studying the origin of the atmosphere because the oxidation state of the minerals is an indicator of the presence or absence oxygen and other ...

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