# Why limestone formation was not a concern in atmosphere oxidation event? [closed]

I have just got to know why Fe was a problem. After clay (alumnum) and Silicon got oxidized, there has left a lot of unoxidized Fe in the crust, whose oxidization has finished during GOE. But, ferrum was not the only consumer of the oxygen.

If I look at the upper layer of the soil

you will see a lot of CaCO3 (aka limestone or calcite) and oxidized aluminum Al2O3 (aka the clay) with sand below it. Nowhere you will see the (oxidized) Ferrum in noticeable amounts. How could Fe be the major consumer of the oxygen despite calcite is present in much larger amounts?

• I can't make much sense of this question. You seem to be asking about the Great Oxygenation Event (~2.3 Ga), but you're presenting a stratigraphic column of the Baltic Klint, which is nearly 2 Gyr younger. There are many false premises here: the Paleozoic Baltic Klint is not "the upper layer of the soil"; aluminium is not clay; aluminium oxide is not clay; the column contains sandstone, not sand; and the clay is below the sandstone, not above it; and you claim there's no oxidized iron despite the thick glauconitic layer in the column. – Pont Jul 29 '16 at 15:48
• @Pont The layer is younger, it is basically made of oxides. A terrible amount of oxides appeared after the GOE but their formation did not delay the atmosphere oxidisation the way free Fe did. It makes no sense indeed. – Little Alien Jul 29 '16 at 16:06
• Those metals were already oxidized long before they were deposited. As Michael explained to you, this happened rather early in the Earth's history. There were no lumps of elemental calcium in the Paleozoic oceans waiting to be turned into limestone -- if you watch this video showing the effects of dropping calcium into water, you'll understand that this would have been an unlikely scenario! :) – Pont Jul 29 '16 at 17:47
• @Pont How can you say that mine question was answered there? I do hot hear the statement of the chemical reaction in your video. I can only guess what is happening and do not see any reason for that after after Michel has everything explained. – Little Alien Jul 29 '16 at 22:23
• I have checked the chemistry. Calcium + water gives me hydroxide. It will exchange CO2 for H2O to from the limestone. This suggests that we still consume Oxygen from the atmosphere. Which pre-oxidization are you talking about? Have you read the Michael's answer to direct me to read it again? – Little Alien Jul 30 '16 at 0:52

First, let me clarify this again:

Al2O3 is not clay.

Now, back to topic. You are mixing apples and oranges here. The geological section you are referring it was deposited 2 billion years after the GOE. This was long after all surface iron was oxidised, and abundant oxygen was present in Earth's atmosphere.

Nowhere you will see the (oxidized) Ferrum in noticeable amounts

Iron is not present in this geological section, but it is present elsewhere. You are looking at one specific section in one specific locality on Earth's surface. It is flawed logic to infer what you are based on this.

How could Fe be the major consumer of the oxygen despite calcite is present in much larger amounts?

Because at this stage, neither calcium nor iron were "consumers" of oxygen. Oxygen has been consumed before, and then this consumption stopped once all of the iron was oxidised. This is why oxygen today exists in the Earth's atmosphere.

@Pont The layer is younger, it is basically made of oxides. A terrible amount of oxides appeared after the GOE but their formation did not delay the atmosphere oxidisation the way free Fe did.

I have checked the chemistry. Calcium + water gives me hydroxide. It will exchange CO2 for H2O to from the limestone. This suggests that we still consume Oxygen from the atmosphere. Which pre-oxidization are you talking about?

Metallic calcium probably never existed in the Earth at all. The GOE was a process in which only iron was oxidised (out of the major components of the Earth's crust). The oxidation of calcium, aluminium, silicon, etc, occurred much before that. It occurred when the Earth was forming, and possibly even in the solar nebula that existed before Earth even formed. This was 2 billion years before the GOE.

Let's put this on a time line:

1. ~4.5 billion years ago, Earth formed. Calcium, aluminium, silicon were all oxidised. Only some of the iron was oxidised.
2. ~2.5 billion years ago. Photosynthesis causes oxygen to rise, but the rise is limited because of the presence of iron in the crust. Any oxygen that is produced, is consumed by the oxidation of iron. Eventually all iron is oxidised and oxygen contents can freely rise.
3. ~0.5 billion years ago. The section you refer to is deposited.
• Thanks. To dot and cross the iis, here is a piece of Wikipedia: The quicklime, CaO, is not stable and, when cooled, will spontaneously react with CO2, which explains why we did not need the single O for Ca during the oxidation event after your answer. – Little Alien Jul 30 '16 at 6:47
• @LittleAlien when geoscientists talk about simple oxides (Such as CaO, Al2O3, etc), usually we do not mean the actual compound. We usually refer to the chemical component in another compound (for example CaO in calcite or Al2O3 in clays). When we do actually mean the chemical compound, we usually call it by its mineral name (e.g. quartz or corundum), instead of the chemical component. – Gimelist Jul 30 '16 at 6:50
• +1, great answer which does a good job of clarifying the question as well as answering it. My only nitpick is that iron does happen to be present in this section (as glauconite and Fe-ooids), though of course this doesn't make any difference to your explanation. – Pont Jul 30 '16 at 9:58