Why the earth oxygen level is depleting?

It isn't, the level of O2 on the Earth is relatively stable.  Minor fluctuations can cause a tiny change, but the level has remained about the same during the time humans have been monitoring it.

https://weather.com/science/nature/news/earth-atmo...

It is not depleting.  Anyone who tells you it is lying.

We keep destroying rainforests (the "lungs of the earth").  I'm sure the wildfires in CA, Australia, Siberia, and the Amazon burned up a lot of oxygen, too.

Is it?  I don't think so.  Oh, and you or your namesake is a traitor to the nation and ought to have been put in jail for acts counter to the interests of the USA while acting as VP for the country.  I haven't forgotten.

It's not, in any ongoing way. It may vary fractionally with climate variations, but by trivial levels.

Carbon dioxide is consumed by plants, trees etc. and most importantly marine algae, which retain the cardon and release oxygen.

More CO2 in the atmosphere means more "free food" for such things, causing algae blooms and giving other forms of sea life more food.

It is not really that it is depleting. But because it is more and more in the form of CO₂

O₂ is part of a cycle, a balanced one, with CO₂. Plants capture CO₂, to build their own biomass using C, and reject O₂. Then plants are burned. Either by fire, or because they are eaten by animals who "burn" it. Both case, the result is the same: combustion reaction take back C in the plan, and combine it with a O₂ taken from the atmosphere, to create CO₂ again.

Growth of plant is compensated by their burning, because an equilibrium has been reached between the 2 process. Nothing magical: if there were too many plant, then, there would be less CO₂ for them to thrive on, more O₂ in the atmosphere to ease animal live, and fire, so in the end, less of them. If there were too few plant, there would be more CO₂ in the atmosphere to have them thrive, and less O₂ to have them burn. So, in the end, more of them.

So there has to be an equilibrium after a while.

Once upon a time, billions years ago, there was far more CO₂. And no animal life. The equilibrium was almost without O₂. And that equilibrium, without any animal life possible, seemed to be for ever. But, from times to times, somewhere on the planet, accidents occur. A tree get trapped in lava for example. So it doesn't burn completely. And the carbon it contains does not return to the atmosphere. This is what is called fossilization.

And when it occurs, a very small quantity of carbon is removed from the carbon cycle between plants and atmosphere. So, less CO₂, more O₂.

It is completely negligible. Except that, after a few billions of years of those infinitesimal removal, there was enough O₂ in the atmosphere so that animal life could exist. And here we are.

Now, for one century, we have been reversing very fast that process. By finding those fossilized organism (turned into oil, gas and coal since then) and burn them.

So, obviously, we are going back, quickly, to the initial equilibrium. The one in which there was no possible animal life. More CO₂, less O₂.

And people won't even believe that until they wake up one morning and they discover they can't breathe we're having far and far less trees and grass each and every day without grass and trees what is there to make the air that you breathe