Thread: Sunlight and Earth's Primordial atmosphere

Earth's atmosphere was created by volcanic activity, true?

If so, was the atmosphere cloudy and obscured?

How much sunlight penetrated the atmosphere?

Was the sun visible from Earth's surface?

If not, when did the atmosphere clear up enough for the sun to be visible?

Most think it was a volcanic mix Co2, water vapor, nitrogen etc.
Some recent work has added a significant amount of hydrogen as well.
Most of what makes volcanic eruptions so opaque is solid aerosols, most of which either quickly settles out or scrubbed out by rainfall. Of course that doesn't mean is was clear. Many think the atmosphere could have has held an organic haze much like Titan. We're pretty sure that the sun was something like 30% dimmer which has given scientist difficulties modeling temperatures high enough to keep liquid water on the early earth's surface though a recent study suggest higher air density could have added enough green house effect to have made the difference.

Do we know if the sun itself was visible? Or was it like an overcast day where the Earth is lit by the sun, but we cannot see the sun itself through the clouds?

oops, I hit New Thread instead of Add Reply.

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After a supervolcano eruption, upwards of 90% of solar radiation is blocked out by the resulting airborn ash and oxides of sulphur. If we can assume that during the hadean, there was much prolonged and more severe volcanism worldwide, it may be that 95% or more of solar radiation was blocked out by the atmosphere for the first 300 million years of the Earth's history or so. During this time it is widely accepted that cellular life did not exist on the Earth.

Originally Posted by Socratic Spelunker

oops, I hit New Thread instead of Add Reply.

Can a mod please merge this with the other thread of the same name?

Thank you.

done - pls continue

Originally Posted by drowsy turtle

After a supervolcano eruption, upwards of 90% of solar radiation is blocked out by the resulting airborn ash and oxides of sulphur. If we can assume that during the hadean, there was much prolonged and more severe volcanism worldwide, it may be that 95% or more of solar radiation was blocked out by the atmosphere for the first 300 million years of the Earth's history or so. During this time it is widely accepted that cellular life did not exist on the Earth.

Interesting, so at what rate did it clear up and become "an organic haze much like Titan?"

Originally Posted by Socratic Spelunker

Originally Posted by drowsy turtle

After a supervolcano eruption, upwards of 90% of solar radiation is blocked out by the resulting airborn ash and oxides of sulphur. If we can assume that during the hadean, there was much prolonged and more severe volcanism worldwide, it may be that 95% or more of solar radiation was blocked out by the atmosphere for the first 300 million years of the Earth's history or so. During this time it is widely accepted that cellular life did not exist on the Earth.

Interesting, so at what rate did it clear up and become "an organic haze much like Titan?"

Good question. Assuming the volcanic activity stopped instantaneously, the atmosphere might clear over a few hundred or thousand years; alternatively, these conditions may have persisted for millions of years. It's not possible to say, because there are practically no rocks preserved from this time.

Curiouser and curiouser. So we don't know how long it lasted? Is there even any commonly accepted estimate? Is it at least safe to assume that it was before the beginning of photosynthesis? Maybe not, since some plants thrive just fine in dim conditions...

I see where you want to go. Linking this to photosynthesis is hasardous. The first life has been assumed to be RNA based. Which means there was no real well defined shapes or species as the RNA is extremely mutable.

Then, came the DNA based life, more stable, but still using RNA as intermediate system to self replication, a 'chemical fossile' of former life species. This first DNA life form might have survived on chemiosynthesis or, like a recent theory, could be even related to these deep buried nanobacterias.
Photosynthesis might be simply a evolution mechanism of defense as oxygen is toxic for most other bacterias. A bit like the chemical released under walnut trees or pinetrees. It means there was probably already an ecosystem of bacterias when photosynthesis appears. We are talking 100s of millions of years after the first life appearance, so the atmosphere was clear.

ok, so just to be clear...

Photosynthesis started about 1.1 billion years after earths initial formation, right? We're saying that the atmosphere was cleared up by then, yes?

I am not a biologist, just a stupid geologist. But my 2 cents advices for you to find a beginning of solution:
1/ If the atmosphere was clear, we can assume the light of the sun was similar to now or if not, we can reconstruct the spectrum of the light of the sun.
2/ There are 5 or 6 types of chlorophyle pigment. They are fund on the different species. We could assumed that the older species (cyanobacteria/stromatolithe) are hosting the most, less mutated type of chlorophyl. This is chlorophyl e and chlorophyl f.
3/ By studying the spectrum of absorption of these e and f and comparing the shift of the more recent chlorophyl, we will see already interesting information.
4/ By comparing this shift to the one between the present and the former light of the sun, we will get other interesting information. I can almost bet it is similar but amplified.
5/ If it is not, I guess you found something about the atmosphere. It is the only parameter left in our analysis.

Good luck...

Originally Posted by Socratic Spelunker

ok, so just to be clear...

Photosynthesis started about 1.1 billion years after earths initial formation, right? We're saying that the atmosphere was cleared up by then, yes?

Yes, the sulphur oxides and ash from the hadean volcanic period would have been cleared from the atmosphere by this time. It probably didn't take too long once the volcanism died down; the proto-atmosphere had a high concentration of water vapour, which would have condensed to form clouds by nucleating around ash/sulphur particles, thereby removing them from the atmosphere in rain. Some sulphur and ash may have persisted in the stratosphere and mesosphere for longer - say a few tens of thousands of years - but after a billion years the atmosphere would certainly have allowed sufficient light through to allow for photosynthesis.

what caused the high concentration of water vapor? How long did that last?

Even today water vapor is most common gas released by volcanoes.

Originally Posted by Socratic Spelunker

what caused the high concentration of water vapor? How long did that last?

The Earth was much hotter back then, so water at the surface evaporated in greater quantities - as well as water vapour released from volcanoes. The concentration of water vapour in the atmosphere depends largely on the temperature of the atmosphere, and the rate at which it is input by volcanic activity, so as the Earth cooled and volcanic activity decreased, the water content of the atmosphere would have decreased too. Water vapour tends not to hang around in the atmosphere for too long; a large amount has just been deposited as snow where I live.

80 percent of the Earth's atmosphere was outgassed from the mantle during the Earth's first one million years! The rest was released slowly but constantly during the next 4.5 billion years.

Quite suprising really!

About 4.3 Ga, water made up 25% of the atmosphere, then dropped to near todays levels within 500 million years!