% change in atmosphere on a lifeless Earth

[wd40]

If all life suddenly ended on Earth, flora and fauna, including plankton, bacteria and viruses, would there be any significant change in the % of Nitrogen, Oxygen and CO2 after 100, 1000 and 1 million years?

[eburacum45]

After 1 year, probably no significant change.

After 100 years the oxygen level would dip, and the CO2 level would rise, as the dead organisms in the biosphere oxidised.

After 1000 years the biosphere would be significantly oxidised, and fires in the dead forests would have eliminated much of the (former) biomass; the CO2 level would have gone up a lot and the oxygen level would have come down by maybe a percent or two. Exactly how much depends on the mass of the current biosphere versus the mass of CO2 and oxygen in the current atmosphere; if anyone has detailed estimates of these figures we might be able to find out just how much the atmosphere would change. I would guess that even after 1000 years the atmosphere would still be breathable.

After a million years most of the free oxygen would have been absorbed by the Earth's crust, so we would be left with nitrogen and CO2. The level of nitrogen would not change significantly, as far as I am aware.

[eburacum45]

Now I come to think of it, forest fires might have a significant effect on CO2 levels within a few years. I don't know what would happen to the dead phytoplankton in the sea, though; probably it would sink and be buried, therefore might not make much impact on the atmosphere. In the absence of decay organisms, it wouldn't rot.

[cran]

If you assume ongoing tectonic activity, then at the 1000 and 1 million year intervals, you would notice little and no free atmospheric oxygen respectively because volcanic gases will oxidise if it can. Without something to produce free oxygen, carbon dioxide and sulfur-based gases will tend to accumulate. Eventually, you would be looking at something like Venus.

[Inclusa]

If you assume ongoing tectonic activity, then at the 1000 and 1 million year intervals, you would notice little and no free atmospheric oxygen respectively because volcanic gases will oxidise if it can. Without something to produce free oxygen, carbon dioxide and sulfur-based gases will tend to accumulate. Eventually, you would be looking at something like Venus.

I don't know if the OP assumes the possibility of re-emergence of biosphere.

[cjl]

If you assume ongoing tectonic activity, then at the 1000 and 1 million year intervals, you would notice little and no free atmospheric oxygen respectively because volcanic gases will oxidise if it can. Without something to produce free oxygen, carbon dioxide and sulfur-based gases will tend to accumulate. Eventually, you would be looking at something like Venus.

I'd be very surprised if you ended up with the atmospheric density of venus. I'd bet that the atmospheric density would stay more like what it is now, but with the oxygen content dropping and carbon dioxide and sulfur-based gases in higher concentration than today. I would think that nitrogen would remain as the dominant gas.

[wd40]

If humanity alone was suddenly made totally extinct on Earth, would one expect a detectable change in the CO2 % after 50 years?

[KABOOM]

If humanity alone was suddenly made totally extinct on Earth, would one expect a detectable change in the CO2 % after 50 years?

I would venture a guess of no material change. Displacement will occur. The numbers of other oxygeniating species will increase. The void will be filled.

[eburacum45]

If you assume ongoing tectonic activity, then at the 1000 and 1 million year intervals, you would notice little and no free atmospheric oxygen respectively because volcanic gases will oxidise if it can.

I agree with the second part of your statement, but not necessarily the first. The mass of oxygen in the atmosphere is 1.1776 x 10E18 kg. How much volcanic gas is expelled each year, and how many kg will be absorbed over 1000 years? Another oxygen sink is newly exposed rock in volcanoes and at spreading sites- but this quantity also needs to be assessed before we can estimate the oxygen level at the 1000 year mark.

[MikeMcc]

I assuming that we discussing the end of human caused CO₂ emission? In which case we are still looking at another an inital continuing rise in CO₂ together with a further rise in temperature. This would continue over the next 20-50 years until the earth reaches an balance point (ignoring any other driving forces that may have an influence). After that point the CO₂ level should decrease back to pre-industrial levels over the course of the next thousand years or so.

If we are assuming the bodies are still around then we have decomposition by-products to complicate the situation. If all plant-life is killed off then we have a drop-off in O₂ levels too.

[eburacum45]

The original post specifies that all life suddenly ends; this is a thought experiment of course. Since all life, including all photosynthetic life, is extinguished there is no reason for CO2 to decrease back to pre-industrial levels.

[cran]

I'd be very surprised if you ended up with the atmospheric density of venus. I'd bet that the atmospheric density would stay more like what it is now, but with the oxygen content dropping and carbon dioxide and sulfur-based gases in higher concentration than today. I would think that nitrogen would remain as the dominant gas.

Have you allowed for the water vapour content?

[cran]

I agree with the second part of your statement, but not necessarily the first. The mass of oxygen in the atmosphere is 1.1776 x 10E18 kg.

Is that before or after the other oxygen sinks as already mentioned are factored in?

Another oxygen sink is newly exposed rock in volcanoes and at spreading sites- but this quantity also needs to be assessed before we can estimate the oxygen level at the 1000 year mark...
(earlier)
After 1000 years the biosphere would be significantly oxidised, and fires in the dead forests would have eliminated much of the (former) biomass; the CO2 level would have gone up a lot and the oxygen level would have come down by maybe a percent or two. Exactly how much depends on the mass of the current biosphere versus the mass of CO2 and oxygen in the current atmosphere; if anyone has detailed estimates of these figures we might be able to find out just how much the atmosphere would change. I would guess that even after 1000 years the atmosphere would still be breathable.

With available cations, what happens to high concentrations of CO2 and O2?

How much volcanic gas is expelled each year, and how many kg will be absorbed over 1000 years?

I'll leave the calculations as an exercise for the student, but some of this might help for numbers:

There are about 1,000 mud volcanoes on land and 5,500 offshore — mostly in deep water. Activity varies between gentle emissions and violent eruptions accompanied by the release of enormous volumes of gas — mainly (85%+) methane and carbon dioxide. Global gas emissions are provisionally estimated to exceed 27 billion cubic metres per year, of which more than 23 billion (15.8 Tg) is methane. More than 70% of this is from short-lived eruptions, about 30% of which ignite to produce flames tens or hundreds of metres high. The majority of the methane is emitted by submarine mud volcanoes, most in deep water. About 11.4 Tg per year is lost to the hydrosphere, but a tentatively estimated 3.6 Tg per year escapes to the atmosphere.

Alan Judd, 2005; Gas Emissions from Mud Volcanoes
Significance to Global Climate Change

Mud Volcanoes, Geodynamics and Seismicity
NATO Science Series, 2005, Volume 51, Chapter 4, 147-157

...............

The most abundant gas typically released into the atmosphere from volcanic systems is water vapor (H2O), followed by carbon dioxide (CO2) and sulfur dioxide (SO2). Volcanoes also release smaller amounts of others gases, including hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCL), hydrogen fluoride (HF), and helium (He)...

Emission rates of SO2 from an active volcano range from <20 tonnes/day to >10 million tonnes/day according to the style of volcanic activity and type and volume of magma involved. For example, the large explosive eruption of Mount Pinatubo on 15 June 1991 expelled 3-5 km3 of dacite magma and injected about 20 million metric tons of SO2 into the stratosphere. The sulfur aerosols resulted in a 0.5-0.6°C cooling of the Earth's surface in the Northern Hemisphere. The sulfate aerosols also accelerated chemical reactions that, together with the increased stratospheric chlorine levels from human-made chlorofluorocarbon (CFC) pollution, destroyed ozone and led to some of the lowest ozone levels ever observed in the atmosphere...

Sulfur dioxide gas reacts chemically with sunlight, oxygen, dust particles, and water to form volcanic smog known as vog...

Volcanoes release more than 130 million tonnes of CO2 into the atmosphere every year...

USGS - Volcano Hazards Program http://volcanoes.usgs.gov/hazards/gas/index.php

...............

Chlorine is emitted from volcanoes in the form of hydrochloric acid (HCl), which breaks down into chlorine and chlorine monoxide (ClO) molecules. The sulfate aerosols furnish sites for chemical reactions that release the chlorine atoms. These eruption-derived chlorine atoms are added to man-produced chlorine already present in the stratosphere. The reactive chlorine atoms then proceed to destroy ozone, with each chlorine atom being recycled many times...

Annual contribution not included.
Richard V. Fisher, 1997; EFFECTS OF VOLCANIC GASES; UCSB http://volcanology.geol.ucsb.edu/gas.htm


.................

Water vapor (H2O) is the most prevalent volcanic gas, contributing between
50 and 90% by volume, however the contribution to the global H2O
inventory is negligible in comparison to the atmospheric concentration. The
second important volcanic gas is carbon dioxide (CO2), which ranges from 1
to 40% by volume. Volcanic emissions contribute less than 1% to the total
global CO2 emission (Cadle 1980, Gerlach 1991). Anthropogenic annual CO2
emissions are by a factor of 100 higher than total natural degassing of the
Earth (Schmincke 1993).
Sulfur gases contribute typically 2 to 35%/vol of volcanic gas emissions.
They are the most relevant species concerning the climatic impact of
volcanic events. The dominant sulfur component is sulfur dioxide (SO2), with
yearly emissions ranging from 1.5 to 50 Tg SO2...

Christiane Textor, Hans-F. Graf, Claudia Timmreck, Alan Robock, 2003; Emissions from volcanoes in Granier et al, Emissions of Chemical Compounds and Aerosols in the Atmosphere.

............

[cjl]

Have you allowed for the water vapour content?

I don't think all that much water vapor would be added to the atmosphere. Liquid oceans would still be present. They've been around since well before oxygen was a major component of the atmosphere, so I don't see any reason why they would suddenly evaporate.

[baric]

I don't think all that much water vapor would be added to the atmosphere. Liquid oceans would still be present. They've been around since well before oxygen was a major component of the atmosphere, so I don't see any reason why they would suddenly evaporate.

Right... we might see a general cooling as the oceans draw CO2 out of the atmosphere. We couldn't get a Venus-like pressure until the oceans are gone.

[eburacum45]

but a tentatively estimated 3.6 Tg per year escapes to the atmosphere.

3.6 Tg is 3.6 x 10e9 kg; compared to the mass of the oxygen in the atmosphere, approx 10e18 kg, this is quite small. Other effects such as oxidation of new rock is likely to be more significant. Remember almost all of the Earth's surface is already oxidised, so only newly exposed rock will be oxygen-hungry.

One estimate I've seen is that it would take a million years to remove all the oxygen in the atmosphere- assuming a linear removal, that means 0.1% removal over 1000 years. But there are, of course, many reasons why removal might not be linear.

[cran]

I accept that I overstated the situation at 1000 years.

Without new oxygen production, where do surface water bodies stand as oxygen and CO2 sinks? (I'm reminded of the Toarcian Anoxic Event; and the oxygen excursion associated with the P/T).

What happens to surface erosion without a biosphere?

In terms of breathability, which is more important - mass of oxygen, or partial pressure of oxygen?

Why must evaporation be "sudden"?

[wd40]

Is there any plausible biological (not astronomical or geological) phenomenon, change, damage or extinction eg plankton, forests, hydroxyls, that could alter the atmosphere's % composition sufficiently to endanger human existence in the forseeable future?

[jlhredshift]

I accept that I overstated the situation at 1000 years.

Without new oxygen production, where do surface water bodies stand as oxygen and CO2 sinks? (I'm reminded of the Toarcian Anoxic Event; and the oxygen excursion associated with the P/T).

What happens to surface erosion without a biosphere?

In terms of breathability, which is more important - mass of oxygen, or partial pressure of oxygen?

Why must evaporation be "sudden"?

Indeed, we have in the geologic record of a time before organics. Oceans did exist. Tectonics were active. But that was what, 3.5 Bya, or thereabouts, or more. Water is the most important weathering component for the breakdown of rocks and at some point in the near geologic future a new set of ice sheets will form and scrap off our debris and expose large areas freshly exposed lithic minerals of all kinds to be weathered, abraded, and generally converted to sand, clay, and silt as the ice sheets again retreat. However, the tropics, I am not so sure about.

[eburacum45]

I'm reminded of the Toarcian Anoxic Event; and the oxygen excursion associated with the P/T).

Do we have any figures on how rapid the onset of these phases were? The oxygen content of the atmosphere is so vast only a major event could affect it.

[Ara Pacis]

In terms of breathability, which is more important - mass of oxygen, or partial pressure of oxygen?

CO₂.

[HenrikOlsen]

Right... we might see a general cooling as the oceans draw CO2 out of the atmosphere. We couldn't get a Venus-like pressure until the oceans are gone.

That's a self limiting process, the oceans are already close to equilibrium with the atmosphere when it comes to CO2, they aren't a big magical sink that can keep taking up everything.

[wd40]

Flora exists grows solely because of the 4 parts per 10,000 of CO2 that is constantly being brought to the leaves by wind and air motion.

Vegetation next to motorways is seen to thrive due to the extra CO2 from the vehicle fumes.

Is it possible for excess CO2 to be absorbed in the oceans, or lowered by any other way, enough to inhibit plant growth worldwide?

[tusenfem]

Is there a reasoning behind this questioning? It seems to just be a bunch of questions about CO₂ that seems to be going nowhere. First, will there be a change if mankind disappears until now can it disappear to inhibit plant growth.

Unless you can come up with a reasoning I am closing this thread.