I was wondering what would happen to life, when an infamous epidemic plague would be able to infect and kill any imaginable plant, be it on land or in the waters.
Would the lack of oxygen eventually kill Earth's fauna? Or would a gradually fading out food production be the bottleneck?
(Edited as per comments, thank you!)
Lack of oxygen won't be a concern, we got enough for millions of years. Sure it will run out eventually but not for a long time. So yes eventually it would kill Earth's fauna but not before evolution could make a dent in it.
Food supply will indeed be a much larger issue. Within days to weeks the majority of herbivores will start to die from malnurishment. Remember that it's generally the carnivores that do well without eating regularly. Plant matter is much harder to digest and generally requires a much larger portion of the day directly dedicated to eating.
So with a large portion of the herbivores dying there will be a surge in available food for carnivores. But this will quickly rot and then starvation will set in for our predators as well.
Within months the majority of species will have simply died off. The rest will likely quickly follow. Seas will become cesspools of disease and toxins. Humanity will be among those that die out. We can't survive on a diet of pure meat. Long term storage of food will remain for a long time if limited to a small group of consumers.
There are a couple ecosystems that don't use photosynthesis to supply all their energy. These get their energy from heat-loving bacteria that live on underwater volcanoes and get their energy there. These ecosystems are very deep in the ocean and include worms and blind crabs.
What humanity will do, there is no objective answer here. Will we die out? I see it likely if we can't regrow any plants ever.
and generally requires a much larger portion of the day directly dedicated to eating. Very true; my mom owns horses. Horses--as an animal--are designed to eat 23 hours a day (cows are probably similar). If their stomach ever gets full, they empty it. Exercise for the reader: how do you keep a diabetic horse from eating too much?
– Draco18s no longer trusts SE
May 08 '17 at 13:41
Most of the oxygen is not produced by plants, but by ocean algae. What is produced by the rainforest is used locally too — and since all the animals there will die, it comes out even.
You didn’t indicate whether seeds and spores were affected, so I can’t contemplate a timeline of what happens next.
Would the lack of oxygen eventually kill Earth's fauna? Or would a gradually fading out food production be the bottleneck?
The latter, oxygen would last a lot longer than food.
Your earliest ones would probably be herbivore mammals on land. These need to eat constantly just to survive. Some reptiles will last a long time, perhaps years and some insects will be among the last of all to die off because they feed on animals.
Sea life is an unknown, most fish won't last long, because a huge amount of fish live on algae, so eventually the food chain will break down in the sea. With scavengers like crabs and deep sea animals feasting for decades.
Life will still exist deep under the sea in places with ecosystems that are based on bacteria that process vent chemicals etc,. Unless you class those bacteria as plants.
All in all it wouldn't destroy life totally, and even some of the eventual extinctions might take 100 years or more to come about.
An epidemic kills all plant-life on Earth. What would happen to the fauna? Is there some realistic time-line when happens what?
Epidemics are spread from one organism to another which make them virtually incapable of ending all life regardless of how virulent they are. Instead you will see an initial period where the die off of plant life is slow. As the epidemic spreads the depopulation of plants will rapidly speed up as the epidemic becomes a pandemic.
As plants die off, animal life will follow in proportion to how quickly plant life is dying off following a latency period as thier stored calories diminish.
Eventually the sickness will start running out of places to spread and then the epidemic itself will die off. Places that were once rich in life will be totally wiped out, but in remote places like deserts, islands, and mountain tops there will still be pockets of surviving plant life where the epidemic did not have the means to spread to, and animals to take advantage of said plants. At this point, life will balance until the epidemic itself is extinct allowing the remaining plant and animal species to eventually begin spreading out again.
As has been pointed out, food will give out long before the oxygen does.
However, there are a few microbes that get their energy from the chemicals released by the undersea vents. The ecosystems that revolve around them may survive. However, I am not postitive about that they can survive without the "snow" of organic particles that rain down from the higher layers of the ocean.
There is also a type of bacteria that actually gets its energy from radiation. So far, these are only found underground and are not part of any ecosystems that I am aware of.
So, almost all life on the planet would die but that has happened a number of times in the past. The survivors evolved, spread and multiplied to give us what we know. It is likely to happen again. However, if an intelligent species develops again, it is likely that they will be in a situation where the Sun would be near exhaustion.
If the plant killing is very sudden you'll have an excess of oxygen from what they (the plants) stop conssumming. But microbes will conssume that while they feed on the detritus, therefore causing a step increase in methane all over the world, to the point where the globe will become little less than a fetid swamp.
Lighting will eventually lit the methane and whatever dry organic material will spark fires (conifers and tundra specially) creating CO2 and CO in excess, probably causing most of the fauna extinction by gas poisoning and ash fallout. Others will die from ramping diseases (I'd assume from the abondance of microbes). Maybe extreme desert fauna could survive this?
Fungi should also thrive in mist of the organic waste and so a few insect species feeding on them.
This is basically what happened at the Cretaceous-Tertiary extinction, and as a result the timeline of events for what would likely happen has been discussed to some detail in the scientific literature. Basically, nothing grew for years after the impact, most plant life on earth survived as seeds during this time. However, I cannot find a more specific estimate for how many years it took for new plant life to grow, I would assume at least two based on the link but I have heard estimates of up to a century before plants started growing again (though it would be cool in an apocalyptic way, I am a bit skeptical of this).
The general timeline of events is that herbivorous animals would have started dying out first, due to the loss of their food source. Carnivores would last longer, because they would be able to scavenge on carrion and feed on each other, but eventually they too would eventually dwindle and die out due to lack of food. Larger species would die out first. The animals that survived the K-T the best were those that were part of brown food webs (i.e., rivers) based on the breakdown of detritus as a primary food source rather than green plants, or could switch to feeding on aquatic prey. Others, like mammals, likely hibernated through the extinction (or fed on seeds).
The only difference is in your scenario the plants never came back. Eventually the brown food webs would fail because there was no longer organic matter being introduced into aquatic ecosystems. Small hibernators would wake up only to starve to death in the absence of food. Given that all plant life on Earth was nearly wiped out by the K-T extinction and yet we didn't all choke to death, it seems safe to assume that everything would die of starvation long before any lack of oxygen.
The question is are you counting non-plant photosynthesizers like cyanobacteria, algae, and phytoplankton as plants. Marine photosynthesizers produce 85% of the world's oxygen, and if you only wiped out all land plants life on land would be devastated but aquatic life would eventually continue with little change.
