What if all land-based life was exterminated by a virus?

Question

I'm writing a short story where a virus(partly magical btw - it's fantasy genre) eradicates all life on earth, except marine-based life, meaning the seas and lakes. I'd like effects of such an event to be realistic to an extent. So, here's how I'm thinking - no more land-based creatures to breathe and produce Co2 and no more trees to make O2. Taking into account that all is land based flora and fauna is dead - would lands thus be covered in dust? Do you think such a world would cool down? (no more methane, C02 to be exhaled by most creatures - an ice age?). Many organisms in the seas produce oxygen, but do you think that would suffice for the air to be still breathable to humans? How would such an event affect the four seasons? I'm sure I didn't thought of some logical effect of such a thing, so all ideas are welcome.

Answer 1

1) With no plants to hold down the soil, I do think that the land would be covered in dust.

2) I'm not sure as to whether much cooling would occur (there would still be solar energy heating the earth and water vapour etc to retain heat, plus I don't think life is essential for a warm environment, although some degree of cooling *might* occur I suppose), but don't think there would be an ice age (the ocean currents would still be working, and I don't think that life is what prevents the earth from becoming icy at all).

3a) The sea organisms probably would not  produce enough O2 to support humans on the level we're familiar with (although there could be enough O2 to support some people), but aren't the humans extinct too, since they're land-based life? :)

3b) However, the air is roughly 20% O2 and killing all the plants shouldn't remove the oxygen from the air, so from that angle, people could probably be supported until enough O2 is used to cause people to die from oxygen starvation.

4) The seasons should be pretty much the same as seasons are a product of the Earth's movement around the sun and how it is tilted on its axis at any given time of the year (e.g. when N part of axis is further away from the sun than the S part of the axis, the southern hemisphere will be experiencing a warmer season).

NOTE: I know you said that your story is in the fantasy genre, but viruses are generally species specific - it's rare for a virus to be able to affect multiple species, and I don't think anything currently known to us is capable of wiping out people, animals, and plants. Just something for you to be aware of, although your magical virus could be the first! :)

Answer 2

Worse -- all of your sea life would die from starvation and lack of oxygen.

In terms of the Food Chain in the ocean, a lot of the low-level  animals feed off of the dead plant and animal life that washes into the ocean from the rivers.

While there would initially be an abundance of food (as dead plants and animals floated down to the ocean) this would eventually stop.  So the lower life forms would starve to death.

But the higher life forms eat the lower life forms. so as the lower life forms starve, so will the higher life forms.

Consider, too, that some animals like whales and dolphins breath air.  They NEED the oxygen produced by the on-land plants.  Without oxygen, marine mammals are going to die pretty quickly, too.

Now, with no land plants to hold the soil in place, rains are going to wash the soil away in a mass erosion.  And all of this ends up as mud in the ocean.  That reduces the oxygen levels, and more sea life dies. (This is happening now in the Gulf of Mexico due to the spring floods in Iowas and Illinois).

Fact is, our ecology is an extremely tightly intertwined network.  Mass extinction of lands based life would all-too-quickly result in the death of all marine life as well.

Answer 3

Doesn't work that way... first of all, plants wouldn't die off if there were no more land mammals, there are other sources of CO2.... the oceans for example release a lot every day..... when something dies it also releases CO2.... second, the world will probably not cool down because water vapor is actually the number 1 greenhouse gas and the ocean has a lot to do with Earth's temperature.... Third, there is a tremendous amount of oxygen in the air and i don't see that decreasing any time soon, so the air should be breathable to humans..... Fourth, the seasons are created by the Earth's tilt and its distance from the sun.