Occasionally, every X million years or so, the Earth is slammed by a extraordinarily large and fast comet or asteroid. The land shakes violently, tsunamis scour the coasts, falling debris heats the air and pummels the ground. The resulting dust storms will likely induce an ice age.
For perhaps hours or days the temperature of the atmosphere is raised in some places as high as that of boiling water, followed by several years of freezing dark. A majority of species, and most life will die.
Can we do anything? Consider the aftermath. Any surviving animals, be they insects, chipmunks or people, that crawl out of the ice will face a bare and chilly world without food or shelter. Encouraging quick plant growth should be our main concern.
I'll concentrate on a way to preserve seeds through this period to establish a new ecosystem as soon as possible.
As an idea, imagine an amalgam of manure and straw, in the form of a ball, with the seeds mixed in (feel free to imagine other possible compositions). Dip it in some insulating foam to allow it to survive the heat and cold, spread them far and wide and wait for things to warm up again. They should be designed to disintegrate when wet, allowing the seeds to sprout and grow, yet not fall apart prematurely.
One way to test seedballs is to make differing batches, bake them in a oven for a day and store them for a year or more in a freezer. Set them out on some soggy, ash choked piece of ground and see what happens.
The first generations of seedballs won't work very well. Assembling something that can protect seeds for so long at such temperatures is probably difficut. No seeds, or at most a very small percentage will live to germinate.
Several generations of testing may be necessary before a combination of materials and seeds can be found that has a chance of success.
However, even a poor seedball could be viable with some cover. Bury them under a little soil or toss them in a lake and they might survive post-impact conditions quite well.
Of course, the ideal is a seedball that is inexpensive to make and easy to distribute. If they can be frozen for years, so much the better. Take them out when needed. They could also be spread around at any time, as they are made, even if no particular threat loom. If they germinate, no big deal. If disaster strikes unexpectedly, we are that much better prepared.
Imagine a time when we do not have a significant space presence but we detect the inevitable comet en-route to a meeting with our vulnerable planet. We may have years to prepare, or we may have only days. There is no chance of diverting catastrophe, only, perhaps, one of easing the aftermath.
The cost of preparation can be relatively cheap. Of course, grant money can be sent to various universities to investigate seedballs and other possible interventions and it may be a good investment. However, I think an X Prize might be a more efficient spur. After all, the research seems to be fairly inexpensive; seeds and soil, ovens and freezers; nothing very high tech. Anyone can play and the prize need only be paid out for success.
A few million dollars spread out over several decades might be money well spent. The end of the world will be a much more expensive proposition.