Ecosystem Recovery after Extinction Event

[Grimbear]

Ok, am seeking the assistance of a scientific prodigy/knowledgeable amateur...

On the planet the settlers in my novel have begun to colonize, there has been in the past an extinction event similar to the one that put paid to the dinosaurs. My idea is that it there was an asteroid that collided with the planet.

I have two questions:

1 - How long ago could it have been? The atmosphere is clean and plant-life has recovered, but there are still no large animals, at least on the one continent. My idea is that the largest animals on land are about the size of sheep or goats - smallish herbivores. How long after an extinction level asteroid collision would this be? 100,000 years? 500,000 years.

2 - What would the point of impact look like now? Could it be a large valley - retaining some of the appearance of a crater?

All opinions (esp if they match) gratefully received,

Thanks

Grim

 

[J Riff]

There's data up the yinyang but everything depends on the force of the impact, the dust cloud, the tsunamis and the heat wave.
I watched the documentary on the Gulf of Mexico meteor, which killed most of Earth's dinos, possibly. It was pretty detailed, down to the effect thousands of miles away, and what would survive, I'd give it a look if you can find it.

 

[psychotick]

Hi,

I hate to tell you this but it all depends. How big the asteroid was, how severe the damage. The thing that likely killed off the dino's was in fact the dust, tossed up into the atmosphere by the blast it stayed up there for many years, decreasing the amount of sunlight reaching the ground, reducing temperatures and killing off a lot of plant life. The Dino's found themselves in a bad state of affairs as they ran out of food, the herbivores starved which meant that in turn the carnivores starved, and you had an ecological melt down. Add to that the fact that they were cold blooded (there are some disagreements about this), and you have a recipe for a disaster.

Now mammels survived being warm blooded, and at the time, also being small and adaptable. They weren't at the top of the food chain which was the most vulnerable, and they essentially scavanged until things improved, and then found themselves with an entire new world they could colonise. Loads of new ecological niches they could fill. But the evolution to do that required millions of years.

Now in your scenario world you have to ask yourself - how severe was the damage? How much of the top level ecological strata was wiped out? How advanced were the creatures that survived? If the top level survivors were single celled organisms, then you're looking at at least hundreds of millions of years to reach sheep. If they were rodent like critters, not so long.

But still evolution is not fast, so at a minimum count on millions of years.

Cheers.

 

[chrispenycate]

If there is a population of herbivores there has to be a set of predators keeping their numbers down and their quality up; perhaps as big as cats or foxes, for your example. If starvation and disease were their principal means of herbivore control they wouldn't have grown bigger; and I'm assuming they survived because of underground habits, like gophers or something? So probably not much bigger than a rabbit. I'd expect that adapting to the newly available ecological niches and increasing size generation after generation would take at least a couple of million years; unless, of course, the continent was scoured clean and they migrated in from somewhere else; I could see seals (or dugong, if you want herbivores) recolonising the vacant land, regressing to skills lost for thousands of generations, but still in the gene pool; clumsy, obviously, but there would be nothing to compete with them. That would require less size increase.

As to the size of the colliding object, it wouldn't have to be too enormous; maybe the size of Wales, but more likely Skye. Indeed, if it were much bigger it wouldn't leave a crater, but an ocean. A lump the size of Skye wouldn't contain enough energy to do such a comprehensive scouring, so perhaps the asteroid contained a largish concentration of some chemical poisonous to animal life forms, vaporised and carried round the world by the violently disrupted winds. Or the larger animals had become too seasonally specialised, and dust cutting off the sunlight unbalanced their rhythms. Oh, flaming shockwaves, earthquakes and disrupted water would kill hundreds of millions, of course, but disaster statistics show there are always freak spots where there are survivors - generally a population large enough to regenerate, in time (rather less time than developing whole new species; thousands of years, not millions).

 

[Nik]

IMHO, a lot depends on the climate zone that the impactor hits. If there's a reasonable amount of sun and rain, and the weather is moderate, wind-blown seeds will recolonise in a few centuries at most. Erosion will begin to smooth the crater rim, back-filling the centre...

However, the tectonic upset of an 'Extinction Level Event' is likely to leave hot springs and such-- Think Yellowstone's caldera.

IIRC, full speciation among survivors will take several million years to get going, although the 'Founder Effect' of genetic drift among isolated groups may change their morphology sooner...

 

[Jake Reynolds]

It may also be worth considering whether the planet is M Class or terraformed. That may give you some scientific leeway.

 

[Grimbear]

Thanks for your answers - very informative and helpful.

This is what I'll go for:

2 million years approx previous - small asteroid hits planet near the centre of a large continent the size of say Africa which is centred on what would on Earth be the tropic of Capricorn. At the time this is forested and mostly temperate, colder in South nearer the pole. Ensuing dust creates inhospitable environment. Dark and overcast skies cause plant death. Small mammal-like creatures hang on by a hair's breadth, scavenging and living in burrows etc.

The other continent is not so affected, being on the other side of the globe, but most larger animals also die off here.

Sea-life less affected, but still I'd imagine food scarce enough for long enough to cause the deaths of many species due to a dying-off of photosynthesizing organisms.

2 million years later plant-life is back in force and settlers arrive to colonise this M Class planet. There are still only small animals - small wild-cat-like and ferret-like carnivores, smallish goat-like herbivores.

The other continent - should anyone go there, will only have slightly more variety and animals only up to say the size of say an eland or duiker.

Does this sound feasible?

I'm not going to be very specific in the novel.

Thanks again everyone!

Grim

 

[Grimbear]

Not 2 million years - I'll say 4 million. Sounds more likely, from your replies, to be longer rather than shorter.

Thanks,

 

[Stephen Palmer]

This...

http://www.amazon.co.uk/dp/050005116X/?tag=brite-21

... is probably the best book I've read on the subject. Enjoy!