1st Meteorites from 1908 Tunguska Explosion

[JamesSavik]

1st Meteorites from 1908 Tunguska Explosion

https://weather.yahoo.com/1st-meteorites-1908-tunguska-explosion-possibly-found-155101604.html

In June 1908, a mysterious blast occurred above the remote Russian forests of Tunguska, Siberia, with 1,000 times more power than the Hiroshima bomb, flattening trees over an area roughly the size of Tokyo.

[Trab]

Interesting.

I've wondered for many decades how many of the roundish, crater-like, lakes and bays scattered around the globe will eventually be recognized as impact craters. I know several already have, like the gigantic one by the Yucatan. Sometimes a volcanic eruption (explosion) can seem similar, but the geology is usually much different.

If one uses Google Earth to just scan the planet, one can be amazed by the numbers of nearly circular depressions with nearly centralized upheavals (seen as an island) indicative of an impact. There are small ones, relatively, like Ungava in Quebec, but I suspect some of the large ones as well, like James Bay off Hudsons Bay, and maybe even Hudsons Bay. I've seen similar things on other continents too. It would be nice to know what really happened, but I doubt it will be proven in my lifetime.

[JamesSavik]

Our planet is lucky. Compared to other objects in the solar system, we haven't been pounded like Mercury or even our own moon. Those bodies with no hydrosphere or atmosphere don't have a weathering mechanism to hide those scars. All of the inner solar system took a beating during the early and late bombardment periods. Our planet's crust is dynamic enough to be able to hide the worst of it.

There are two big factors in our favor. We have a relatively large moon which complicates the trajectories of incoming objects. Jupiter has done a good job of sweeping up most of the strays in the middle orbits with its massive gravitational field. We still catch the random stray but we aren't being constantly pounded.

There are a number of impact craters that have been identified- some only by satellite imaging. I think the number stands around ~250. There are some big ones in Canada.

Some are very, very large, old and quite weathered.

The way that you can tell the difference is that volcanic activity is pretty distinctive.

Impact craters have "shocked rocks" or rocks that bear the very specific signature created by an impact.

I think there is actually a tour of impact craters of the world on google earth. It's been a few years ago, I remember paging through it.

[Rutabaga]

When I was in college there was a lot of currency to a theory that a massive meteor impact years ago actually caused the earth to wobble in its orbit, altering the climate dramatically and killing off the dinosaurs. This same theory held that this impact altered the number of days in a year.

R

[Nigel Gordon]

When I was in college there was a lot of currency to a theory that a massive meteor impact years ago actually caused the earth to wobble in its orbit, altering the climate dramatically and killing off the dinosaurs. This same theory held that this impact altered the number of days in a year.

R

I think there is still a lot of currency to that hypothesis though I don't think that it was the dinosaurs that got wiped out, that I believe is the Yucatan impact which is somewhat later.