[KarlInOhio]

They think the supernova exploded 250 light-years away from Earth,

If a 10 solar mass star's entire substance were distrubuted evenly over the surface of a sphere 250 light-years across, you get (2 x 10^31 kg) / 4pi*(2.37 x 10^15 km)^2 = 0.283 kg/km^2 or about a quarter milligram for every square meter.

In reality, most of that is hydrogen and helium, not heavy metals, it won't all come at once, and not all of it will escape from the supernova's core's gravity.

Which is more believable, all the large North American mammals were killed by a quarter milligram per square meter of material spread out over years, or the arrival of humans on the continent?

[spunkets]

I get 1.14mg/m² and 56 MJ/m. That's 56 megajoules of kinetic E/meter². Also, all of a star's fuel is used before it goes supernova, so the frag is heavy elements, not H and He.

[Bernard Marx]

Which is more believable, all the large North American mammals were killed by a quarter milligram per square meter of material spread out over years, or the arrival of humans on the continent?

Why did the humans kill only animals that weighed over 250 pounds, on average? There may be an explanation but as the article says:

"What is exciting about Dr. Firestone's theory is that it can be easily tested," Becker said, and indicated she hopes future research will yield additional clues from North American and other sediment layers."

I'll wait for the research.

[MHGinTN]

You make a false assumption, that the material of the star would be evenly ejected and have no clumping.

[lmr]

Which is more believable, all the large North American mammals were killed by a quarter milligram per square meter of material spread out over years, or the arrival of humans on the continent?

You are absolutely right, and your example requires a star 10 times bigger than our sun.

Large brained humans hunted these animals for food, as humans propagated the numbers of these large animals diminished. Another good reason these animals were hunted was to keep their numbers down for safety, they were way too big for humans to peacefully co-exist with them.