[varmintman]

I've always wondered why some animals in ancient times were so much larger than today. Was it because their predators or their prey was larger, sort of like an arms race?

One word: gravity..... It's a fairly easy demonstration that the larger dinosaurs could not function in present gravity. There are different theories as to why gravity might have been different in ancient times.

[Smokin' Joe]

It's a fairly easy demonstration that the larger dinosaurs could not function in present gravity.

Maybe they were 'light in the loafers' (which might help explain why they died out...)

[Sudetenland]

LOL!!! There could not have been any change in gravity on Earth for billions of years, far-far-far ahead of any life appearing. Gravity is solely a function of mass and the mass of the planet hasn't changed markedly since its initial formation.

No, there was no gravitational change associated with the extinction of dinosaurs.

[FreeAtlanta]

could not function in present gravity

As crazy as that sounds, I have often wondered if gravity would have a big impact.

The Earth adds mass continually from space dust and meteors;

The Earth gains mass each day as a result of incoming debris from space. You may have even seen evidence of this activity in the form of a 'falling star', or meteor, on a dark night.

While the actual amount of added material depends on which study you look at, an estimated 10 to the 8th power kilograms of in-falling matter accumulates every day. That seemingly large amount, however, IS insignificant compared to the Earth's total mass of almost 10 to the 25th power kilograms.

In other words, Earth adds an estimated one quadrillionth of one percent to its weight each day. I don't know of any counteracting mass LOSS mechanism of any consequence.

I have never done the numbers to figure out how much gravitational impact that would be on large animals and vegetation.

[Battle Axe]

There was more oxygen back then. There were more trees and more photosynthesis, thus more oxygen. All the CO 2 was used up and sequestered in the plants.....then the comets came....and smacko.....