[thedoc (OP)]

James Fowler asked the Naked Scientists:
   A question about dinosaurs and their size, is it possible that millions of years of meteor strikes on earth have made earths mass large enough that gravity today is greater than it was in the time of the dinosaurs and therefore is in part a reason for their large size?
What do you think?

[Georgia]

While the Earth's gravity has increased, the effect is much too small to be an explanation for this.

Alternative explanations: increased oxygen in the atmosphere, needing to be big to digest the tougher plantlife, ecosystems could support bigger animals, efficient bird-like lungs.   

[Tim the Plumber]

Also the strength of earth's gravity is known due to many factors such as the way rocks have been deposited. There has been no significant change.

Animals will often tend to get bigger in stable enviromental conditions which will often tend to give the biggest a breeding advantage over the rest. In more unstable times the capacity of small creatures to live off less food during the bad times kills off the giants.

[evan_au]

the strength of earth's gravity is known due to many factors such as the way rocks have been deposited

Mineral prospectors use gravimeters to measure the surface gravity, to infer subsurface features.

The differences in gravity due to rocks on the Earth today are fairly subtle - they are measured as fractions of a unit called the "gal" (after Gallileo), which is 1 cm/s².

These variations are very small compared to typical surface gravity, which is about 10 m/s².

So this won't cause detectable variation in the size of animals today.

[Tim the Plumber]

the strength of earth's gravity is known due to many factors such as the way rocks have been deposited

Mineral prospectors use [not allowed to post external links. In a science forum???] to measure the surface gravity, to infer subsurface features.

The differences in gravity due to rocks on the Earth today are fairly subtle - they are measured as fractions of a unit called the "gal" (after Gallileo), which is 1 cm/s².

These variations are very small compared to typical surface gravity, which is about 10 m/s².

So this won't cause detectable variation in the size of animals today.

I will try to be more clear;

The way the rocks have been deposited shows how strong the gravity was at the time of deposition. Sometimes.

If gravity had been significantly different the slope of a sand dune would be different for example. It is evidence such as this which allows us to know that it was the same, almost.

[puppypower]

My theory is, the large size of the dinosaurs was connected to the needs of early brain development. The large dinosaur brain was very small in proportion to the body size, with the large body helping the slow proportional brain to progress.

Our modern human brain sits at the top of a feedback loop that integrates the entire body. Every cell of the body, besides blood cells, has nervous tissue nearby for feedback. The brain also controls glands which controls hormones, etc. If the brain feedback was not sufficient to control the body, then the body will not be completely in the control loop. Rather it could play a role that is less subservient and more proactive. The body would be able to push the brain.

In modern animals, nearly all the cells of the body have nerve tissue nearby. This sends control signals to the brain. All our muscles have nerves, some of which contain memories for muscle movement; ganglions. The large body of the dinosaur builds the nervous system, from the bottom up; muscle and body to brain. As the brain gains sophistication and more control in the loop, it can regulates the body better and size begins to decline.

Where this idea came from was base on a science special I watched, that talked about the large size of the redwood trees in California. What is unusual about the redwood trees, besides their huge size, is they grow where the rain is seasonal and unreliable. California has winter rains but summer draughts. The large size was somewhat puzzling. It turns out the redwoods are located near the Pacific ocean and gain most of their year round water from ocean humidity, which is drawn in through the leaves. In the hot dry summer, they drink water by the leaves.

Instead of the roots driving the water uptake,which is more normal, the leaves do the bulk of the water uptake. This water uptake by the leaves, allows even the roots to grow. The growing roots then can then find scarce water and drink in the winter rains. Life is designed with control loops, with the redwood showing it is possible to use another aspect to lead the loop. Their large size is due to the loop being rotated. 

Consider the dinosaur, with a growing body that is generating local nervous tissue connections, from the bottom up; body to brain. If you had more nervous control via the body, compared to the brain, conscious body actions would be very simple and basic, but they could be very fast and very powerful due to the body nerves.

The raptors, which are considered very intelligent, had a brain that would regulate body size. They had reached the point where the brain was at the top of the loop.

[JoeBrown]

Evolution astounds me...

I find it hard to believe life evolved, yet everywhere I look, I see more and more evidence that not only supports the theory, it also suggests that individual organisms experience their own individual "micro" evolution.  Human ability to assimilate information has evolved during my lifetime, at a somewhat alarming rate, akin to a feedback loop, that's exploding into artificial intelligence.

When contemplating Dino the dinosaur's evolution, you might reflect on abundance of food and also the fact that in all probability, the variety of foods available were more limited.  Essentially the gene pool way back when was considerably more limited, or the bulk of the gene pool foods (raw plant proteins) were different variety than the present variety.

I'm fairly confident that mammals didn't evolve until tree nuts (concentrated protein) were plentiful.

That's my guess.  I'm no scientist, but it seems reasonably logical (to me).