I read in a book that earth was smaller in the past (they dont give any explanation for this fact). Why? Why was smaller? How much? Where can i get a "cronology" for the size of the earth (something like: at 520 milions earth diameter was 10000km, at 200 was 11000 km, etc).

Could that be an explanation for the huge size of dinossaurs?


If you know a good source for such info i would aprecciate.

thanks

locked

Origin of the Concentric Layering
The earth grew from the accumulation of planetismals (meteorites and asteroids), over a period of 1-200 million years about 4.3 to about 4.5 billion years ago. Toward the end of the accumulation a large mini-planet hit a glancing blow with the earth. If the mini-planet had hit directly the earth would have been shattered, and the debris scattered throughout the solar system - no earth (gee, are there not movies on just this theme? Deep Impact comes to mind). As it was, the mini-planet hit obliquely, and then spun off into an orbit around the earth - to become the moon.
If the earth had grown simply from the random accumulation of planetismals it would have been homogeneous - more or less made of the same material throughout, and the earth cross section to the right would be a uniform blob with no structure.
But the earth is stratified into layers by density (heavy core, intermediate mantle, light lithosphere), telling us that early in its history the earth went through a molten stage that led to the heavy materials sinking inward to form the core, and the lighter materials floating toward the surface like a slag to form the crust. The heat for this melting came from meteorite impacts, the moon's impact, and the decay of radioactive elements.
Imagine flying by the earth in a space ship about 4.3 billion years ago; all you would see is a glowing red hot ball of seething magma.

http://csmres.jmu.edu/geollab/Fichter/PlateTect/heathistory.html

The planetismals and the moon explain the difference in size, at some billions of years ago (dont have sure about the moon..the age of the hit). The difference in size that i am speaking about its more recent than the impact of the moon or planetismals. In the book (its a kind of enclopedia) that i spoke, they refer to 200 000 000 years ago(since american and european numerica system are different i will post the entire number)...thats very little time in the history of Earth. The book speaks that the continents were together in the past (as we know) at 200 000 000 and in that time earth was smaller. Then, with the growing up of size, and with the tectonic movement, the continents started to sperate from each other.

So, about the size due to the moon impact and planetismals (at about 4000 000 000) i already knew, what i didnt knew (and whats i ask here) is that thing about the size of the eart growing up like a balloon.

There is a theory that all the water in the oceans came from ice comets. The size of dinosaurs may have to do with the higher oxygen content in the atmosphere at the time.

How does oxygen (and noble gases, like Dwayne said) relat to the huge size of dinossaurs?

And i dont think that the size of planet (the size that i spoke about....at about 200 millions years) its due to the comets..just what i think.


btw, i never heard about that theory about the comets. I think thats to much water for the comets to bring to Earth...maybe, lets say, 5% of the water in the planet its because of comets but the rest...i dont know. Anyway, i dont understand almost nothing about such topics, so i cannot speak :D

How does oxygen (and noble gases, like Dwayne said) relat to the huge size of dinossaurs?

And i dont think that the size of planet (the size that i spoke about....at about 200 millions years) its due to the comets..just what i think.


btw, i never heard about that theory about the comets. I think thats to much water for the comets to bring to Earth...maybe, lets say, 5% of the water in the planet its because of comets but the rest...i dont know. Anyway, i dont understand almost nothing about such topics, so i cannot speak :D

Hello kazbadan,

From what I recall from geology, there's nothing to indicate the Earth grew any to speak of during that time. We do gather something over 100 tons of cosmic dust each year but compared to the mass of the planet that still doesn't amount to much even over long periods of time.

Also, the idea put forth about the planet expanding and contracting is pure fantasy. And so is the business about the nobel gasses affecting animals' sizes. I'm a biologist (marine) by profession and I can state - professionally - that supposition is utter nonsense.

Comets as a source of water, however, IS accepted as possibly a good theory. The primary question remaining, though, is in what quanitity?

Greater amounts of oxygen would support larger creatures, at least in theory.

Greater amounts of oxygen would support larger creatures, at least in theory.

Yes, at one time that was thought to be true. However, most biologists abandoned that theory long ago. Today, the two factors that play the most prominent roles in determining maximum animal sizes are considered to be food supply and metabolic rate. As a very rough example, consider what you know about whales and hummingbirds. :)

Ice core samples indicate that except for CO2 levels, the composition of the atmosphere has changed very little over eons.

I was curious about that question on the size, because i read it in a book similar to an encyclopedia.

Thanks for your answers :)

Ice core samples indicate that except for CO2 levels, the composition of the atmosphere has changed very little over eons.

Interesting that this should be brought up now. There was a paper in the latest issue of Science dealing with just this issue.

Falkowski et al., The Rise of Oxygen over the Past 205 Million Years and the Evolution of Large Placental Mammals, Science 2005 309: 2202-2204 (http://www.sciencemag.org/cgi/content/abstract/309/5744/2202)

(You of course need a subscription to view the online paper, so I'll copy the abstract here. Hope it's kosher to do so.)
On the basis of a carbon isotopic record of both marine carbonates and organic matter from the Triassic-Jurassic boundary to the present, we modeled oxygen concentrations over the past 205 million years. Our analysis indicates that atmospheric oxygen approximately doubled over this period, with relatively rapid increases in the early Jurassic and the Eocene. We suggest that the overall increase in oxygen, mediated by the formation of passive continental margins along the Atlantic Ocean during the opening phase of the current Wilson cycle, was a critical factor in the evolution, radiation, and subsequent increase in average size of placental mammals.

The paper references other papers with models based on "analyses of the isotopic composition of carbonates and sulfur or on the relative abundance of different rock types." And which "suggest that atmospheric oxygen concentrations varied throughout the Phanerozoic, with a maximum ~300 million years ago (Ma), a minimum ~200 Ma, and an overall rise from ~200 Ma to the present."

The paper in question combined these results with analyses of their own of the "isotopic record of organic carbon" of the last 205 million years.

The results suggest that oxygen levels have doubled in that time.


The paper mainly speaks of the possibility of the oxygen rise being beneficial to larger mammals (to take advantage of the depletion of reptiles at the KT event). But, it does mention that the decline of terrestrial animals at the end of the Permian and early Triassic coincides with a period of sharply declining oxygen levels and that "the rise of oxygen over the ensuing 150 My almost certainly contributed to evolution of large animals." (Both therapods and mammals (although the mammals had to wait until KT to be able to really take hold.)

All off-topic of course.

So, the large amount of oxygen can be a possibility for explaining the huge size of dinossaurs. I didnt knew that in the past the amount of oxygen was that high, very intereting. I just dont still get how exactly the amount of oxygen means bigger creatures. Some of you said that great amount of O2 can support bigger creatures, but how does that happen? And why did the oxygen level decreased to a minimum at 200 m.y. ago? Btw, was that the factor responsible for the vanquish of dinossaurs?

Coming back to the topic, in the book (the one that spokes on the size of the earth in the past) says that there are some evidences that indeed earth diameter was not so big as now. I wonder what kind of evidence is that one. In the other hand, if we suppose that such theory is correct, dinossaurs make sense: less gravity means bigger ceatures (or is the opposite?).

Interesting that this should be brought up now. There was a paper in the latest issue of Science dealing with just this issue.

Falkowski et al., The Rise of Oxygen over the Past 205 Million Years and the Evolution of Large Placental Mammals, Science 2005 309: 2202-2204 (http://www.sciencemag.org/cgi/content/abstract/309/5744/2202)

(You of course need a subscription to view the online paper, so I'll copy the abstract here. Hope it's kosher to do so.)
On the basis of a carbon isotopic record of both marine carbonates and organic matter from the Triassic-Jurassic boundary to the present, we modeled oxygen concentrations over the past 205 million years. Our analysis indicates that atmospheric oxygen approximately doubled over this period, with relatively rapid increases in the early Jurassic and the Eocene. We suggest that the overall increase in oxygen, mediated by the formation of passive continental margins along the Atlantic Ocean during the opening phase of the current Wilson cycle, was a critical factor in the evolution, radiation, and subsequent increase in average size of placental mammals.

The paper references other papers with models based on "analyses of the isotopic composition of carbonates and sulfur or on the relative abundance of different rock types." And which "suggest that atmospheric oxygen concentrations varied throughout the Phanerozoic, with a maximum ~300 million years ago (Ma), a minimum ~200 Ma, and an overall rise from ~200 Ma to the present."

The paper in question combined these results with analyses of their own of the "isotopic record of organic carbon" of the last 205 million years.

The results suggest that oxygen levels have doubled in that time.


The paper mainly speaks of the possibility of the oxygen rise being beneficial to larger mammals (to take advantage of the depletion of reptiles at the KT event). But, it does mention that the decline of terrestrial animals at the end of the Permian and early Triassic coincides with a period of sharply declining oxygen levels and that "the rise of oxygen over the ensuing 150 My almost certainly contributed to evolution of large animals." (Both therapods and mammals (although the mammals had to wait until KT to be able to really take hold.)

All off-topic of course.

That IS new and interesting! If it can be verified it will result in a lot of rethinking of currently held positions.

I read in a book that earth was smaller in the past (they dont give any explanation for this fact). Why? Why was smaller? How much? Where can i get a "cronology" for the size of the earth (something like: at 520 milions earth diameter was 10000km, at 200 was 11000 km, etc).

Could that be an explanation for the huge size of dinossaurs?


If you know a good source for such info i would aprecciate.

thanks

I am no scientist but as far as I know (and which makes far better sense to me than the oxygen level business) is that the maximum practical size of an animal is determined by the strength of gravitation. At present an elephant has about the maximum size for a land living animal, a whale can be bigger because the effect of gravity is less in water. Insects have a much smaller maximum size because the external skeleton is weaker. You also have to take into account the strength of the heart required to pump blood through the body. The size of dinosaurs would suggest that the earth should have been bigger at that stage, a greater size with the same mass would render a weaker gravitational force on its surface.

I hear the proto-earth sometime before 3 billion years was bombarded by another mars-sized planet called 'Orpheus', according to a television program. This would probably account for the larger radius.

But for the specified dates (e.g.200MYA), how do they arrive at these conclusions? In order to increase the radius by a full 500km (volume computation), you'd have to bombard earth so many times that we, nor any other life form, wouldn't really exist.

You can discount solid compression, since earth isn't really massive enough to do that.

Gas evolution? No... no seismic evidence indicates large-scale porosity (maybe the core, but that doesn't provide 500km of expansion)

Venus-style tectonic makeover? No... we have cratons.

Liquid evolution? For achieving expansion in volume, this would only be applicable to the rocks and not water. Which means large amounts of heating. But still not enough for 500 km imo w/o disrupting the "geological consent" on the presence of life.

I can't think of anything else.


Let me suggest something. We have (or have had) large animals the size of mammoths and giraffes which stand up to 30ft tall for extended periods of time. I believe that most dinosaurs, when positioned horizontally, didn't stand far above 30 ft. It's best to get the kindergarten picture of upright godzilla-like dinosaur clay figurines out of our minds, since it's rather erroneous and misleading. Even the T.rex stood bent over horizontally.

I hear the proto-earth sometime before 3 billion years was bombarded by another mars-sized planet called 'Orpheus', according to a television program. This would probably account for the larger radius.

But for the specified dates (e.g.200MYA), how do they arrive at these conclusions? In order to increase the radius by a full 500km (volume computation), you'd have to bombard earth so many times that we, nor any other life form, wouldn't really exist.

You can discount solid compression, since earth isn't really massive enough to do that.

Gas evolution? No... no seismic evidence indicates large-scale porosity (maybe the core, but that doesn't provide 500km of expansion)

Venus-style tectonic makeover? No... we have cratons.

Liquid evolution? For achieving expansion in volume, this would only be applicable to the rocks and not water. Which means large amounts of heating. But still not enough for 500 km imo w/o disrupting the "geological consent" on the presence of life.

I can't think of anything else.


Let me suggest something. We have (or have had) large animals the size of mammoths and giraffes which stand up to 30ft tall for extended periods of time. I believe that most dinosaurs, when positioned horizontally, didn't stand far above 30 ft. It's best to get the kindergarten picture of upright godzilla-like dinosaur clay figurines out of our minds, since it's rather erroneous and misleading. Even the T.rex stood bent over horizontally.

Thanks for the reply, I cannot realy answer your quetions, this is a little over my head. The fact remains that there is no physical advantage (if not at all impossible) for an animal to be substantially larger than an Elaphant to live on land on an Earth at its current dimensions.

I read in a book that earth was smaller in the past (they dont give any explanation for this fact). Why? Why was smaller? How much? Where can i get a "cronology" for the size of the earth (something like: at 520 milions earth diameter was 10000km, at 200 was 11000 km, etc).I was curious about that question on the size, because i read it in a book similar to an encyclopedia.

I do recall a theory that in the past the Earth was larger and the process of it getting smaller accounted for the uplift of mountains etc.

The opposite was also proposed – that the expansion of the earth created cracks in the surface and the continents drifted apart due to this expansion.

Both are sometimes called the “orange peel” Earth – for the fist imagine the orange drying out and the peel becoming rough as it contracts. For the second imagine the orange expanding and the peel tearing apart.

However these were both proposed prior to the understanding of plate tectonics. Maybe the encyclopaedia was suggesting something along these lines – is it a very old book?

Of course there are still some people, that like to dispute currently understood mechanisms for the development of the Earth, that still support these now redundant ideas, it could be that you have picked up a book by one of these crackpots.

I do recall a theory that in the past the Earth was larger and the process of it getting smaller accounted for the uplift of mountains etc.

The opposite was also proposed – that the expansion of the earth created cracks in the surface and the continents drifted apart due to this expansion.

Both are sometimes called the “orange peel” Earth – for the fist imagine the orange drying out and the peel becoming rough as it contracts. For the second imagine the orange expanding and the peel tearing apart.

However these were both proposed prior to the understanding of plate tectonics. Maybe the encyclopaedia was suggesting something along these lines – is it a very old book?

Of course there are still some people, that like to dispute currently understood mechanisms for the development of the Earth, that still support these now redundant ideas, it could be that you have picked up a book by one of these crackpots.

I don't think this is a "crackpot" idea, to me it makes perfect logical sense that an animal substantially larger than an elephant with current gravitation:
Will require massively thick skeleton.
Will not be able to move about freely.
Will have an overworked heart and other organs.

Changing the size of the earth to account for tectonic plates and orogeny, when there is a perfectly satisfactory theory that explains this, is a crackpot idea which is what I was pointing out in my previous post.

I don't think this is a "crackpot" idea, to me it makes perfect logical sense that an animal substantially larger than an elephant with current gravitation:
Will require massively thick skeleton.
Will not be able to move about freely.
Will have an overworked heart and other organs.

Did big dinos not have big bones?
Did big dinos move about freely/quickly or were they slow lumbering things?
Did big dinos not evolve organs that were able to cope with their great size (if not, then they would not have existed).

You don't need to change the size of the Earth to answer these questions!

Changing the size of the earth to account for dino morphology is also a crackpot idea (not that I said that it was in my previous post).