In prehistoric times, when dinosaurs roamed the earth, and

[raccoon]

earlier, was the atmosphere significantly different? If a person could go back to those times, would they be able to breathe?

[shain from kane]

1. The stench! n/t

[RobertSeattle]

2. Adam and Eve survived.... :-)

But I think the answer, in general, the atmosphere would be fine for mammals back then.

http://observer.guardian.co.uk/uk_news/story/0,6903,1258655,00.html

[Poll_Blind]

3. Yes, it was different. Higher oxygen percentage in the air, IIRC.

Google around, though, I'm sure you can something a little less anecdotal.

A person would be able to breathe but depending on the level of oxygen, it might take a bit to acclimate to it.

PB

[flyingfysh]

8. higher oxygen levels permitted larger insects

Insects have an inefficient breathing system, so higher oxygen levels allow things like larger cockroaches.

[demnan]

4. Not enough polution

we would all die of the clean air without carbon emissions! ;)

[MisoWeaver]

6. There was plenty of Polution as well...

Well, there was. Vocanic emissions produce way more then anything else today as they did yesterday.

[RufusEarl]

5. I'm afraid we would OD on oxygen

[bananas]

7. U.S. astronauts used to breathe pure oxygen.

IIRC the Apollo missions and others.

[flyingfysh]

9. astronauts breathed pure oxygen at low pressure levels

Using ordinary atmospheric pressure for pure oxygen is not good. It was one of the mistakes made that killed the astronauts on Apollo 1. But only providing a single gas makes for simpler atmosphere systems in the spacecraft.

[spag68]

10. All this stuff is fake

There are no dinosaurs, the earth is 6000 years old.

[freethought]

11. Some good posts here, quite accurate.

During the dinosaur age and preceding it there were periods there the O2 levels were higher. This permitted insects,and arachnids to live on land and grow to some pretty frightening sizes. As I understanding there were spiders whose bodies were comparable in size to a human head and likely weighed a few pounds. How would you like to see that? A spider with a leg reach of 2 ft. across. Spiders freak me out a little. Dragonflies with 2-3ft. wing spans and who knows what else.
If a large animal like dinosaur could breath back then then it was likely that a human could breath as well.

[sakabatou]

12. Or centipedes the length of a compact?

[n2doc]

13. Oxygen has varied but air has been breathable for 1-2 billion years

(Hope this appears correctly) Right side scale shows % Oxygen in atmosphere. Today is about 21%...


Yale Researchers Attribute Ancient High Levels Of Oxygen In The Atmosphere To The Rise Of Trees And Large Plants
New Haven, Conn.. -- A new method of calculating oxygen in the Earth's atmosphere suggests that an increase more than 300 million years ago was caused by the rise and spread of trees and other vascular land plants, a Yale study finds.

The new plant life produced dead organic matter resistant to decomposition by bacteria that was buried in sediments, and, as a result, extra oxygen was added to the atmosphere by increased global photosynthesis, according to Robert A. Berner, the Alan M. Bateman Professor of Geology and Geophysics at Yale.
"The rise of large vascular land plants had a significant effect on atmospheric composition, both oxygen and carbon dioxide," said Berner.
The higher concentrations of oxygen lasted for 100 million years and were significantly higher than the Earth's current oxygen content of 21 percent. Published in the March 3 issue of Science, the study shows that the calculated high oxygen levels during this period verify earlier independent estimates and that this high oxygen may have been an important factor in affecting the evolution of giant insects.
The study's theoretical calculations rest partly on experimental work on land plant growth at the University of Sheffield in England by David Beerling and his associates and on marine plankton growth at the University of Hawaii by a team led by Edward Laws and Brian Popp.
"As a result of these experiments, we were better able to calculate realistic changes in atmospheric oxygen over geologic time," Berner said.
In addition to Berner, Beerling, Laws and Popp, the study's team included former Yale graduate student, Steven T. Petsch, and J. A. Lake, W.P. Quick, and F.I. Woodward from the University of Sheffield in England; and R.S. Lane, M.B. Westley and N. Cassar from the University of Hawaii.

http://www.sciencedaily.com/releases/2000/03/000308081611.htm

[Odin2005]

14. There is a good book that just came out on just this subject!

The book is called "Out of Thin Air" and is by paleontologist Peter Ward, I'm currently reading it right now.

The Earth originally had no free oxygen in the air or oceans. Around 3.4 billion years ago oxygen-producing photosynthesis evolved, but it took untill 2.1 billion years ago for all the iron in the ocean to be turned into rust (that rust, as it turns out, is the iron ore we mine today), allwong free oxygen to accumulate. It wasn't untill around 800 million years ago that oxygen levels hit 15% for the first time.

From the late Precambrian to the late Silurian oxygen levels fluctuated around 15%. The spread of the first land plants in the Silurian and Devonian sent oxygen levels soearing to 25%. During the Late Devonian mass extinction oxygern levels crashed to under 15%, then started to increae again. During the Carboniferous period the oxygen levels soared over 30%, peaking at 35% in the Early Permian. During the Permian mass extinction, the worst mass extinction in Earth's history, was associated with the most massive crash in oxygen levels in Earth's history, dropping drom 30% to under 15% in only a few million years.

During the Triassic the oxygen levels began to rise again, reaching 18% in the middle of the period, but then crached to 12%, the lowest oxygen levels since the Precambrian. The Oxygen levels stayed below 15% throughout the Jurassic. During the Cretaceous the Oxygen levels started to increase, and has been increasing since.