What are three indirect ways a scientist can determine a past climate?

I already have Dendrochronology and another way is to study pollen... What's one more?



And a question off topic; what are the carbon dioxide levels during the day and during the night?



Please answers by 9:30 p.m. Pacific. Thanks!

What are three indirect ways a scientist can determine a past climate?
Just a few comments to add to the two excellent replies you have already been given.



On the link for finding past climate, one thing that was missing was the information left by humans. This include written records, paintings and drawings on paper, rocks, caves, etc.



Also, one must understand the changes that have taken place that may have caused by other natural changes. Example...for a brief cooling period over a large area may be explained by a major vocanic activity somewhere on the planet. This is usually short term, but a major eruption may skew the data for one to three years. A core sample will usually find a thin layer of ash for that period of time. And also, if you are looking at very long term changes. Remember, other things like the movement caused by plate techtonics may also be a factor. How the continent changes by movement or by sinking and rising may explain some of the results of the collected data.



Sometimes we fail to try to rule out other possible natural explanation for something we find in our data. That the nice thing about peer review.
Reply:That link in the first response covers most of it. There are also isotope ratios in sediments.



CO2 increases slightly at night because plants are metabolizing stored fuel instead of photosynthesizing, but the effect is tiny.
Reply:I can't type all of it, so here's the link:



http://www.niwascience.co.nz/ncc/faq/how...



I'll post the other answer if I can find it.



“Carbon dioxide is heavy. At night, it tends to settle in,” he says. “During the day we think the CO2 may just be rising with the warmer air. It could also be a function of vegetation. In most natural ecosystems the CO2’s going to be a lot lower during the day because the plants are taking in the gas for photosynthesis.”



I found the above from this link: http://chainreaction.asu.edu/ecology/dig...



Now, if I can actually answer your second question more specifically, I'll post that too...

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