Although direct measurements of atmospheric carbon dioxide have only been taken consistently since the 1950s,?

Question

scientists have been able to retrieve data from the past 500,000 years. How have they been able to do this?

a. ice cores from ice sheets

b. sediment cores from the ocean

c. tree rings

d. all of the above

Answer 1

no one answered?  All of the above, although direct measurements come only from trapped atmospheric inclusions in ice. The other methods are indirect.  CO2 contents in the atmosphere have been reasonably (reasonably?) estimated well back into the paleozoic, and we have no ice or tree rings that are that old.

I presume that since the time frame of 500 k years is given, the answer is likely only (a), at least that seems to be the implied desired answer.  But the true answer is d.