You can see changes just by looking at the colour, but by looking at the different isotopes of oxygen in the core you can estimate how much ice was around. They measure the 16-oxygen and 18-oxygen (18-oxygen has 2 more neutrons) in the core.
Most evaporation happens where it's warm in the tropics, and the lighter 16-O is evaporated more easily. When it rains, the remaining 18-O rains out more easily because it's heavier. By the time the vapour and clouds get nearer the pole where the ice sheets are, they have lost almost all their 18-O and they're mostly made up of 16-O. This falls as snow and gets trapped in the ice.
This means that the ice has mostly 16-O, and if it's cold and there's lots of ice, then the oceans end up seeing a lower proportion of 16-O and a higher proportion of 18-O, because they've lost some 16-O to the ice. The animals and things that live in the ocean absorb more 18-O and when they die and fall to the bottom they eventually form sedimentary rocks.
When we dig up these rocks we measure the ratio of 18-O to 16-O, and if there's lots of 18-O then we know that there was lots of ice at the time so it was colder.
There's a bit of an explanation on the fifth slide here:
http://www.colorado.edu/geography/class_...
Rocks
Permian sandstone, coloured red with iron oxides, indicating a hot climate at the time of deposition (Gateford sand pit) Permian sandstone, coloured red with iron oxides, indicating a hot climate at the time of deposition (Gateford sand pit).
Glacial till made of sand, gravel and rock carried by the ice at West Tarbert Glacial till made of sand, gravel and rock carried by the ice at West Tarbert.
The characteristics of different rocks depend on the environment in which the sediments were deposited.
Some sands and gravels are dropped by glaciers as they melt and they become a distinctive rock called till.
Where till is found there must have been glaciers and therefore it must have been cold.
Rocks that form in a hot desert environment are often coloured red with iron deposits.
Also at high temperatures, sea water can evaporate quickly leaving behind a layer of salt on the ground which becomes preserved in the rocks and is another indicator of a hot climate.
There are a couple of good answers, but there is an even simpler one that hasn't been mentioned. Even without fossils, sedimentary rocks tell you something about what the environment was like when they were formed. They may tell you that ocean existed where it doesn't now, or whether the climate was wetter or drier (you might have mudstones in the first case and evaporites in the second), or you might even find evidence of past sand dunes.
Of course, you always have to determine whether the rocks are in their original location and assign some sort of date to them.
In my geology classes, we learned that certain ice is considered a mineral but glaciers aren't and they aren't sedimentary rocks. Doing isotopic analyses on glaciers isn't an answer. It seems to me that if you throw some numbers around and are a good snake oil salesman you are likely to sell a few bottles of snake oil among alarmists. If you gave MTR a thumbs up, I hope you enjoy your snake oil.
It is really pretty simple. There are numerous answers but the most obvious to me is that sedimentary rocks typically have fossils which will show different species adapted to different climates. As sediments accumulate, the upper sediments are newer and if you have species adapted to warmer climates in upper sediments, you can assume that the climate changed.
isotope analysis
