Sediments from Lakes Beds and Seafloors The climate history preserved within layers of sediments that slowly accumulate on the bottoms of lakes and oceans can span hundreds of millions of years or longer.
Sequences of sediments that are currently at the bottom of lakes or on the ocean floor are used to interpret climates of the recent past (see map).
Rocks preserved on the continents that are thousands, millions, hundreds of millions, or even billions of years old are used to interpret the much more distant past.
Proxy records with overlapping timeframes can be correlated to build up a chronology that spans a longer time period than does any individual piece of data.
For example, by combining tree ring data from a tree that sprouted in the 1850s and was recently cut down with the ring pattern in a beam from a log cabin built in the 1870s, we might establish a proxy climate chronology that runs from the 1700s to the present day.
Various types of paleoclimate proxies are used to understand past climate.
Proxies span different periods of prehistory, provide different degrees of precision, and record different aspects of climactic conditions (temperature, precipitation, etc.) from one another.
These items fall to the water surface and sink to the bottom.
Skeletal materials from organisms and algae living within the water also 'rain' down to the bottom, particularly in deep-ocean environments.
The long cores are cut into shorter segments and split lengthwise down the middle.