Paleoecology

Paleoecology (also spelled palaeoecology) is the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales. As a discipline, paleoecology interacts with, depends on and informs a variety of fields including paleontology, ecology, climatology and biology.
Paleoecology emerged from the field of paleontology in the 1950s, though paleontologists have conducted paleoecological studies since the creation of paleontology in the 1700s and 1800s. Combining the investigative approach of searching for fossils with the theoretical approach of Charles Darwin and Alexander von Humboldt, paleoecology began as paleontologists began examining both the ancient organisms they discovered and the reconstructed environments in which they lived. Visual depictions of past marine and terrestrial communities have been considered an early form of paleoecology.
Major principles.
While the functions and relationships of fossil organisms may not be observed directly (as in ecology), scientists can describe and analyze both individuals and communities over time. To do so, paleoecologists make the following assumptions:
Paleoecological methods.
The aim of paleoecology is to build the most detailed model possible of the life environment of previously living organisms found today as fossils. The process of reconstructing past environments requires the use of "archives" (e.g., sediment sequences), "proxies" (e.g., the micro or mega-fossils and other sediment characteristics that provide the evidence of the biota and the physical environment), and "chronology" (e.g., obtaining absolute (or relative) dating of events in the archive). Such reconstruction takes into consideration complex interactions among environmental factors such as temperatures, food supplies, and degree of solar illumination. Often much of this information is lost or distorted by the fossilization process or diagenesis of the enclosing sediments, making interpretation difficult.
Some other proxies for reconstructing past environments include charcoal and pollen, which synthesize fire and vegetation data, respectively. Both of these alternates can be found in lakes and peat settings, and can provide moderate to high resolution information. These are well studied methods often utilized in the paleoecological field. 
The environmental complexity factor is normally tackled through statistical analysis of the available numerical data (quantitative paleontology or paleostatistics), while the study of post-mortem processes is known as the field of taphonomy.
Quaternary.
Because the Quaternary period is well represented in geographically extensive and high temporal-resolution records, many hypotheses arising from ecological studies of modern environments can be tested at the millennial scale using paleoecological data. In addition, such studies provide historical (pre-industrialization) baselines of species composition and disturbance regimes for ecosystem restoration, or provide examples for understanding the dynamics of ecosystem change through periods of large climate changes. Paleoecological studies are used to inform conservation, management and restoration efforts. In particular, fire-focused paleoecology is an informative field of study to land managers seeking to restore ecosystem fire regimes.