Fossils are usually formed by filling gaps in biological tissues or wrapping the whole biological remains with minerals. Because these fossils preserve the morphology and structure of organisms, they are of great value to the study of paleontology and paleoecology.

The formation of solid fossils usually requires specific conditions and processes. First of all, biological remains need to be buried quickly to avoid being destroyed or rotted. Secondly, the buried remains need to undergo certain geological processes, such as mineral infiltration and metasomatism, before they can form fossils. Finally, these fossils need a long geological age and a suitable geological environment to be preserved and form the solid fossils we see.

There are many kinds of solid fossils, including but not limited to complete fossils, imprinted fossils, footprint fossils, cave fossils and so on. Among them, holographic fossil is the most common one, which preserves the complete form and structure of organisms and is of great significance to the study of the form and life habits of paleontology.

Entity fossils play an irreplaceable role in human understanding of the history of the earth and the evolution of life. Through the study of solid fossils, we can understand the information of paleontology such as morphology, living habits and ecological environment, and then infer the information of climate, geography and ecological system in the historical period of the earth. Therefore, solid fossils have important position and research value in geology, paleontology and ecology.

The formation of fossils need to meet the conditions:

1. Preservation of biological remains: Fossils need to preserve biological remains first, which usually requires a rapid burial mechanism, such as rapidly deposited sediments, freezing and volcanic eruption.

2. Mineral deposition: biological remains need to be filled or wrapped by minerals in order to form fossils in subsequent geological ages. This process is usually completed by mineral infiltration and metasomatism.

3. Suitable geological environment: Fossils need to experience specific geological environment, such as warm and dry climate and favorable geographical conditions for mineral deposition.

4. Long geological age: Fossils usually take a long geological age to form, so that biological remains and minerals have enough time to interact and stabilize.

5. Preservation conditions of biological tissues: The preservation conditions of biological tissues are very important for the formation of fossils. Only when the soft tissues of biological relics are rapidly updated or consolidated and the external environment remains relatively stable can high-quality solid fossils be formed.