Simulate fossilisation over geological time · Adjust burial & environment conditions · Track preservation index
This interactive model traces an organism's journey from death to fossil across up to 65 million years, animating the key stages of taphonomy. Organic mass decays following first-order kinetics, m = 100·e−kt, where the rate k responds to temperature, oxygen and pH, while rapid burial shields the remains. Sediment compacts, mineral-rich groundwater progressively fills the void, and a composite preservation index rewards quick anoxic burial, neutral pH and thorough mineralisation.
A cross-section of decay, burial and mineral replacement. Organic mass follows exponential decay e−kt with k scaled by temperature, oxygen and pH; burial depth grows with the burial rate and a compaction factor; mineral fill rises with depth, time and near-neutral pH; and a weighted preservation index combines burial speed, anoxia, pH and mineralisation.
Pick a preset (Marine Sediment, Amber, Desert or Peat Bog), or adjust four sliders: Burial Rate (0.1–20 mm/yr), Oxygen Level (0–100%), pH (4–10) and Temperature (0–60°C). Drag the Time slider (0–65 Ma) or press Play to animate, and watch the live stats for stage, preservation index, depth, organic mass and mineral fill.
Less than one species in a thousand is thought to leave any fossil record at all. Soft tissues almost always rot before burial, so most fossils are hard parts like bone, shell or wood, often turned to stone when minerals such as silica or calcite replace the original material molecule by molecule.
Taphonomy is the study of everything that happens to an organism between death and discovery as a fossil: decay, scavenging, transport, burial and chemical alteration. It matters because only a tiny fraction of organisms survive these processes, so the fossil record is heavily biased toward hard-bodied creatures that were buried quickly in the right conditions.
It tracks organic mass using exponential decay, m = 100·e−kt, where the decay coefficient k rises with temperature and oxygen and falls away from neutral pH. A weighted preservation index then combines rapid burial, low oxygen (anoxia), near-neutral pH and the degree of mineral fill. High scores require the remains to be buried and mineralised faster than they can rot.
Burial Rate (millimetres per year) controls how fast sediment accumulates and protects the body; Oxygen Level sets how oxic or anoxic the setting is, with anoxic conditions slowing decay; pH affects both decay rate and mineralisation, which works best near neutral; and Temperature scales the decay rate, with warmer water or soil speeding breakdown. The presets bundle realistic combinations for marine, amber, desert and peat-bog settings.
It is an educational simplification rather than a research tool. The exponential decay law, the protective effect of fast anoxic burial and the role of mineral replacement are all genuine principles, but real taphonomy also involves microbial activity, sediment chemistry, pressure and luck. Treat the numbers as illustrative trends rather than precise predictions.
Oxygen feeds the bacteria and scavengers that destroy a carcass, so an oxygen-poor, quickly buried setting halts decomposition before the body falls apart. This is why exceptional fossil sites, known as Lagerstaetten, often form in anoxic lake beds, lagoons or mud, where even delicate soft tissues can occasionally be preserved.
Fossilization—the process by which organic remains are preserved in rock—is extraordinarily rare. Of the vast numbers of organisms that have ever lived, only a tiny fraction become fossils, and fewer still are discovered and described. The scientific study of fossilization processes is called taphonomy. For fossilization to occur, an organism must be buried rapidly enough to avoid scavenging and decay, usually by sediment in water-rich environments such as river deltas, lake bottoms, seafloors, and tidal flats.
The most common fossilization mode is permineralization: after burial, groundwater percolates through porous bone or wood and deposits minerals (calcite, silica, pyrite) in the pore spaces, gradually replacing or infilling the original organic tissue with rock-hard mineral replicas. Replacement fossilization occurs when the original material dissolves and is replaced molecule by molecule by new minerals. Compression leaves carbonized films of soft tissue; amber entombment preserves insects and plant material in exquisite detail by embedding them in hardened tree resin.
This simulator models the stochastic process of organism death, burial, diagenesis (rock formation under heat and pressure), and eventual erosion to the surface. You can adjust burial rate, sediment type, water chemistry, and geological time to observe how these factors control the probability and quality of preservation—illustrating why certain environments and time periods are overrepresented in the fossil record.
Why are hard parts (bones, shells) more commonly fossilized than soft tissue?
Hard parts composed of calcium phosphate (bone, teeth) or calcium carbonate (shells) are chemically resistant and structurally rigid, resisting decay long enough for mineral replacement to occur. Soft tissue (muscle, skin, organs) decomposes within days to weeks from bacterial activity and autolytic enzymes unless burial is exceptionally rapid or conditions inhibit decay (anoxic water, cold, rapid mineral entombment). Exceptional soft-tissue preservation occurs in the Burgess Shale (rapid burial in anoxic mud), Liaoning (early Cretaceous lake sediments), and insects in amber.
What is permineralization and how does it work?
Permineralization occurs when groundwater saturated with dissolved minerals percolates through buried porous tissue (bone, wood). The minerals precipitate in pore spaces, creating stone-hard internal casts while preserving external structure. Over millions of years, the original organic molecules may be partially or entirely replaced by minerals—calcite, silica, pyrite, or iron oxides. Petrified wood in the Petrified Forest National Park was permineralized by silica-rich groundwater, preserving cell-level detail while turning wood to stone.
How old can fossils be, and what is the oldest known?
The fossil record extends to approximately 3.5 billion years ago, with microbial stromatolites (layered mats formed by photosynthetic cyanobacteria) representing some of the oldest definitive fossils. Chemical biomarkers (molecular fossils) suggest life existed even earlier, ~3.8 billion years ago. Macroscopic multicellular organisms appear in the Ediacaran (635–541 million years ago), and the Cambrian Explosion (~541 million years ago) produced the body plans of most modern animal phyla. Older fossils are rarer because ancient rocks have been repeatedly metamorphosed.
The fossil record is biased by preservational factors. Environments producing fine-grained sediment (deep ocean, calm lakes, river deltas) preserve organisms better than high-energy environments (riverbeds, beaches) where remains are destroyed by transport. Species living in upland or terrestrial environments leave far fewer fossils than aquatic ones. Subsequent erosion, metamorphism, and subduction destroy old sedimentary rocks. The Signor-Lipps effect means that even if a species goes extinct suddenly, its last fossil occurrence will appear earlier in the record due to incomplete sampling.
Radiometric dating measures the decay of radioactive isotopes in rocks or minerals surrounding a fossil. Uranium-lead dating (half-life 4.5 billion years) dates ancient igneous rocks; potassium-argon dating (half-life 1.25 billion years) dates volcanic ash layers intercalated with fossil-bearing sediments. Carbon-14 dating (half-life 5,730 years) applies only to organic material younger than ~50,000 years. By bracketing fossil layers between dateable volcanic strata above and below, geologists constrain fossil ages to within a few percent.