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Revision as of 06:50, 9 August 2001 by Arco Scheepen (talk | contribs) (Fixed link)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)Fossils are the mineralized remains of animals or plants. Fossilization is a rare occurrence, because natural materials tend to be recycled. In order for an organism to be fossilized, the remains need to be covered by sediment as soon as possible. There are different types of fossils, and fossilization processes:
Permineralization'
This process consists of literally turning an organism into stone. The organism gets covered by sediment soon after death, or after the initial decaying process. The degree in which the remains are decayed when covered, determines the later details of the fossil. Some fossils only consist of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. Once covered with sediment, these layers slowly compact to rock, after which the chemicals in the remains are slowly replaced with hard minerals.
Mould, cast and trace fossils
If percolating water dissolves the remains of an organism, and thereby leaves a hole, this is called a mould fossil. If this hole is filled with more minerals, it is called a cast fossil. If the burial of the organism was rapid, than chances are that even impressions of soft tissues remain. Trace fossils are the remains of track ways, burrows, footprints, eggs and shells, nests and droppings. The latter, called coprolites can give insight in the feeding behavior of animals, and can therefore be of great importance.
Resin fossils
Smaller animals, insects, spiders and small lizards, can be trapped in resin, which oozes from trees. These fossils, on which whole movies can be based (Jurassic Park), can be found in sand- or mudstones.
Pseudofossils
These are regular patterns in rocks, which are produced by natural occurring processes. They can easily be mistaken for real fossils. These fossils can be formed by naturally formed fissures in the rock that get filled up by percolating minerals. Other types of pseudofossils are kidney ore, round shapes in iron ore, and 'moss agates', which look like plant leaves.
Living fossils A term used for a living species, which was thought to be extinct, or not resembling any other living species. Examples of living fossils are the coelacanth (Latimeria chalumnae), nut clams (Ennucula superba), Lingula anatina, an inarticulate brachiopod, and the horseshoe crab (Limulus polyphemus).
Fossils and the geological timescale
- Precambrian (3.8 billion to 570 million years ago)
- Bacteria and blue-green algae
- Cambrian (570 to 500 million years ago)
- First invertebrates
- Ordovician (500 to 440 million years ago)
- First trilobites
- Silurian (440 to 410 million years ago)
- First land plants
- First land invertebrates
- First jawless fish
- Devonian (410 to 365 years ago)
- First ferns and seed plants
- First insects
- First amphibians
- Carboniferous (365 to 290 million years ago)
- First flying insects
- First reptiles
- Permian (290 to 245 million years ago)
- Triassic (245 to 210 million years ago)
- Extinction of trilobites
- First dinosaurs
- First mammals
- Jurassic (210 to 140 million years ago)
- First birds
- Cretaceous (140 to 65 million years ago)
- Paleocene (65 to 55 million years ago)
- Diversification and spreading of mammals
- Eocene (55 to 38 million years ago)
- Oligocene (38 to 25 million years ago)
- First grasses
- Miocene (25 to 5 million years ago)
- Pliocene (5 to 2 million years ago)
- First hominids
The study of fossils is called Paleontology.