Fossils-types of fossils and fossilization
- 1. FOSSILS, TYPES OF FOSSILS AND FOSSILIZATION PG DEPARTMENT OF LIFE SCIENCES RAYAGADA AUTONOMOUS COLEGE, RAYAGADA
- 2. What Is a Fossil? Definition • A fossil is the preserved remains, impression, or trace of any once- living organism from a past geological age. These include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants. What Is Not a Fossil Not everything that looks like a fossil is one: •Pseudo-fossils: These are patterns in rocks that look like fossils but are not. •Rocks with Unusual Shapes: Natural rock formations may resemble fossilized remains. •Man-Made Artifacts: Objects like stone tools or pottery fragments are sometimes mistaken for fossils.
- 4. Age Range of Fossils • Fossils range in age from a few thousand to several billion years old. Stromatolites are among the oldest fossils, dating back perhaps are long ago as 4 billion years. The most recent fossils come from the last Ice Age, as recently as around 12,000 years ago. • Archean Eon (4.0 to 2.5 billion years ago) • Stromatolites: These are layered bio-chemical accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by microorganisms, primarily cyanobacteria. They are among the oldest known fossils, dating back more than 3 billion years. • Proterozoic Eon (2.5 billion to 541 million years ago) • Acritarchs: A group of microfossils (30 to 1800 micrometers) which are likely the remains of the cysts of ancient eukaryotic algae from as far back as 1.8 billion years ago. • Banded Iron Formations (BIFs): These are distinctive units of sedimentary rock that are almost always of Precambrian age, some dating to 2.5 billion years ago. They consist of repeated thin layers of iron oxides, either magnetite or hematite, alternating with bands of iron-poor shale and chert. The formation of BIFs links to the activity of the earliest life forms, specifically cyanobacteria.
- 5. • Phanerozoic Eon (541 million years ago to present) • Cambrian Period (541 to 485 million years ago): This period marks the point when most of the major groups of animals first appear in the fossil record. Examples include the well-known Burgess Shale fauna, with creatures like Anomalocaris and trilobites. • Ordovician Period (485 to 444 million years ago): Characterized by diverse marine fauna such as the early cephalopods (nautiloids), corals, and trilobites. • Silurian Period (444 to 419 million years ago): Known for the first fossil records of land plants and jawed fishes. Age Range of Fossils
- 7. How a Fossil Forms • Fossilization is complex process that typically occurs in sedimentary rocks. It’s also rare. Most organisms die and decompose, never becoming fossils. The process involves: • 1. Death of an Organism • Description: The process begins with the death of an organism. The chances of fossilization are higher if the organism has hard parts such as bones, shells, or teeth. • 2. Decomposition and Burial • Description: Rapid burial is crucial for fossilization. This sometimes happens through natural events such as floods, volcanic ashfall, or landslides. The quicker an organism is buried, the less it decomposes and the more likely it is to fossilize. Soft tissues decompose quickly (days to weeks), whereas hard parts like bones last longer (hundreds to thousands of years) if not exposed. • 3. Sediment Accumulation • Description: Layers of sediment build up over the remains. The weight of these layers compacts the sediment, and the minerals in the water start seeping into the remains. This process can take a very long time, depending on sedimentation rates and the depth of burial.
- 8. 4. Mineralization and Petrification • Description: This is the key phase of fossilization, known as permineralization or petrification. Minerals dissolved in groundwater slowly replace the organic materials, or fill in the spaces within the organism’s remains. This process takes thousands to millions of years. For instance, petrification of wood might take a few thousand years, while the mineralization of bones could span millions of years. 5. Erosion and Exposure • Description: Erosion eventually exposes the fossilized remains at the Earth’s surface. This can happen due to natural geological processes like wind or water erosion. The timeframe for this step is highly variable and depends on geological and environmental factors.
- 11. TYPES of FOSSILS: 1. Body Fossils (Preserved Remains) • Body fossils are direct remains of the organism itself. • Bones and Teeth: Most common in vertebrates like dinosaurs, mammals, fish, and birds. Example: Tyrannosaurus rex skeleton. • Shells and Exoskeletons: Common in invertebrates like mollusks and trilobites. Example: Ammonite shells. • Leaves and Wood: Plant fossils, including petrified wood where the organic material has been replaced with minerals. Example: Fossilized leaves of Ginkgo biloba. • Hair, Skin, and Feathers: Rare due to their delicate nature, but incredibly valuable for understanding soft-tissue anatomy. Example: Feathered dinosaurs.
- 12. 2. Trace Fossils • Trace fossils, or ichnofossils, are indirect evidence of an organism’s presence. • Footprints and Tracks: Impressions left by animals. Example: Dinosaur footprints in sedimentary rocks. • Burrows and Borings: Holes or tunnels in sediments or wood, indicating the activity of an organism. Example: Trace burrows made by ancient marine worms. • Coprolites: Fossilized feces, providing insight into the diet and digestive system of organisms. Example: Dinosaur coprolites. • Gastroliths: Stones swallowed by animals, often polished smooth inside the gastrointestinal system, and then fossilized. Example: Gastroliths found near dinosaur remains.
- 13. 3. Molecular Fossils Molecular fossils, or biomarkers, are organic molecules that provide chemical evidence of past life. Lipids and Pigments: Organic molecules that can survive long after the organism’s death. Example: Chlorophyll derivatives in ancient plant remains. DNA Residues: Rare and typically only found in exceptionally preserved specimens. Example: DNA fragments in amber-preserved insects.
- 14. • 4. Microfossils • These are tiny fossils, often of single-celled organisms, requiring magnification to be seen. • Foraminifera and Diatoms: Single-celled organisms with hard parts that fossilize well. Example: Foraminifera in marine sedimentary rocks. • Pollen and Spores: Microscopic plant structures that can be preserved in sediment. Example: Pollen grains in peat bogs or lake sediments.
- 15. Amber Fossils: • Amber fossils are formed when organisms become trapped in tree resin, which later hardens into amber. Inclusions within amber can preserve various organisms, including insects, pollen, seeds, and small animals.
- 16. Determination of Age of Fossils… • Relative Dating: Relative dating involves determining the age of fossils in relation to other fossils or rock layers. This method relies on the principles of stratigraphy, which states that older layers of sedimentary rock are found beneath younger layers. By examining the position of fossils within rock layers and their relationship to other fossils, paleontologists can estimate their relative ages. • Biostratigraphy: Biostratigraphy is a form of relative dating that utilizes the known age ranges of fossil species to estimate the age of a particular fossil assemblage. By correlating the presence of certain index fossils with specific time periods, scientists can assign relative ages to the fossils found in a particular rock layer. • Radiometric Dating: Radiometric dating is a method used to determine the absolute age of fossils and rocks by measuring the decay of radioactive isotopes. This technique relies on the principle that certain isotopes decay at a predictable rate over time. By measuring the ratio of parent isotopes to daughter isotopes in a sample, scientists can calculate the age of the fossil or rock. • Carbon-14 dating is commonly used to date organic remains up to approximately 50,000 years old. It relies on the decay of the radioactive isotope carbon-14, which is present in living organisms but decays after death. • Potassium-argon dating and argon-argon dating are commonly used for dating volcanic rocks and minerals, as they rely on the decay of potassium-40 to argon-40. This method is useful for dating rocks older than a few thousand years. • Uranium-lead dating and other methods based on the decay of isotopes like uranium, thorium, and rubidium are used to date older rocks and minerals, potentially reaching back billions of years.
- 17. Uses of Fossils Fossils have uses by geologists, biologists, and other scientists: • Studying Evolution: Tracing the development and changes in species over time. • Understanding Ancient Environments: Offering clues about past climates and ecosystems. • Dating Rocks: Using radioactive elements within fossils for radiometric dating. • Educational and Recreational: In museums and as collectibles. https://biologynotesonline.com/fossils-definition-types-formation-dating-examples/