Fossil Records Rafa, Bengi, Kat, Sam, Max
How are fossils formed? • - luck and preservation • - most living things are usually recycled upon death • Freezing (refrigeration) • best means of preservation of ancient materials. rare. animal must be continually frozen from time of death until discovery. limits possibilities to animals from the last ice age. • Drying (desiccation) • usually found in arid parts of the world. soft tissues (including skin and organs) are preserved for thousands of years if completely dried.
Asphalt • excellent preservative, formed by crude oil seeping through fissures in the earth. bones, teeth, shells, the exoskeletons of insects and even some plant seeds have been found this way • Amber • insects, spiders and small lizards may be perfectly preserved if engulfed in tree sap, which then hardens into amber • Carbonisation (distillation) • Living things decompose but leave behind only their carbon, which creates an impression in the rock • Permineralization • most common method of fossil preservation. minerals fill cellular spaces and crystallize. shape of original plant or animal is preserved as rock. sometimes, none of the organic material remains - only rock.
What things are preserved as fossils? • The only parts of deceased organisms that are left behind are the parts that were mineralized during life (bones, teeth for vertebrates, exoskeletons of invertebrates) • Index fossils - Remains of organisms that help define a geological period • Trace fossils - Remains of track ways, burrows, bioerosion, eggs and eggshells, nests, droppings and other types of impressions (including fossilized poo) • Transitional fossils - any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group • Microfossils - Tiny fossils
Resin Fossils - a natural polymer found in many types of strata throughout the world, even the Arctic (small invertebrates likes bugs and spiders, and sometimes lizards and other small vertebrates) • Derived Fossils - a fossil found in rock made significantly later than when the fossilized animal or plant died • Fossil Wood - Remains of trees. • Mistaken for fossils: • Pseudofossils- rocks that show geological patterns • Living fossils - fossils of things that haven't evolved
Where and when were the oldest fossils found? • -One of the biggest challenges for geologists is deciding when a fossil is really a fossil, particularly when it comes to early life *No bones to analyze *Mineralized spheres representing simple cells and filaments could just be crystals or other irregularities in the sediment • Martin Brasier and David Wacey claim they have discovered 3.4 billion year old cells, possibly the oldest ever found • Other microorganisms that are as old or older have been reported but many question the validity of those fossils • Chemical analyses of the minerals near the cells suggest the microorganisms depended on sulfur for fuel
Brasier first suspected the ancient rock formation would be a good place to look because it resembled a modern beach which indicated that the sediments had not been badly heated or distorted since they were laid down *Analyses show that the beach is about 3.4 billion years old • Fossils: hollow, some clustered together in groups surrounding what looked like a membrane *The cell walls contained a different isotope (version of carbon) from the surrounding rock *They also found tiny mineral crystals containing a different version of sulfur in and around the cells- evidence that the microorganisms were processing sulfur from the environment to extract energy • Early on, oceans were really steamy, oxygen was lacking --> supports the idea that life depended on sulfur-containing compounds
How do you measure how old fossils are? • Radiocarbon dating • Date ancient fossils • Carbon is present in all living things • Although the majority of carbon taken in is not radioactive, a small amount of radioactive carbon is taken into all living bodies • Carbon will decay when bodies decompose • Radioactive carbon decays at a known rate, science can look at the amount of decay in a fossils radioactive carbon and determine a relative date • However, scientists do not carbon date the actual body/fossil - they carbon date the rock that the fossil was found in
Why are fossils important evidence to evolution? • - Fossils give a record as to what organisms lived throughout different time periods (lower layer shows the oldest fossils) • - The radioactive carbon dating is used in dating how old a fossil is by finding the amount of carbon^14, and then calculating how many half lives have passed to teach this amount • - See very simple organisms at first and then new, more complex organisms appearing over time. • - They show the changing representations of species over time from simples organisms to more complex in a development that reflects an evolutionary progression • - They show how creates changed over vast periods of times and adapted to various environments • - Find a succession of organism that suggest a history of incremental development from one species to another • - Using fossils, scientists and reconstruct body types of animals that no longer exist and put together a "Tree of Life" to describe the evolutionary relationship between organisms