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