- Fossils are the remains, traces or impressions of once living organisms.
- Fossils can take the form of skeletons, traces, coprolite, cast or impression.
- A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved. However, a fossil has no meaning without its context.
- Aging is important for constructing an evolutionary timeline.
- Distinct layers of sediment that accumulated on the earth’s surface.
- The study of strata and their relationships is called stratigraphy.
(“storage places”) These are fossil sites where there are numerous well preserved fossils.
A famous Lagerstatten from the Cambrian in Canada which has yielded many of the organisms that contribute to our understanding of the Cambrian explosion (rapid evolution of multicellular life, when nearly all major animal phyla appeared). Formed when an avalanche of mud carried animals into deep water (anaerobic conditions), resulting in exceptional preservation of soft tissue. (Reveals more than 20 additional arthropod designs other than the 4 described by taxonomists through the analysis of a million species)
Provides chronological estimates of the age of certain materials associated with fossils and direct age measurements of the fossil itself.
- Absolute dating of rocks, minerals and organic material using certain radioactive isotopes.
- Based on natural radioactive decay of certain elements such as potassium and carbon.
- Puts geologic events in chronological order without requiring that a specific numerical age is assigned to each event.
- Geologists have established a set of principles that can be applied to sedimentary and volcanic rock to determine the relative ages of geological events.
- Most of the history of geology and evolutionary biology is founded on relative dating.
geologic time scale
Was established by correlating layers based on index fossils.
The law of superposition assumes that in an undeformed sequence of sedimentary rocks, the bottom layer is the oldest and the upper layers get progressively younger.
This principle states that since each layer is deposited at the same time, even if erosion removes some of the layer, that layer is still the same layer after the gap. Even if there are gaps on the map, the layer is the same layer.
- The principle of original horizontality assumes that layers of strata are deposited mostly horizontally in bodies of water like oceans, or on the land on the margins of streams and rivers.
- Thus, any deformations of strata must have occurred after the rock was deposited.
- The movement of continental plates can reposition these layers from their original horizontality.
The principle of cross-cutting relationships states that fault movements that offset layers of rock must have occurred after the rocks they cut through.
- These are fossil species that are used to determine the relative ages of unknown fossils and correlate fossil sites across large discontinuous areas to identify strata.
- Index fossils are fossils that are common, easily identified, and found across a large area in a limited interval of time (distinct to a particular rock layer) and evolve quickly.
- Because they are uncommon, primate fossils aren’t good index fossils.
- Organisms like pigs and rodents are more typical index fossils as they evolve quickly, are more common, and are widely distributed.
- They’re used to construct stratigraphic correlation (alt alta ust uste denk getirmek) and identify layers in different places.
- 100-100,000 years
- Organic material such as bone, wood, charcoal, shells
- Radioactive decay of C14 that is removed from the atmosphere.
- Carbon has 3 isotopes. 12 and 13 are stable whereas 14 is unstable and thus radioactive. Because it is unstable, C14 often undergoes radioactive decay to become stable N14.
- Radioactive decay is the change in the number of protons and/or neutrons of an unstable isotope to become a stable isotope.
- The radioactive atoms in any mineral decay over time into stable daughter isotopes. The amount of time required for half of the parent isotopes to decay into stable daughter isotopes is called half-life.
- 10,000-4.6 billion
- Uranium bearing minerals
- Radioactive decay of uranium.
- 1,000-4.6 billion
- Potassium bearing minerals and glasses
- Radioactive decay of K40
- When potassium is incorporated into a mineral that forms when lava cools, there is no argon in the mineral as argon is a gas that escapes into the atmosphere while the lava is melted. Over time, potassium decays into argon at a steady rate, which accumulates in the mineral. As the rate of decay is known and stable, the amount of argon in the mineral can tell us when the lava was cooled and the age of the fossil preserved within.
Precambrian and Phanerozoic Eons
- Precambrian is before the Cambrian explosion and the emergence of multicellular life.
- Phanerozoic Eon begins 540 million years ago with the Cambrian explosion.
Eras within Phanerozoic
- Paleozoic (540 million years until 250 million years ago)
- Mesozoic (250 million years until 65 million years ago)
- Cenozoic (65 million years until now)
Periods within Paleozoic
- Ordovician (ordu)
- Silurian (slytherin)
- Devonian (dev)
- Carboniferous (karbon)
- Permian (permeable)
- COS diye Canlilar Patladi
Periods within Mesozoic
- Cretaceous (girit adasi)
- T-Rex jurassic park Canlisi
Periods within Cenozoic
- Genler son anda bulunuyor. Paleolithic neolithic ve quaternary protein.
This is the study of strata based on the principle of superposition, cross-cutting relationships and original horizontality.
- The principle of faunal succession states that different fossil species always appear and disappear in the same order, and that once a fossil species goes extinct, it can’t be found in younger rocks.
- Using overlapping age ranges, it’s possible to determine the relative ages of fossils.
Why aren’t there more fossils?
- Ordinary processes impede fossil formation. These processes include:
- Predators and scavengers may crush and disperse organic remains.
- Bacterial decay breaks down soft tissue.
- Dissolution in water may dissolve both soft and hard tissues.
- Physical disturbances such as wind action or water may destroy or displace remains.
What are the conditions that promote fossilization?
- Rapid burial allows for:
- Protection from physical disturbance (such quiet, deep water) and scavenging
- Anaerobic environments (protects from bacteria)
- This is why most fossils are found in sedimentary rock, but they can also be found in ash, peat, amber and permafrost.
Where are we likely to find fossils?
Sedimentary rocks formed by sedimentation at the bottom of a body of water. Ash, peat, amber, permafrost.
What typically gets preserved for animals?
Hard tissue such as teeth, bone, chitinous exoskeletons or calcium carbonate shells.
What gets preserved for plants?
Petrified wood, seeds, pollen, leaf impressions. Fossil flowers are rare due to the fragility of petals,
What gets preserved in microbes?
- They can be preserved in other organisms or stromatolites.
- Stromatolites are formed from biofilms of cyanobacteria that trap sediment which eventually hardens and forms sediments
What are original remains?
- This is a type of preservation where the skeletal or other body elements are present.
- This type of preservation is the most informative, as we can extract information regarding the organism’s morphology which helps us reconstruct its evolutionary history.
What is permineralization?
(petrification) is a type of preservation where minerals are deposited in tiny holes within bones, or wood and over time completely replace the original organism, leaving behind a stone structure.
What are trace fossils
- This is the preservation of the traces left by the organism.
- Pattern of root growth, movement in herds.
What are impression fossils?
Fossils made from a carbonaceous film imprint of the organism.
What are casts and molds?
A type of preservation where only the surface features of an organism’s morphology are revealed.
What are Steno’s principles of relative dating?
- Lateral continuity
- Original horizontality
- Cross cutting
When did the first life emerge on Earth?
3.7 billion years
End of Paleozoic
250 million years ago
end of mesozoic
65 million years ago
540 million years ago
when was earth formed?
4.6 billion years ago