Quest 1 - Finding Fossils

Fossil

• “Something dug up"

• Remains, impressions, or evidence of once living organisms preserved through time in sedimentary rock/tree resins

Ancient

About 10,000 years old

Fossil Record

Total collection of fossils that’ve been found around the world

Formation (extremely rare)

1. Organism dies

2. Gets buried in the right sediment & quickly

3. Slow decay

4. Sediments accumulate & harden

Ideal conditions for formation

Rapid burial, slow decomposition

Intact fossils

Decomposition doesn’t occur & organic remains are preserved

Compression fossils

Sediments accumulate on top of material & compress it into thin carbonaceous film

Permineralization (most common)

Remains decompose slowly & dissolved minerals infiltrate cell’s interiors & harden into stone; contain some organic components/structure

Replacement

Replaces organic components with minerals

Internal mold (steinkern)

Sediment fills inside of species, hardens, & is left after (snail shell) dissolves

External mold (impression)

Sediment surrounds a species & hardens, then leaves a mold of the outside, even if long decayed/dissolved

Casts

Remains decompose after burial & dissolved minerals create a cast in remaining hole

Trace fossils

Not part of organism; sedimentation & mineralization preserve indirect evidence

• Tracks

• Trails

• Fossilized poop

High quality fossilization/preservation

Burgess Shale- mud preserved marine life

Messel Shale- toxic gases suffocated animals

Ulrich Quarries- fish carcasses in mud/calcareous shale

Freezing & drying

If greater than 10,000 years old & are remains of ancient life, then it can be a fossil

Taxonomic & tissue bias

Some organisms are more likely to decay slowly

• Bones & shells

• Tissues w/ a tough outer coat

Habitat bias

Organisms that live where sediment is actively being deposited

• Beaches & swamps

• Burrowing organisms more likely to fossilize

Temporal bias

Most recent fossils are more common than ancient ones

Abundance bias

Organisms that are abundant, widespread, & present for a long time leave more evidence

Importance of fossils

• Direct evidence of extinct organisms (ex. transitional species)

• Where they lived/what they looked like

• Past environmental conditions

• Age of extant organisms & their ancestors

• Evidence of evolution

How to figure out age

Cannot know exactly; look up site info:

• Which formation

• Websites

• Regional guides

• State geological surveys

Relative dating

Can determine if fossil is relatively older/younger based on layer it’s found in

Sediment

Solid material moved & deposited to a new location

• Pieces of rock

• Minerals

• Organic material (remains of plants/animals)

Sedimentary rock

Accumulated sediment that hardens (lithifies) into rock

• Shale

• Coal

• Siltstone

• Sandstone

• Limestone

Strata

Horizontal layers of sedimentary rock

Principles of Original Horizontality & Superposition

Sediment laid down horizontally (or nearly so); happens in

• Oceans

• Lakes

• Near rivers

• Younger rock layers above older ones (undeformed sequence)

Principle of Cross-cutting Relationships

Any geologic features that cut across strata must’ve formed after the rocks they cut through

Principle of Faunal Succession (PFS)

Different fossil species always appear & disappear in same order (extinct at one point, doesn’t reappear later)

Index fossils

Species used to distinguish one layer from another

• Limited time interval

• Typically common, widespread, & easy to ID

• Strata in different areas that same index is found in were likely deposited at same time

• Unknown fossils found in same strata as index can tell you age of unknown one

• Index’s above/below unknown fossil can let you know if younger/older relatively

Numerical/Absolute dating

Estimates are made for a rock/fossil in number of years

• Radioactive elements decay to a non-radioactive form in a known amount of time

• Amount of element left provides age

Radiometric (isotopic) dating

• Based on formation of one isotope

• Radioactive isotopes have unstable nuclei

• Parent isotope undergoes radioactive decay & results in a stable daughter isotope

Decay rate

Constant for a radioactive isotope; can be used to estimate age

Half-life

Time required for the decay of ½ of a given amount of unstable parent

Radiocarbon

Determine the age of more recent things (1-70,000 years)

Potassium-Argon

Much older things (billions of years ago)

Plato

Essentialism- species have an immutable (unchanging) perfect essence; variation is considered “accidental imperfection”

Aristotle

Ordered organisms into a “linear chain of being”

• Species are immutable

• Species are ordered by increasing size & complexity

• Sequence started w/ minerals & lower plants

• Humans on top

Special creation

Each species was created individually by God in the same form it is today

1. Species are independent (unrelated)

2. Life on Earth is young (~6,000 years old)

3. Species are immutable

• Christianity & essentialism

• Species designed for their environment

Linnaeus (18th century)

Developed a framework for modern classification (in “Systema Naturae”)

• Reveal plan of creation?

• Appreciate God’s wisdom?

Hutton & Lyell (18th century geologists)

Uniformitarianism- geological processes today were similar to past ones

Gradualism- small forces working slowly over time could result in large geological changes

• Grand Canyon

Lamarck (18th century)

• Suggested species rose by natural causes

• Each originated individually by spontaneous generation from non-living matter

• Species differ bc they have different needs (Giraffe’s neck)

• Inheritance of acquired characteristics

Evolution

Descent with modification

Fossil Record & evolution

Simple to complex; traits & species gradually changing

• Microfossils (diatoms)

• Horses

• Whales

• Archaeopteryx

• Tiktaalik

Patterns of Geologic Change

Linear- constant rate

Non-linear- inconsistent rate (*more common)

Non-repeating- doesn’t repeat

Repeating- repeats

• Periodic (rhythmic)- regularly

• Episodic- not regularly

Equilibrium

These changes compete & have a tendency toward this, but not often maintained long in a balanced state

Events

Subtle- gradual rise (uplift) & fall (subsidence) of earth’s surface (crust)/sea level

• Erosion

Dramatic- volcanoes erupting, tsunamis, earthquakes, floods, meteor impacts

• Global cooling & warming

Mass extinctions

Rapid extinction of a large number of diverse organisms around the world

• At least 60% of species present wiped out within 1 million years

• Caused by catastrophic events

• Rare events that open up possibilities for evolution (ex. Cretaceous period — Dinos eliminated, but give rise to mammals)

Background extinction

Lower average rate of extinction; certain populations reduced to zero bc of

• Normal environmental change

• Emerging disease

• Predation pressure

• Competition

1. Paleozoic, Ordovician

• Glacial & interglacial periods

• Rising/falling ocean levels

• Atmospheric changes

• CO2 stored

2. Paleozoic, Devonian

• Global cooling followed by warming

• Anoxic oceans

• Bolide meteor

3. Paleozoic/Mesozoic, Permian

• Extreme volcanic eruptions (Siberia)

• CO2 rise

• Global warming

• Anoxic oceans

• Bolide meteor

4. Mesozoic, Triassic

• Increased magma deposition in CAMP

• CO2 rise

• Global warming

• Calcification crisis in oceans

5. Mesozoic/Cenozoic, Cretaceous

Meteorite impact (Mexico):

• Iridium-rich layer deposited & Chicxulub crater aged at 65 mya

• Tsunamis, earthquakes, rapid global cooling

Most devastating mass extinction

End of Permian period

• More than 90% of all genera in late Permian oceans disappeared

• New populations of mollusks, new forms of coral, & other animals

Phanerozoic Eon

• Some fossils prior to Cambrian

• More “hard-bodied” organisms evolved & diversified in Cambrian/beyond

• Fossil Record more complete — Tax. & tissue bias, temporal

• 3 eras

Paleozoic era (“ancient life”)

541-252 mya

• Ends w/ obliteration of almost all multicellular organisms at end of Permian

Paleozoic life

Initial diversification of animals, land plants, & fungi

• Land animals appear 1st

• Primitive life

• Many invertebrates

• Earliest fish & amphibians

Paleozoic continental & climatic changes

• Supercontinent Gondwana & 8 other continents (S. hemisphere)

• Pangea forms

• Periods of warm climates, then glacial events

Paleozoic periods

1. Cambrian

2. Ordovician

3. Silurian

4. Devonian

5. Carboniferous

6. Permian

Mesozoic era (“middle-life”)

252-66 mya

• Begins w/ end of Permian extinction events

• Ends w/ extinction of dinosaurs b/t Cretaceous & Paleogene periods

Mesozoic life

• Dinosaurs

• Gymnosperms (conifers)

Mesozoic continental & climatic changes

• Pangea breakup

• Rising sea levels

• Arid climate = continental interior

• Humid climate = coastlines

• Mostly warm bc of high CO2 (GH effect)

• Minimal polar ice

Mesozoic periods

1. Triassic (mammals appear)

2. Jurassic

3. Cretaceous

Cenozoic era (“recent-life”)

66 mya - today

Cenozoic life

• Plants & animals look like those around today

• Mammals

• Angiosperms (flowering/fruting)

Cenozoic continental & climatic changes

• Continents in current positions

• Climate gradually cooled (glaciers in Antarctica)

• Grassland expansion

• Ice ages

Cenozoic periods (and epochs)

1. Paleogene (Paleo, Eo, & Oligocene)

2. Neogene (Mio, Pliocene)

3. Quaternary (Pleistocene)