Fossils, Relative Dating, & Geologic Time Scale

What kinds of questions can the fossil record help us to answer?

what the oceans looked like at different time periods, the evolution of whales, the types of organisms that existed in the past and how they moved, and how behaviors evolved. 

body fossil

body parts of an organism

trace fossil

a trace of the organisms existence in that area, such as footprints and nests. 

 Why are organisms that are buried rapidly more likely to fossilize than those that are buried slowly or not at all?

they are less likely to be destroyed.

Describe two ways an organism can become a fossil without being buried in sediment.

by getting trapped in a substance that protects it from destruction, like by being frozen or getting trapped in sap.

how does the benthic zone environment effect fossilization?

creates a lot of fossilization because it’s so close to land and the sediment from the land runs off and covers the dead organisms.

how do lake environments effect fossilization

creates fossilization because dead animals sink to the bottom and get covered with sediment.

how do rain forest environments effect fossilization

don’t create fossils easily because the rain causes decay and scavengers get to the dead organisms before sediment can.

Describe three factors that could prevent an organism from long ago from ever turning up in a fossil collection today.

 Not dying in the right place, not avoiding scavengers and decomposers, and having a soft body structure can prevent organisms from turning up in a fossil collection. 

How are geologic maps useful to paleontologists?

they show where certain types of rock are and some types of rock like sedimentary are more likely to have fossils in them than others.

BONUS: You have been hired by National Geographic Magazine to journey to Inner Mongolia in search of fossils. You have the good fortune to find a site filled with many fossilized leaves, teeth, bones, eggs and even footprints from a variety of creatures. Amidst this treasure trove of ancient life you find no trace of insects. Your research partner concludes that no insects lived here at that time. What other hypothesis might you suggest to your partner?

because insects are very unlikely to be preserved as fossils but have such a large population, there probably were insects living in that area, they just didn’t fossilize.  

fossilization process

dead plant/animal is buried by sediment that then turns into rock

molds

if a fossil dissolves out of rock a hollow depression is created

casts

materials can seep into a mold and form a copy

carbonaceus film

thin carbon film resomboling s sihouette, high temps and pressure alters chemical makeup of organism

4 charecteristics of index fossils

easily recognizable, abundant, widespread in occurance, only existed within short time period

index fossil examples

trilobite, echinoid, coral, graptolite, brachiopods

relative dating

process of placing events in the sequence which they occured

superposition

order of oldest to youngest in an undisturbed sequence

cross cutting relationships

intrusion is always younger than rock it intrudes

unconformities

represents where rock layers are missing in seuquence, can be caused by erosion

Angular unconformity

• Happens when younger, flat strata are deposited on top of older strata

• How? Original strata get tilted and over time the surface is worn down

angular conformity image

fault rules

A fault is always younger than the rock it cuts through. To deter- mine the relative age of a fault, geologists find the relative age of the youngest layer cut by the fault.

rock layer sequence of events

Sedimentary layers were first, then the folding occured, because the igneous intrusion did not fold with the sedimentary layers, then the fault comes, becuase the igneous intrusion and layers were all shifted up.

uniformitarianism

theory that changes in the Earth’s crust over time have resulted gradually from continuous and uniform actions.

normal fault

hanging wall moves down (sit on)

reverse fault

hanging wall moves up (hang on)

strike slip fault

no verticle displacement

when was the majority of earths history?

4 bil years in the precambrian era

why is the precambrian era rock record hard to interpret?

old, bent, lacks fossils

shields

a large area of exposed Precambrian-age crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas.

precambrian life forms

oldest life forms, resemble today’s bacteria made up most fossils

what was the paleozoic era the age of?

invertabreas

cambrian explosion

rapid increase in life forms

cambrian period known for…

triolites and brachiopods (index fossils), 1st vertabreas, all life existed in ocean

ordovician period

graptolites (index fossil), relatives of squids, snails, sea stars, clams, corals

silurian period

1st land animals (relatives of spiders, scorpians, millipedes), 1st land plants (club mosses)

denovian period

“age of the fishes”, 1st forests

carbiniferous period

1st reptiles, insects increased, coal deposits

permian period

mass extinction (marine invertabre and plants), marine cephalopods and reptiles survive

mesozoic era

“age of reptiles”, known for mild climate, dinosaurs

triassic period

1st dinosaurs (small, moved quickly), ammonites (index fossil), pangea, ferns numerous

jurrasic period

numerous bigger dinosaurs, 1st insects that change form (metamorphisis), 1st true mammals and birds

cretaceous period

largest dinosaurs, flowering plants and decdius tress, mass extinction from asteroid

cenozoic era

age of the mammals, more known about this period than any othe

paleogene period

major mountain ranges formed, went from warm to cool climate, 1st meat eating mammals

neogene period

1st grasses, birds evolved, scorpions, bees, and beetles thrived, modern forms of elephants, horses, camels

quaternary period

2 mya to present, humans appear, forming and thawing cycles of glacial ice, mammals competing w/ humans went extinct