Lecture 12- Geologic Time Scale Flashcards
what is the name for a calendar of events in Earths history
(a representation of time based on earths geologic record/rock layers
geologic time scale
- a tool breaking up/dividing history/time into usable, understandable segments/intervals
- divides up history of earth based on life-forms that existed during specific times
within geologic time scale, geologists divide history/time into ___ (4) + which is longest and shortest
in order from longest to shortest:
- eons
- eras
- periods
- epochs
segments are named and dated based on research carried out over more than a century
how do we know about lifeforms given that they go back billions of years
fossil
__ are essential to our understanding of geologic time scale
fossils
what is the remains or traces of an organism from passed preserved sediment or rock
a fossil
- geologically altered remains of a once-living organism and/or its behaviour
what is the study of fossils
- greek words
paleontology = ancient being study
from 3 greek words paleo, onto, and logo
- paleo = ancient
- onto = being
- logo = study
paleontology = scientist who studies fossils
what do fossils help determine
- age of rock relative to other rocks
- environnement in which rock formed
what is the history of earth as documented by fossils
fossil records
- different animal/plant/bacteria/fungi fossils
- in observing layers of rock, find that species appear, go extinct evolve and change environments
specific fossils are only found in ___
specific rock layers
- finding specific fossils in rock layers tells geologists how old rock is in relation to other in area
- finding specific fossils also enables geologist to match age of rock in one area to another area and even across continents if organism had large enough range
what is the use of fossils to help determine age of rocks
biostratigraphy
____ is destructive
fossilisation — process of becoming a fossil
T or F. most living things dont become fossils
True. remains are more often eaten/consumed or destroyed
- some parts of organism more likely to preserve than others
which parts of the organism are more likely to preserve and which are less + why
more likely:
- bones
- teeth
- shells
less likely:
- flesh
- organs
why: harder parts more resistant to destruction/decomposition over the years and less likely to be eaten
why are jellyfish rare in fossil records
they dont have any harder parts
what is the name for the fossils that depict organism behaviour + what behaviour does it depict
trace fossils
- footprints
- coprolites (fossilized dung)
- fossilized nests/burrows
to be considered a fossil, must have a ____ origin
biogenic
which means: made by/from living organisms
what is a word for made by/from living organisms
biogenic
why are oldest fossils difficult to confirm as biogenic
- no linger a trace of original biological material
- organisms may not resemble what we easily recognize
what is the oldest known fossil
- cyanobacteria (from rocks of western australia)
- dated 3.5 billion years ago
- note: oldest rocks only a little older (3.8 billion years)
- what we observe is stromatolites
what are stromatolites
- layered sedimentary formations created by photosynthetic (make their own food) microorganisms (organisms you can only see with a microscope) such as cyanobacteria
- layers of photosynthetic microorganisms (cyanobacteria) which formed layers and ultimately mounds over time
how tall are mounds
more than half a meter tall
living ____ still found today in marine environments
stromatolites mounds
any environment or situation where free oxygen (O2) is present
aerobic
___ organisms are organisms that require oxygen to survive
aerobic
any environment or situation/condition where “free oxygen” (O2) is absent
anaerobic
- may on train oxygen bound to other atoms such as nitrate (NO3-), nitrite (NO2-) or sulfite (SO32-) but cannot find free oxygen (O2)
anaerobic soil can be found where
- deep soils
- deep sea
- wetlands
- swamps
- bogs
a wetland/wet spongy ground that accumulates peat to deposit of dead plant animals, often mosses
bog
how many years can bog bodies be preserved for
thousands of years
what conditions helped the 2400 year old bog body found in a danish bog preserve
- lack of free oxygen
- lack of cold temperatures
- lack of acidic water
how do fossils form
- organism must die
- Predators/scavengers do not consume it or a least part
of it - Remains find themselves buried quickly, in soft sediments, to avoid being eaten, and rapid decay
- As layers of sediment/pile up on top of remains, rocks
form around the organism through lithification - Rocks forming around organism change shape and
composition of remains! - Empty spaces within body/organism can be filled with
sediment (eventually becoming rock) or can be filled with
minerals (deposited by groundwater) - Finally, rocks around fossil weathered/eroded away, allowing us to discover
these special and informative remains!
how long was organism be buried for fossil to form
thousands or millions of years
what is the ideal condition that organisms must be buried in to become fossils
- low free oxygen / anaerobic conditions
ex: - bogs
- wetlands
- swamps
- deep ocean
- deep lake
- under volcanic ash
what animal is fossilized in Redpath museum, McGill university
gorgosaurus
what sometimes happens during fossilization
organism itself completely dissolves leaving mold surrounded by rock
what are the two fossil types
**- mold fossils: **form when organism gradually dissolves away, leaving behind
impression of body, leaves, flowers, etc…
**- cast fossils: ** Same process (organism gradually dissolves away) but
impression/mold left behind filled with sediment that ultimately forms rock,
replacing original organism.
form when organism gradually dissolves away, leaving behind
impression of body, leaves, flowers, etc…
mold fossils
Same process (organism gradually dissolves away) but
impression/mold left behind filled with sediment that ultimately forms rock,
replacing original organism.
cast fossils
