lecture 6 Flashcards
How do we know about these life-forms given that they can go back
billions of years?
FOSSILS
What are fossils?
➢ remains (e.g., shells, skeletons) or traces (e.g., worm burrows,
footprints) of an organism from past preserved in sediment or rock
➢ geologically altered remains of a once-living organism and/or its
behaviour
What is palaeontology?
➢ study of FOSSILS
➢ from 3 Greek words, PALEO, ONTO and LOGY!
➢ PALEO = ancient, ONTO = being, LOGY = study.
➢ PALEONTOLOGY = ancient being study!
➢ PALEONTOLOGY = scientist who studies fossils.
With help of fossils what can geologists determine?
➢ age of a rock relative to other rocks
➢ environment in which rock formed
What is a fossil record?
➢ history of Earth as documented by FOSSILS.
➢ different periods of GEOLOGIC TIME /different layers of rock
have different animal/plant/bacteria/fungi FOSSILS
➢ in observing layers of rock, find that species appear, go
extinct (i.e., disappear) evolve and change environments
Given that specific FOSSILS only found in SPECIFIC ROCK
LAYERS
➢ finding specific FOSSILS in rock layer tells geologists how old
rock is in relation to other rocks in area
➢ finding specific FOSSILS also enables geologists to match
age of rock in one area to another area and even across
continents if organism had large enough range
What is biostratigraphy?
use of FOSSILS to (help) determine age of
rocks
What is fossilisation?
FOSSILISATION (i.e., process of becoming a FOSSIL) is
“destructive”
Do most living things become fossils? And why?
While all living things (e.g., plant, animal, bacteria, fungus) can
become a FOSSIL, most do not!
Remains are more often eaten/consumed or destroyed.
Some parts of organisms (e.g., bones, teeth, shells) more likely
preserved than others (e.g., flesh, organs).
Why?
These harder parts more resistant to destruction/decomposition
over the years and less likely to be eaten
What is trace fossils?
FOSSILS depicting organism behavior
including:
➢ footprints,
➢ coprolites (fossilized dung),
➢ fossilized nests/burrows.
Can any rock be considered fossil?
To be considered a FOSSIL, must have a BIOGENIC origin.
BIOGENIC = made by/from living organisms.
Often, oldest FOSSILS difficult to confirm as BIOGENIC since:
➢ no longer a trace of original biological material
➢ organisms may not resemble what we can easily recognize.
What is the oldest known fossils?
➢ CYANOBACTERIA from rocks of Western Australia
➢ dated to 3.5 billion years ago
➢ NOTE: oldest rocks only a little older (3.8 billion years old)
➢ 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 (e.g.,
CYANOBACTERIA) which formed layers and ultimately
MOUNDS over time
What is aerobic and anaerobic?
AEROBIC:
➢ any environment or situation/condition where free
oxygen (O2) is present
➢ AEROBIC organisms are organisms that require
oxygen to survive.
ANAEROBIC:
➢ any environment or situation/condition where “free
oxygen” (O2) absent.
➢ NOTE: may contain oxygen bound to other atoms
such as in nitrate (NO3
-), nitrite (NO2
-) or sulfite
(SO3
2-) but cannot find free oxygen (O2).
Examples of anaerobic soils.
Such conditions found in deep soils, deep sea but
closer to home, ANAEROBIC soils can also be
found in wetlands, swamps, bogs, etc…
What is a bog?
BOG: a wetland/wet spongy ground that accumulates
PEAT due to deposit of dead plant materials, often mosses.
How do fossils form?
Firstly, organism must die (Nobel Prize statement)!
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
Ideally remains buried in low free oxygen or ANAEROBIC conditions (e.g., bogs, wetlands, swamps, deep ocean, deep lake, under volcanic ash).
Must be buried for thousands or millions of years.
As layers of sediment/pile up on top of remains, rocks form around the organism through LITHIFICATION
(COMPACTION and CEMENTATION).
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).
Name the two types of fossils that can be formed?
MOLD FOSSIL: form when organism gradually dissolves away, leaving behind
impression of body, leaves, flowers, etc…
CAST FOSSIL: Same process (organism gradually dissolves away) but
impression/MOLD left behind filled with sediment that ultimately forms rock,
replacing original organism
