The fossil record Flashcards
how old is earth
4.5 billion years old
what gives evidence of how old life is on earth
stromalities which are the first piece of evidence that life dates back to around 3.5 billion years ago
stromatolities
rock that is made by photosynthesising bacteria
what are the 8 steps of the geological timeline
- prokaryotes 2. photosynthesis 3. eukaryotes 4. multicellular organisms 5. cambrian explosion 6. land animals 7. mammals 8. flowering plants
extinction
the dying out of a species on a global or regional level
benefits of eextinctions
they opened up new niches that allowed for the rapid evolution of organisms to fill these niiches
benefits of ice ages
provide land bridges for travel (gene flow, migration, etc)
negatives of ice ages
conditions of rapid burial for fossilisation are less likely, cold and less food for organisms to survive
what causes extinction
human factors or natural catastrophies
two mass extinction periods
wiping out of dinosaurs in the cretaceous period (65myo) and extinction of giant mammals (10,000 years ago)
the fossil record
the information derived frommm fossils, is arranged in chronological order and helps us map the history of life on earth, placing species in appropriate geological tme franes
fossils
the preserved body, impressions or traces of a dead organism that provides evidence of life from the past
conditions of fossilisation
physical protection from scaverngers and decomposers, areas of rapid sediement accumulation, constant cool temps, low oxygen avliability and low light exposure
what is the first step of fossilisation
the remanants of an organism are rapidly covered by sediemnt (with little exposure to factors thst may increase the rate of decomposition)
second step of fossilisation
over time sediment layers build upon each other and compact until pressure cements them together to form sedimentary rock
third step of fossilisation
within this rock, the fossilised remains can takke many forms
5 steps in fossilisation of an animal
- animal dies 2. the body is covered by sediment, the soft tissues decompose and hard body structures becoome fossilised 3. sediment layers accumulate and the resultant pressure forms sedimentary rock 4. earths movement raises layers of the rocks to the surface 5. the rock erodes exposing the fossilised body structures
types of fossils
mineralised, mould, trace, index, transitional, cast
perminerlised fossils
fossil formed when mineral rich groundwater deposits minerals into organic material
how are mineralised fossils formed
part of the organism falls into the water, is rapidly covered by sediemnt, minerlas from surrounding rock.sediment leech into organism, organism breaks down and minerals replace it
mould fossils
when a living thing decomposes undersneath sediement, creating a cacity in the shape of the dead organism
cast fossils
a mould fossil is filled with sediment, the sedimentary rock with the mould erodes leaving a cast of the mould
what does the fossil record show (5)
life in the past was simple, many species that used to exist are eextinct, many extant species didn’t exist in the past, where species lived and when. transitional species between ancestral and modern species
index fossils
short-lived species whose fossils appear for a limited time in the fossil record, used to work out the relative ages of other fossils
requirements of index fossils
distinctive, abundant, distributed worldwide, easily recognisable and existed for a short perriod of time
transitional fossil
shows traits that are common to both its ancestral group and descendent group
primitive traits
a feature of a species that was possessed by an eariler ancestral species
derived traits
a feature unique to the descendent species and not found in the earlier ancestral species
why are transitional fossils rare
because evolution doesn’t occur at a steady pace (very fast then stops for a period or time - punctured equilibrium)
trace fossils
fossil or structure indicating the presence of an organism rather than organisms themselves (e.g footprints, burrws, dung)
what are the two ways fossils are dated
relative dating and absolute dating
relative dating
determins the relative age of a fossil by comparing its position to other fossils or rock in surrounding rock strata, based on the law of fossil succession
why can sedimentary rock be dated absolutely
as its made of sediments that have eroded from older sites
law of fossil succession
the principle that fossils of the same age will be in the same layer of sedimentary rock and fossils found in higher/lower sedimentary layers will be younger/older
what is the priunciple or correlation
uses index fossils to determine the relative age of rock strata
absolute dating
used to detrmine the absolute age of a fossil by measuring the realtive amounts of radioisotopes with known half lifes to their products
half-life
the time taken for the radioactivity of material taken in by a living organism to be reduced by half its initial value by a combination of biological elimination processes and radioactive decay
3 principles of absolute dating
- radioisotopes are unstable elements that will break down overtime into a more stable product 2. brekadown is mostly constant and can be modelled by calculatimg half-life 3. half-life describes the time taken for half the mass of a radioisotope to break down into its products
carbon dating
determining the ratio of carbon-14 to carbon 12 to determine the age of a fossil
how does carbon dating work
living organisms contain C14 naturally, afetr they die, the C14 within the organism is unstable and steadily breaks down into nitrogen 14, which is absorbed by the atomsphere
carbon 14 half-life
5730 years
for what fossils can caron dating be used
those that are younger than 50,000 years old
Potassium 40 - Argon 40 dating
measuring the ratio of Potassium 40 - Argon 40 in lava deposits can give the exact age of the lava and therefore the appox age of the sedimentary rock above and below the lava can be estimated
what are the negatives of Potassium 40 - Argon 40 dating
living things do not have potassium in them so Potassium 40 - Argon 40 dating can only be used to determine the realtive ages of fossils
benfits of Potassium 40 - Argon 40 dating
can be used to date fossils older than 50,000 years old becauyse of the long half-life
half life of potassium
1.3 billion years
dating period
the range of time since fossilisation in which a particular radioisotope series can be used, beyond this there is not enough raqdioisotope present to determine age
