Evidence of Evolution

What are phylogenetic trees

Visual representation of relatedness of species and where common ancestors are shown

What conditions help preserve DNA and how they do so

• Extreme cold- dramatically slows down chemical breakdown of nucleic acid

• Temperature stability- prevents physical cracking and weathering of bone matric that exposes DNA to decay

• Dryness- reduces hydrolysis, which breaks bond in DNA backbone

Why id DNA rare to find in fossils older than 400,000 years old

Due to DNA being chemically fragile, when organism dies, enzymes water and micro-organisms start breaking chemical bonds holding DNA strand

How do Scientists compare ancient DNA and protein sequences

Align matching molecular letters/ amino acids to count differences and build evolutionary family trees

How does comparing DNA and protein sequences work

• Sequence alignment: line up DNA nucleotides or protein amino acids side by side to find corresponding positions

• Counting mutations: researches count mis-matches, each change representing a mutation

• Turn matches into % score: higher similarity means more recent common ancestor

• Phylogenetic trees: information is used to make phylogenetic trees which shows relatedness

What is a molecular clocks

a technique that uses mutation rates of biomolecules like DNA, RNA, proteins and mtDNA to estimate when 2 or more species diverged from one common ancestor

What does molecular clocks measure

measures number of accumulated mutations in DNA or protein sequence between species

Why is mtDNA preferred in use of molecular clocks

mtDNA acts as a highspeed molecular clock as it has a higher rate of neutral mutations than nuclear DNA mutation are random due to no recombination

What is a fossil

preserved trace left by previously living organism

why is rapid burial important for fossilisation

cuts off oxygen, blocks scavengers and decreases conditions of decay, preserving organism long enough to become a fossil

What material is best for preserving fossils

• sedimentary rock

• Ice

• Tar pits

• Amber

what location is best for preserving fossils

• deep lake beds

• oceanic floors

• quiet river flood plains

what processes prevent fossilisation

• biological decay by bacteria and fungi breakding down tissue

• oxygen exposure

• erosion, preventing fossilisation as formations needs stable sedimentary rock

• scavengers consume organism before it can fossilise

what is dating

determining age of material

what are the 4 conditions required to form fossils

• quick burial of material

• presence of hard body parts

• absence of decaying organims

• long period of stability ( left alone)

Why are there gaps in fossil record

• most dead organism quickly decompose or are eaten and cant fossilise

• fossilisation is a chance occurrence

• only a small proportion of fossils that exist have actually been discovered causing gaps

why are fossils of early human ancestors rare

• rare due to early human groups living in small numbers in areas where fossils were hard to form

• early humans didnt practice intentional burial until later mking erosion and decomposition easier

What is stratigraphy

study of layers or strata using principle of superposition which assumes that in sedimentary rocks, layers on top will be younger than layers at bottom

what is Relative dating

determines relative order of soil/rock layers, establishing sequence of order vs younger

What is absolute dating

determines actual age of fossil, using radioactive isotopes and their decay

what is the difference between absolute dating and relative

absolute dating gives numerical age whereas relative gives relationship between fossils

• both however used together create more accurate fossil record

what processes destory existing fossils

• erosion: wears down and ripes away exposed fossils at surface

• acidic groundwater: dissolves mineralised bones and shell structure underground

• metamorphism: extreme tectonic heat and earth pressure melts, crush and warp surrounding rock and fossils inside it

what enviornmental conditions are best for fossil formation

• soil should be alkaline as minerals in bones are not dissolved

• low oxygen to no oxygen as it slows decay as bacteria and fungi that cause decay cant survive

why is wet acidic soil bad for fossilisation

wet acidic soils dissolves minerals in bones, preventing fossilisation

what is potassium argon dating

absolute dating method based on decay of radioactive potassium to form argon

what age fossils can potassium argon dating do and why

• can only date rocks older than 100,000 to 200,000 years old

• why→ potassium 40 has a half life of 1.3 billion years allowing older sample to be dated

explain how potassium argon dating works ( idea behind it)

• potassium 40 is a radioactive isotope that decays into argon 40

• decay is extremely slow, but constant

• as rock ages, proportion of potassium 40 decreases while argon 40 increases

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why is argon a good detection tool

argon is a noble gas and is not commonly incorporated into rocks except when produced through radioactive decay

how is age of fossil determined using potassium argon dating

some suitable rock of the same age as fossil must be available and age of fossil is determined by inferring from age of rock

what rock type is suitable for potassium argon dating

igneous and metamorphic rocks

why is potassium argon dating useful

it can date fossils older than 1 million years due to large half life of potassium

what is carbon dating

method based on decay of radioactive isotope carbon 14 into nitrogen 14

what are the limitations of carbon dating

• material being dated must contain organic compounds ( once living)

• can only date reliably material up to 60,000 years due to half life of C-14 being 5730

• amount of C-14 in atmosphere varies meaning carbon dating results needs to be taken with caution

what absolute dating method can be used for volcanic rock fossils

• potassium argon dating

• Argon-argon dating

3 strengths of absolute dating

• gives an actual numerical age

• provides more precise age

• useful for dating very old material

limitations of absolute dating

• not all fossils can be directly dated

• can be affected by contamination, which can make calculated age inaccurate

• can be expensive and time consuming

strengths for relative dating

• determines whether a fossil is older or younger than another fossil

• can be used when absolute dating isn’t possible

• useful in establishing sequence of events

limitations of relative dating

• does not provide exact age

• original order of rock layers can be disturbed by geological processes

• only provides age comparision

what technique do scientists use to extract and analyse ancient DNA from fossils

• paleogenomics techniques

• use PCR to amplify DNA when needed

• bioinformatics to analyse DNA

what challenges do scientists face with extracting ancient DNA from fossils

• Very small quantities of DNA are usually present.

• DNA can be damaged or degraded over time.

• DNA can be contaminated by microorganisms or modern human DNA.