Advanced evidence type 2 - diatoms Flashcards
What is a diatom?
A type of phytoplankton, which is a eukaryotic algae
- cell wall is made of silica
- primarily exist in water and are also found around bodies of water.
-They make a significant proportion of the earth’s biomass and are nearly half the organic material found in the ocean
-Significantly contribute to sequestering carbon and producing oxygen
why are diatoms good for the planet?
Fix 120 Gigatonnes of CO2 every year through photosynthesis
produce 20-50% of the oxygen on the planet every year
vital for the long term sequestering of carbon dioxide for a long period of time
How can diatoms serve as form of forensic trace evidence?
they are a diverse group of species with small size range (2 to 5 micrometers) which makes their entry inside the body organs feasible
they have a hard silica wall which is resistant to the chemical changes - helps in maintaining the intact structure of diatoms from body or clothes
organs get blended with putrified bodies and only bones left but diatoms can still be recovered even when little other evidence is available
their growth corresponds to certain specific parameters of the environment - analysis therefore allows the cause and site of death to be concluded
wide range of study has been done on the taxonomy of diatoms due to which species are easy to identify and trace
What factors affects the transfer and persistence of diatoms?
The highest transfer to open weave and medium rough textured materials.
seasonal variation
morphology of the diatom
What was the Stenger’s pond attack in 1991?
two young boys fishing on a pond were beaten and drowned into a pond by a group of teenagers
no evidence such as fingerprints could link the suspects to the crime scene except mud on trainers
diatoms extracted from mud on the trainers, victims and a reference sample of mud at the pond were compared
these samples had shared 25 species of diatoms in common
the population ratio was also compared which matched between all samples increasing discrimination certainty.
The teenagers were convicted in 1992.
What are the caveats of diatoms?
chances of cross contamination and secondary transfer
learning systems are still emerging in order to speed up identification workflows and enable the usage of diatoms as trace evidence
this requires complex reference libraries which can be tedious
What is foraminifera?
single celled organisms, the majority live on the sea floor and have an external hard shell
There is limited usage of these as trace evidence however, it was shown in the case of Aldo Moro (1978) who was kidnapped and murdered.
What are phytoloiths?
Plant microfossils made of silica
can be used for tracing plant-human interactions
