Bug Fossilization - a geologists perspective

Tomas Hode

Portland State University

Proving that it was alive..

What to look for when it comes to fossil viruses?

(Analysis – what to analyze, and how?)

Outline

Ok – I see a lot of things in my rocks.

Round things, elongated things, rod-shaped things, carbonaceous things, isotopically depleted things, etc., so what is required to convince me that it was alive?

Stuff in rocks

Just to go through the standard things:

Context (my problem, not your problem)- Compatible with life?

Exclusivity - Morphology (possibly)- Chemistry (yes)- Isotopes (?)- Element ratios (?)

What could convince me that it was alive?

1. Fossilization can preserve morphology, but if non-specific it is of little help.

2. Organic molecules lose functional groups – lipid backbones preserved if we are lucky. Isotopes not really a help unless extreme fractionation or certain context.

3. Discrepancy between recently fossilized material and ancient rocks…

We have some problems here…

Example of difficulties

30 μm

Round graphitic features

ErYAG ablation of dental tissue

(Bonus image)

Instant fossilization can give nice preservation, but with time this is changed – cell preservation highly unusual in very ancient rocks.

Modern vs. Ancient preservation

Ok, we have a problem here – the mechanisms of preservation gives you only rudimentary information in the rock record.

Preserved morphology is of no help when it comes to viruses unless it can be correlated with e.g. chemistry.

What about viruses in the fossil record?

Exclusivity:

- Morphology (small round things..)

- Chemistry (virus specific lipids?)

- Isotopes (?)

- Element ratios (?)

What could convince me that it was a virus?

Context:

What about fossil viruses inside fossil microbes?

What could convince me that it was alive?

Remember – these are the only thing we can analyze:

- Morphology

- Elements

- Chemistry

- Isotopes

Methods/Analysis

Sputtering/etching/tomography

ToF-SIMS mapping of lipids

NMP RBS for C isotopes (D/H ratio?)

What could element ratios tell us?

Methods/Analysis

Ideal case:

Spatial correlation between viro-lipids (at high lateral resolution) and morphological features preserved inside a fossilized microorganism.

Thoughts/conclusion