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Activity 3.3

Get the Signature!

Focus Question: What is a biosignature?

A biosignature is a sign of present or past life.

•Fossils

•Tracks

•Burrows

•Chemicals

Focus Question 2: How does the study of biosignatures help scientists search for life on Mars?

By studying biosignatures here on earth, scientists

can train themselves to recognize the

signs of Martin life

Linda JahnkeMicrobiologist NASA Ames Research Center

Microbial Mats

• Layers of microorganisms

• Believed to be among the first forms of life

• May have been on Mars in the ancient lakes or oceans

Microbial Mats

Jahnke and fellow researchers:

• grow and analyze the living mats at Ames Research Center.

• develop methods to look for the chemical biosignatures of ancient microbial mats on Earth and Mars

Using Chemical Biosignatures of Microbial Mats

• show modern microbial mats are similar to those that existed billions of years ago on earth

• someday compare Earth’s microbial mats with mats from Mars

Chromatography* is used to determine the specific chemicals found in

microbial mats.

* A process in which a chemical mixture is passed through a material that separates it into is parts. This leaves a unique chemical signature

Activity 3.3 Get the Signature! Objectives

• Use chromatography to analyze biosignatures • Compare biosignatures from different life forms

• Draw conclusions about how biosignature scientists search for life on Mars

Teacher Preparation Chromatography Paper

• Tape each paper strip to the middle of a Popsicle stick

•With a pencil and ruler, draw a line across each paper 2 cm form the bottom

•Store in a zip-lock bag

Teacher PreparationPigment extraction

Carrots – Boil carrots for 25 minutes, crush them, add 5ml to a petri dish for each group

Spinach – Using a garlic press, crush fresh spinach. Put 5 ml of crushed spinach into a petri dish for each group

Chromatography PaperStudent Activity

• Dip a toothpick into the crushed spinach -paint a green line over the pencil line

•Allow the strip to dry - paint a second green line

• Repeat with cooked crushed carrot

Chromatography PaperStudent Activity

• Place strip into the cup –submerged in about 1 cm deep of isopropyl alcohol

• Wait 15 min, or until alcohol travels most of the way up strip

• Remove the paper strips and allow to dry

Chromatography PaperStudent Activity

• Observe bands of color

• Each band of color represents a different pigment that is present in the spinach or carrot

• These patterns the chromatograms - or chemical biosignatures

Observations/Conclusions

Families of pigments

•Carotenes

•Chlorophylls

•Xanthophylls

For Further Exploration

Calculate the retention factor (Rf) for each pigment –

Rf = Distance a component travels (Dx) Distance a solvent travels (Ds)

Thin Layer Chromatography (TLC)– greater speed, sensitivity and resolving power over paper.

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