6.2 - Biosignatures

Question 1

What is a biosignature?

Answer 1

A biosignature is defined as any characteristic element, molecule, substance, or feature that can be used as evidence of past or present life and is distinct from an abiogenesis process.

A biosignature is often called a biomaker.

Biosignatures are important for studying the history of life on earth and other planets.

Question 2

What are examples of lipid biosignatures?

Answer 2

Isoprenoids, hopanes, and sterols are all types of lipid biosignatures that can be used to identify the presence of past or present life on Earth and potentially on other planets.

Isoprenoids = Synthesis larger biomolecules

Hopanes= Used in cell membranes in bacteria

Sterols = They are involved in various cellular functions, including cell membrane stability, and are commonly used as biomarkers.

They are all molecular fossils

Overall, the identification of these and other lipid biosignatures can provide important clues about the composition and history of the environment in which they were produced, as well as the potential for life to exist or have existed in that environment.

Question 3

What is a biosignature assemblage?

Answer 3

A biosignature assemblage is a collection of different types of biomarkers that are indicative of past or present life in a particular environment. This can include various organic molecules, such as lipids, amino acids, and nucleic acids, as well as physical structures such as fossils or microbial mats.

The potential biosignature assemblage for a given environment will depend on a range of factors, including the type of organisms that inhabit that environment, the environmental conditions present, and the geological history of the area.

Identifying a biosignature assemblage can be a powerful tool for astrobiologists and geobiologists seeking to understand the potential for life to exist or have existed in a particular environment. However, it is important to note that not all biosignatures are definitive evidence of life, as some can be produced by abiotic processes as well. Therefore, identifying multiple independent biosignatures that support the presence of life is often necessary to increase confidence in the presence of extraterrestrial life.

Question 4

What components together create a biosignature assemblage that forms a comprehensive picture of a the biological and geological processes that occurred in a particular environment?

Answer 4

Isotopes: Isotopes are different forms of an element that have the same number of protons but a different number of neutrons. Stable isotopes, which do not decay over time, can be used to identify the source of various compounds in an environment, such as water or carbon dioxide. Isotopic ratios can also provide information about the metabolic processes of organisms, as some isotopes are preferentially taken up or excreted by living organisms.

Chemistry: Chemical analysis can provide information about the organic and inorganic compounds present in a particular environment. For example, the presence of certain minerals or chemical compounds can be indicative of biological activity, as some organisms can alter their environment through metabolic processes. Additionally, the ratio of different elements in an environment can provide clues about the history and evolution of that environment.

Minerals: Certain minerals can provide evidence of past biological activity. For example, the presence of certain carbonate minerals can indicate the activity of photosynthetic organisms, as they often consume carbon dioxide and produce calcium carbonate. Additionally, the presence of fossilized microorganisms in minerals such as chert can provide direct evidence of past life.

Organics: Organic molecules, such as lipids, amino acids, and nucleic acids, can be used to identify the presence of past or present life. Lipids and other biomolecules can be preserved in sedimentary rocks or other geological formations for millions of years, providing a record of the organisms that once lived in that environment. Additionally, the presence of certain organic molecules, such as methane or formaldehyde, can be indicative of biological activity.

Question 5

What is the problem with biosignatures?

Answer 5

They exist at different scales and so this requires different analytical techniques and instrumentation to find and measure them

Question 6

What are metabolic biosignatures?

Answer 6

Metabolic biosignatures refer to the unique metabolic profiles or patterns of molecules that are associated with specific biological processes or states.

Question 7

What do sulfur and sulphate reactions do?

Answer 7

SO4 —> H2S

Sulfur reduction and sulfate reduction can be considered as metabolic processes that can generate metabolic biosignatures.

• Sulfur reduction is the process by which elemental sulfur (S) is reduced to hydrogen sulfide (H2S) through various enzymatic reactions in microbes.
• Sulfate reduction, on the other hand, is the process by which sulfate (SO4) is reduced to sulfide (S2-) in microbes, also through various enzymatic reactions.

These biosignatures can be detected and quantified using various analytical methods. These biosignatures can be used to identify and monitor the activity of sulfur-reducing or sulfate-reducing microorganisms in various environments, such as soils, sediments, and water bodies.

Question 8

Methanogenesis as a metabolic biosignature

Answer 8

CO2 —> CH4

Methanogenesis can be considered as a metabolic biosignature because it is a distinctive metabolic process that generates unique metabolic products that can be detected and measured. Methanogenesis is the biological process by which microbes, such as methanogenic archaea, produce methane (CH4) from different substrates, such as carbon dioxide (CO2), acetate, or hydrogen (H2), through a series of enzymatic reactions.

(Methanogenesis can be detected and quantified through the production of methane.)

Question 9

Oxygenic photosynthesis (Fe, Mn, Mg) as a metabolic biosignature

Answer 9

CO2 —> O2

Oxygenic photosynthesis, specifically the production of oxygen (O2) and the use of Fe (iron), Mn (manganese), and Mg (magnesium) in the photosynthetic machinery, can be considered a metabolic biosignature. Oxygenic photosynthesis is the process by which plants, algae, and cyanobacteria use light energy to convert carbon dioxide (CO2) and water (H2O) into organic matter and O2 through a series of enzymatic reactions.

Question 10

What are organics?

Answer 10

Organic molecules have carbon and hydrogen as part of their structure.

Around 110 different organic compounds that have been detected in space.

Mostly comprised of CHNOPS elements

Example of organic molecules:
- Methane
- Ethane
- Propane

Question 11

Where are there organics in space?

Answer 11

Organic molecules have been detected in various environments in space, including in comets, asteroids, interstellar dust clouds, and planetary atmospheres and surfaces.

Overall, organic molecules are widespread in space and can provide insights into the formation and evolution of the solar system and the potential for life beyond Earth.

Question 12

Are there organic molecules on mars?

Answer 12

Organic molecules have been detected on Mars by various missions, including the Viking, Phoenix, and Curiosity rovers. The presence of organic molecules on Mars is significant because it suggests that Mars may have had the necessary ingredients for life at some point in its history, although the origin and nature of the organic molecules are still under investigation.

Question 13

How are there organics on mars?

Answer 13

• there are 100-300 tons of carbon delivered to the Martian surface per year, assuming a C content of 10%

Carbon, like other elements and molecules, can be transported to Mars through various processes, including meteorite impacts, volcanic activity, and interplanetary dust particles.

• Meteorite impacts are a common way that materials, including carbon, can be delivered to Mars. When a meteorite collides with Mars, it can create a shockwave that ejects material from the Martian surface into space. Some of this material can then travel through space and eventually reach Earth, where it can be studied to learn about the composition of Mars. Similarly, some material from Earth can also be ejected into space by meteorite impacts and travel to Mars.
• Interplanetary dust particles, which are small particles of rock and dust that are present throughout the solar system, can also transport carbon to Mars. These particles can be captured by Mars’s gravity and fall to the surface, where they can deposit carbon and other materials.

(- Carbon delivered by Interstellar dust particles (IDP’s) are dispersed globally)

Question 14

NASA Viking mission 1976

Answer 14

There were 2 orbiters and 2 landers

• It collected data for over 6 years
• It conducted experiments on the atmosphere and soil composition, meteorology and seismology

It’s main aim was to look for evidence of microbial life in the Martian soil and was first “Astrobiology” mission

Question 15

What did the Viking landers do?

Answer 15

They looked for microbial activity with 3 separate experiments. They conducted biology experiments based on what was known about microbial metabolism at the time.

• Used an arm to scoop up samples of surface soil for these experiments

Question 16

What were the 3 experiments conducted by the Viking landers?

Answer 16

1) Labelled release = It added nutrients to mars soil with radioactively labelled carbon to see if the carbon turned into CO2.

-If living organisms were present in the soil, they would consume the labeled nutrients and release radioactive carbon dioxide, which could be detected by instruments on the lander.

2) Gas exchange = It added nutrients to mars soil to see if gases such as methane or oxygen were released

• If living organisms were present in the soil, they would consume the nutrients and produce gases such as carbon dioxide, methane, and hydrogen.

3) Pyrolytic release = This experiment involved heating Martian soil samples to high temperatures in the presence of a gas that would react with any organic compounds present in the soil, releasing gases that could be detected by instruments on the lander.

• ## If organic compounds were present in the soil, they would be detected by this experiment.

Question 17

What was used to measure the organic compounds in the Martian soil?

Answer 17

GC-MS instrument was used by the viking landers to measure organic compounds in the Martian soil.

Gas chromatography, mass spectrometry - separated and detects chemical components

Question 18

What experiment was positive?

Answer 18

The labelled release experiment was positive

Question 19

What experiments were negative?

Answer 19

Gas exchange and Pyrolytic release

GC-MS was negative as well as no organics were found

Question 20

What were the conclusions made from the Viking lander mission?

Answer 20

Immediate conclusions:

• There was no life on mars
• Mars was a barren wasteland and not worth exploring so there was no exploration for over 20 years after.

There were some unexplained results:

• There should be organics even if they didnt produce life
• Why was the labelled release experiment positive?
  = had to wait until 2008, over 30 years after to find out the answer!

Question 21

What did NASA Phoenix Lander in 2008 do?

Answer 21

It used a robotic arm to dig p top soil and near-surface water ice for samples

• It discovered a salt called percolate (CIO4) in the Martian soil
• Perchoalte destroys organic compounds! Especially when heated up eg. Though the GC-MS analysis so is most likely why those experiments came back negative

Question 22

Why was the labelled release Viking experiment positive?

Answer 22

It was positive because the carbon-based nutrients added to the soil reacted with the percholate to produce CO2
= Percholate was found by the NASA Phoenix lander in 2008

Question 23

Why did our first attempt to find metabolic and organic biosignatures on mars fail?

Answer 23

1) We were looking for the wrong type of life (living, photosynthetic or heterotrophic soil microorganisms)

2) We didn’t know enough about the Martian geology and chemistry to design the right technology

Question 24

How has the Phoenix lander in 2008 been helpful for future Martian missions?

Answer 24

Percholate salts = found by the Phoenix lander

The way Martian soil was analysed for organic compounds was changed to stop them being destroyed by percholate salts.

Question 25

Chlorobenzene importance

Answer 25

Chlorobenzene is a volatile organic compound (VOC) that is commonly used as a solvent and chemical intermediate on Earth, but its detection on Mars would be significant because it is a complex organic molecule that could potentially indicate the presence of life or past life on the planet.

Question 26

What was the Cumberland sample?

Answer 26

The Cumberland sample was a drilled rock sample collected by NASA’s Curiosity rover on Mars in 2013 (from a crater).

The sample contained a variety of organic molecules, including chloromethane, a precursor to chlorobenzene, but no evidence of complex organic molecules or biological activity.

The discovery of organic molecules in the Martian soil and rocks, including the Cumberland sample, suggests that organic chemistry occurs on Mars and provides important clues about the planet’s history and potential habitability.

Question 27

Is there methane on mars?

Answer 27

Methane has been detected in situ on Mars by both ground-based telescopes and the Mars rover missions. Methane is a simple organic molecule that can be produced by both geological and biological processes, so its detection on Mars is of great interest to astrobiologists studying the potential for life on the planet.

Question 28

What was later discovered about methane on mars?

Answer 28

It was discovered after 5 years of measurements that methane is seasonal and localised (in 2018).

There are higher concentrations observed during the summer and lower concentrations of methane during the winter.

In addition, methane detections have been localized to specific regions of the Martian surface, such as the northern hemisphere and the Gale Crater, where the Curiosity rover detected a sudden spike in methane levels in 2013. The source of the localized methane emissions is still unknown, but possible explanations include geological activity, such as the release of methane from subsurface reservoirs or the interaction of water with rock, or biological activity, such as the activity of microbial life in the subsurface.

Question 29

Where does the methane on mars come from?

Answer 29

1) From the interaction between rocks in the subsurface and liquid water

2) From microbial life —> methanogens

3) From both

Question 30

How can methane come from the interaction between rocks in the subsurface and liquid water?

Answer 30

Methane is a light gas, and rises up to the shallow crust. Cold temperatures mean ancient methane can be stored as methane clathrate (trapped in water ice) deep in the Martian crust.

• still dont know if original source was biological or not though

Question 31

How can methane come from microbial life and methanogens?

Answer 31

Methane could be the metabolic bi-product of ancient or recently active methanogens

Such as primative microorganisms that get their energy from methanogenesis (this was an important metabolism in the archean on earth)

Question 32

Are there biosignatures on mars?

Answer 32

Observations can be explained by life but also by abiogenic processes so there are no biosignatures on mars (yet)

• there have been many scientific studies and investigations suggesting that the planet may have once been habitable and could potentially support microbial life.