Biosignatures — MCQs - MCQs Answers

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1. What are biosignatures?
(A) Geological formations caused by erosion
(B) Chemical, physical, or biological indicators of life
(C) Artificial satellites orbiting a planet
(D) Evidence of volcanic activity

2. Which gas is a strong biosignature when found with methane?
(A) Oxygen (O₂)
(B) Nitrogen (N₂)
(C) Carbon monoxide (CO)
(D) Argon (Ar)

3. The presence of both oxygen and methane in a planet’s atmosphere suggests:
(A) Stable weather cycles
(B) Possible biological processes
(C) Absence of water
(D) Volcanic eruptions

4. Which mineral structure is a classic biosignature on Earth?
(A) Stromatolites
(B) Quartz crystals
(C) Basalt columns
(D) Feldspar deposits

5. What is the “red edge” in biosignature studies?
(A) Reflectance pattern caused by vegetation
(B) Edge of a planetary orbit
(C) Infrared absorption of CO₂
(D) Boundary of habitable zone

6. Which molecule is considered a molecular biosignature?
(A) Chlorophyll
(B) Helium
(C) Silicon
(D) Argon

7. Which biosignature can be confused by abiotic processes?
(A) Ozone (O₃)
(B) Oxygen (O₂)
(C) Methane (CH₄)
(D) All of the above

8. What is a “false positive” biosignature?
(A) A detection that proves intelligent life
(B) A non-biological process mimicking life signals
(C) A failed telescope observation
(D) A meteor impact signal

9. Microfossils found in ancient rocks are:
(A) Morphological biosignatures
(B) Molecular biosignatures
(C) Atmospheric biosignatures
(D) False biosignatures

10. Which gas layer on Earth protects biological life and acts as a biosignature?
(A) Nitrogen (N₂)
(B) Ozone (O₃)
(C) Carbon dioxide (CO₂)
(D) Hydrogen (H₂)

11. Which rover detected organic molecules on Mars?
(A) Opportunity
(B) Curiosity
(C) Spirit
(D) Perseverance

12. Why is water considered an important indirect biosignature?
(A) It forms only on gas giants
(B) It is essential for biochemical reactions
(C) It blocks UV radiation
(D) It produces methane naturally

13. Which combination of gases indicates strong potential for life?
(A) O₂ and CH₄
(B) CO₂ and N₂
(C) H₂ and He
(D) Ar and Ne

14. Which telescope is designed to search for atmospheric biosignatures?
(A) Kepler
(B) Hubble
(C) James Webb Space Telescope (JWST)
(D) Chandra

15. Why is oxygen alone not a definitive biosignature?
(A) It is unstable in atmospheres
(B) It can be created abiotically from water photolysis
(C) It always escapes into space
(D) It requires carbon dioxide to exist

16. Stromatolites provide evidence of:
(A) Ancient microbial life
(B) Volcanic eruptions
(C) Abiotic methane
(D) Acidic oceans

17. Which of these is a surface biosignature?
(A) Polar ice caps
(B) Vegetation reflectance patterns
(C) Ocean tides
(D) Crater impacts

18. Methanogens produce which gas as a biosignature?
(A) Oxygen
(B) Nitrogen
(C) Methane
(D) Argon

19. Which atmospheric gas is most stable without life processes?
(A) Oxygen
(B) Nitrogen
(C) Methane
(D) Ozone

20. Why are biosignatures important in astrobiology?
(A) They identify gravity of planets
(B) They measure star brightness
(C) They indicate potential for life
(D) They track comets

21. Which biosignature can indicate photosynthetic organisms?
(A) Red edge reflectance
(B) Infrared radiation
(C) Nitrogen isotopes
(D) High carbon monoxide levels

22. Lipid molecules preserved in rocks are examples of:
(A) Molecular biosignatures
(B) Atmospheric biosignatures
(C) Morphological biosignatures
(D) False positives

23. Which type of biosignature is most likely preserved in ancient rocks?
(A) Morphological
(B) Atmospheric
(C) Surface
(D) False positive

24. Which gas is often linked to volcanic activity, not life?
(A) Carbon dioxide
(B) Oxygen
(C) Methane
(D) Ozone

25. Why is methane a potential biosignature?
(A) It only forms through volcanoes
(B) It is unstable and needs replenishment, often biological
(C) It always coexists with nitrogen
(D) It blocks UV radiation

26. Which exoplanet detection method helps identify atmospheric biosignatures?
(A) Radial velocity
(B) Transit spectroscopy
(C) Direct imaging
(D) Microlensing

27. Which chemical is a possible false negative biosignature?
(A) Oxygen
(B) Carbon monoxide
(C) Nitrogen
(D) Methane

28. Why is nitrogen not a strong biosignature?
(A) It is too reactive
(B) It is geologically abundant and stable without life
(C) It always combines with methane
(D) It is only found on Earth

29. What is the study of biosignatures on exoplanets called?
(A) Planetology
(B) Astrobiology
(C) Cosmology
(D) Meteorology

30. Which spectral feature indicates chlorophyll presence?
(A) Blue absorption edge
(B) Red edge reflectance
(C) Infrared emission line
(D) Ultraviolet peak

31. Which biosignature would suggest oceanic phytoplankton?
(A) Oxygen buildup
(B) Methane absorption
(C) Nitrogen depletion
(D) Ozone loss

32. Why is ozone considered a biosignature?
(A) It can only form from volcanoes
(B) It results from oxygen produced by life
(C) It blocks water formation
(D) It is the heaviest gas

33. Which biosignature could be confused with abiotic methane from hydrothermal vents?
(A) Ozone
(B) Methane
(C) Oxygen
(D) Carbon dioxide

34. Isotopic ratios of carbon (¹²C vs ¹³C) can be biosignatures because:
(A) Life prefers lighter isotopes
(B) Life avoids heavy isotopes
(C) Rocks store only ¹³C
(D) Oxygen blocks isotope changes

35. What is a morphological biosignature example?
(A) Microfossils
(B) Methane in the air
(C) Chlorophyll absorption
(D) Vegetation reflectance

36. Which atmospheric gas is unstable without biological input?
(A) Methane
(B) Oxygen
(C) Both A and B
(D) Nitrogen

37. Pigments such as carotenoids are:
(A) Mineral biosignatures
(B) Molecular biosignatures
(C) Morphological biosignatures
(D) Geological false positives

38. Which biosignature is linked to cyanobacteria activity?
(A) Stromatolites
(B) Methane plumes
(C) Ozone depletion
(D) Acidic lakes

39. Which biosignature would JWST most likely detect in exoplanet atmospheres?
(A) Ozone and methane
(B) Heavy metals
(C) Helium clouds
(D) Hydrogen-only layers

40. Which biosignature indicates photosynthetic oxygenic life?
(A) O₂
(B) CH₄
(C) CO₂
(D) N₂

41. Which biosignature is considered the most reliable for complex ecosystems?
(A) Methane
(B) Oxygen and methane together
(C) Nitrogen
(D) Sulfur dioxide

42. Which mineral biosignature forms from microbial sulfur metabolism?
(A) Gypsum deposits
(B) Pyrite structures
(C) Stromatolites
(D) Feldspar crystals

43. A sudden rise in oxygen in Earth’s history is known as:
(A) The Great Oxidation Event
(B) Carbon Crisis
(C) Nitrogen Burst
(D) Methane Era

44. Which biosignature would suggest recent biological activity?
(A) Methane plumes
(B) Fossilized stromatolites
(C) Ancient isotopes
(D) Water ice

45. Which biosignature is most relevant for detecting surface vegetation?
(A) Red edge reflectance
(B) Infrared emission lines
(C) Methane absorption
(D) Nitrogen depletion

46. Which biosignature is evidence of metabolic waste gases?
(A) Methane and oxygen
(B) Nitrogen only
(C) Helium isotopes
(D) Hydrogen loss

47. Why are isotopic biosignatures useful?
(A) They remain preserved for billions of years
(B) They require sunlight
(C) They vanish quickly
(D) They occur only on Mars

48. Which biosignature could appear as surface discoloration on a planet?
(A) Microbial mats
(B) Nitrogen gas
(C) Ozone
(D) Helium

49. Which biosignature is most likely to indicate anaerobic life?
(A) Methane
(B) Oxygen
(C) Ozone
(D) CO₂

50. Why are biosignatures central to exoplanet studies?
(A) They measure planetary mass
(B) They provide evidence of potential life
(C) They confirm star types
(D) They detect asteroid belts

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