Class 6A: Life in Space

Introduction to Astrobiology

Class 6: Life in Space

When Did Life Begin?

Early Origin of Life

• Fossil evidence indicates advanced lifeforms existed on Earth between 3.5 to 4.25 billion years ago.

• This timeframe corresponds to the near end of a period known as the heavy bombardment.

• Finding evidence from such an early time suggests life must have been widespread.

• We might expect that life on other worlds with conditions similar to early Earth would also rise rapidly.

• Implication: Life may be common throughout the Universe.

Where Did Life Begin?

Deep-Sea Vents

• Leading candidate for the origin of life is deep-sea vents.

• Deep-sea vents provide chemical energy that could fuel reactions necessary for life’s origin.

• Current extremophiles inhabit these environments, reinforcing their viability as cradles for early life.

How Did Life Begin?

A Theory for the Origin of Life

1. Organic Molecules on Early Earth

   • Organic molecules were abundant in certain environments on the early Earth.

2. Role of Clay Minerals

   • Clay minerals catalyzed the production of RNA and membranes that trapped RNA and other organic molecules, leading to the formation of pre-cells.

3. Pre-Cells as Factories

   • These pre-cells acted as microscopic factories where RNA evolved through molecular natural selection, with some becoming capable of self-replication.

4. RNA World Hypothesis

   • Both RNA and proteins evolved via molecular natural selection, eventually leading to true living cells capable of full self-replication.

5. Transition to DNA-based Life

   • Biological evolution within the RNA world ultimately led to the emergence of the first DNA molecules, which took over as the main hereditary molecule due to its advantages over RNA.

6. Uncertainty of Origin

   • There is uncertainty whether life actually originated this way, but the scenario seems plausible, and many experimental steps have been replicated in labs.

   • If an alternative scenario existed, it must have been equally feasible; otherwise, life would originate through the discussed method.

   • It is likely that life could arise in environments similar to early Earth.

Alternative Theory: Life Migrated to Earth

Panspermia Hypothesis

• Suggests that building blocks for life could form and remain stable in space environments (e.g., gas clouds, asteroids, and comets).

• Poses the question: Can life migrate from planet to planet?

Could Microbes Survive Transport to Earth?

Conditions for Survival

• For microbes to arrive intact on Earth, they must survive three critical phases:

  1. The impact that blasts them off their home world's surface.

  2. The time spent in space.

  3. The fiery entry into Earth's atmosphere.

The Space Environment

Key Characteristics

• Gravity:

  • Massive objects warp space-time and create acceleration towards their centers, often referred to as gravitational force.

  • Strength of gravity decreases with distance from the center of massive objects.

  • Objects 400 km above Earth's surface still experience gravity, although it is less intense.

Gravity Data Table

Weightlessness vs. Zero Gravity

• Weightlessness:

  • An object in free fall experiences the absence of weight.

  • An object will eventually strike whatever it is falling toward unless acted upon by another force (like a parachute) or is moving tangentially to the gravitational pull.

• Orbit:

  • An object with proper tangential velocity will fall towards Earth but continue moving sideways, resulting in an orbital path.

  • In orbit, objects are continuously in free fall towards Earth and experience weightlessness.

Temperature Variations in Space

• Temperature can vary greatly with altitude and time of day.

• In Low Earth Orbit (e.g., the ISS):

  • -150 °C in Earth's shadow.

  • 120 °C in direct sunlight.

• Surface of the Moon:

  • -173 °C at night.

  • 127 °C during the day.

Vacuum of Space

• Sea-level on Earth: particle density is about 10 trillion trillion molecules per cubic meter.

• In space, particle density drops to less than 10 atoms per cubic meter, resulting in effectively zero pressure.

Radiation Exposure In Space

• High-energy photons include ultraviolet, X-ray, gamma rays.

• Solar wind comprises a dilute plasma of high-energy electrons, protons, helium nuclei, and heavier ions.

• Galactic cosmic rays are high-energy protons and helium nuclei originating outside our solar system.

Orbital Debris

• Consists of micrometeoroids from comet and asteroid breakup and larger pieces of non-operational spacecraft and remnants from explosions in orbit.

Microbes in Space

Space Environment for Microbes

• The same key environmental factors affect microbes: gravity, temperature, vacuum, radiation, and orbital debris.

Radiation Exposure

• Radiation exposure can cause cell damage, mutation, or cell death with limits varying between species.

• Example: A three-year-long ISS experiment exposed certain radiation-resistant bacteria, having 10 redundant copies of DNA per cell, showcasing differences in survivability.

• Bacteria's outer layer died but protected the inner region during the exposure.

Microbial Survival and Transport

• Microbes could theoretically survive space but would likely not survive passing through a planet's atmosphere without additional protection.

Hitchin’ A Ride

• Meteorites can travel between worlds, with over 100 found to have originated from Mars.

• The likelihood of Earth, Venus, and Mars exchanging microorganisms via meteorite impacts is discussed.

Protection for Microbes

• Experiments show that embedding microbes within asteroid-like materials significantly increases their survival rates during transit through space.

Panspermia Probability

• The probability of a microbe surviving migration between planets depends on the journey's duration; some meteorites from Mars took millions of years to reach Earth, with varying survival rates from experiments.

Starmap Migration

• Migration across star systems is deemed unlikely due to a variety of factors, including prolonged exposure to harsh space conditions and low probabilities of encountering another planet.

Reasons to Consider Migration of Life

• Arguments suggest that the formation of life may be more complex than previously thought and that only a few worlds possess suitable conditions, thus the idea of Panspermia provides a broader context in astrobiology.

• Exploring other worlds, like Early Venus or Early Mars, raises questions about where life may have first emerged and indicates that Earth may not have been the first suitable location.

Effects of Space on Human Physiology

Space Motion Sickness

• Commonly referred to as space adaptation syndrome, results from conflicting signals sent to the brain from different sensory systems.

Redistribution of Bodily Fluids

• In microgravity, fluids distribute unevenly, causing symptoms such as headaches and congestion.

• The body can adapt by altering kidney functions and reducing blood volume.

Appearance Changes in Space

• Upon entering space, astronauts often experience "puffy face" and "chicken legs" due to fluid shifts.

Spinal Extension

• Lack of gravitational compression of spinal discs leads to temporary increases in height for astronauts in microgravity.

Muscular Atrophy

• Extended periods in microgravity result in muscle shrinkage, especially in postural muscles.

Bone Density Loss

• Continuous formation and resorption of bone are affected in microgravity, leading to reduced bone density over time.

Other Potential Health Issues

• Various health issues include altered perception of taste and smell, fatigue from radiation exposure, and the presence of kidney stones.

Summary of Findings on Space Environment

• Space presents harsh and potentially detrimentally environments for life forms as we know them, but ongoing research continues to identify possible mitigations and responses to these challenges.