EVS Chap 2 Habitability

Chemosynthesis

process by which certain microorganisms produce energy from chemical reactions by oxidizing reduced inorganic compounds

*NO SUNLIGHT

• 4.4Ga first life forms around hydrothermal vents at bottom ocean used reduced volcanic compounds for chemosynthesis

Photosynthesis

process that allows organisms to generate organic matter (glucose and O2) using light energy, water, and carbon dioxide.

• greatly increased amount O2 in oceans, and depletion of CO2 and iron

Cyanobacteria

A type of bacteria that converts sunlight to energy producing oxygen (photosynthesis)

Banded Iron Formations (BIFs)

Geological formations characterized by alternating layers of silica (chert) and iron minerals like hematite (Fe₂O₃) and magnetite (Fe₃O₄)

*O₂ accumulation led to this (released O₂ oxidized reduced iron (Fe²⁺) to oxidized iron (Fe³⁺))

Great Oxygenation Event (GOE)

A major event that occurred approximately 2.4 to 2 billion years ago, marking the accumulation of oxygen in the atmosphere.

• anaerobic organisms had to adapt to aerobic conditions

• see expansion and diversification of life from simple prokaryote bacteria to more complex life with membrane and nucleus

what has accumulation of O2 in atmosphere allowed?

• Oxygenation of the oceans, leading to significant chemical changes

• Oxic respiration enabled the evolution of more complex organisms by providing more energy

• Formation of the ozone layer (O₃), which protects life from harmful UV radiation and allowed terrestrial life to diversify

• Oxidation of methane, a greenhouse gas, contributed to reducing the greenhouse effect and lowering Earth's temperature

Neoproterozoic

1-500 Ga earth went through period of intense climate upheavals marked by episodes of “Snowball Earth”

Snowball Earth - how did it promote development of more complex organisms?

Periods in the Earth's history when the planet was believed to be almost entirely covered in ice *liquid water still present around equator

• this accelerated erosion via glaciers → releasing nutrients (ex. phosphorus) → cyanobacteria blooms → O2 increase (and decrease CO2) → development of complex organisms

Phanerozoic Era

golden age for terrestrial habitability

brought favourable and stable conditions for biodiversity, protective atmosphere, balanced biogeochemical cycles

Earths Radiative budget

inventory of energy received and lost by earths climate system, soil-atmosphere-oceans

faint young Sun paradox

4.5 Ga when Earth formed Sun was 30% dimmer than today (yet still had liquid water and relatively warm climate)

Sun gradually increased in brightness causing Earth to receive more solar radiation thus impacting evolution of climate

solar radiation

all electromagnetic waves (UV, visible, Infrared) emitted by Sun, majority made up of visible light

how much energy is received from sun

342 W m^-2

how much energy is reflected

107 W m^-2

(77 by atmosphere and 30 earth surface)

How much energy is absorbed

235 W m^-2 (67 absorbed by atmosphere by air molecules and clouds, 168 absorbed by earths surface)

what accounts for earths average temperature of 15 degrees C? It should be much lower at -18

Greenhouse effect - GHGs absorb and emit infrared rays, trapping energy (heat) within the atmosphere

primary greenhouse gases (GHGs)

water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrogen oxide (N2O)

how does the GHG effect work?

Sun sends energy (visible light) → absorbed by earths surface and heats up → earth emits energy (infrared radiation) but not all heat escapes → GHGs act as sleeping bag keeping heat inside → trapped heat is sent back down to Earth warming the planet

Dynamic equilibrium the total energy Earth receives from the Sun is equal to the energy it emits (390 W/m²) → Contributes to stable and habitable climate

carbon cycle

moves carbon (C) between the atmosphere, oceans, land, and living organism, thus controlling the amount of carbon dioxide (CO₂) in the atmosphere

contributes to stable and habitable climate

carbon cycle early earth

most of C in atmosphere came from volcanos. plate tectonics promote outgassing of CO₂ from volcanos.

silicate weathering feedback loop

how earths climate is stabilized:

temp warm: chemical weathering of rocks accelerates calcium delivery to oceans. Calcium combines with CO2 to form rock (calcium carbonate) trapping CO2 in carbonates → less greenhouse effect → colder planet

temp cool: weathering of rocks slows because less rain and colder, allowing more volcanic CO2 to build up in atmosphere → increasing greenhouse effect → warmer planet

feedback loop of carbon sequestration in plants and organic matter

increase in plants → increase capture CO2 → stored in organic matter → cooling climate → plant growth becomes limited → reduces carbon sequestration in organic matter → promotes warming

milankovitch cycles

cyclical variations in earths orbit and orientation, influencing amount and distribution of solar energy → key role in climate

Eccentricity

100,000 year cycle

• Earth’s orbit changes shape between more circular and more elliptical.

• This affects the distance between Earth and the Sun, changing season intensity.

• More elliptical orbit = greater difference in solar radiation between seasons.

Obliquity

41,000 year cycle

• The Earth’s axis tilt varies between 22.1° and 24.5°.

• More tilt = stronger seasonal contrasts (hotter summers, colder winters).

• This affects polar caps (ice formation and melting).

Precession

Precession

• Earth’s axis slowly shifts direction like a spinning top.

• This changes which hemisphere tilts more toward the Sun at different times.

• It affects the timing and intensity of seasons.

cosmic conditions for sustaining and propagating life

• good distance from galactic core

• orbit right type of star, and be at correct distance from that star

planetary conditions for sustaining and propagating life

• liquid water

• rocky planet

• chemical elements that are bioavailable

• magnetosphere and differentiated core

• energy source

• rotation rate allowing life

• axial inclination and elliptical orbit giving seasons

• big moon

what does venus lack?

• no strong magnetic field protecting from solar radiation

• extremely hot - strong greenhouse effect

• no liquid water

• not correct distance from sun

• different chemical composition of rocks and soils

• no geological and biological interactions providing essential nutrient cycles

• rotates very slowly

• no plate tectonics

• dense and toxic atmosphere, with high pressure

habitability

set of conditions necessary for the existence of life (even if it does not exist)

ex. a house

3 fundamental criteria for planetary habitability

1. source of energy

2. chemical elements needed for life (ex. C, N)

3. liquid water

the milkly way galaxy

• formed 13.6 billion years ago (Ga) - after the big bang

• grew from one or several small overdensities

• consists of 200-400 billion stars

• contains our solar system

galactic habitable zone

region within a galaxy where conditions are favourable for the emergence and sustenance of life

the planetary system must be:

• close enough to centre of galaxy to have enough heavy elements that favour formation of terrestrial planets

• far enough from centre to avoid: brushing of stars causing orbital instabilities or showers of comets and asteroids, supernova radiation, and large black holes of the galactic centre

formation of our solar system

1. 4.6 Ga there was collapse of gigantic cloud of dust and gas covered with ice from effect of its gravity, became swirling disk of matter,

2. formed protostar (presursor to sun) and protoplanetary disk (where planets grow out of)

3. got hotter and hotter, sun formed at centre via nuclear fusion (hydrogen → helium, began to shine)

4. the progressive agglomeration and accretion of dust resulted in planetesimals, and finally 8 planets and satellites

circumstellar habitable zone

region around a star (sun) where conditions are just right for liquid water to exist on a planet's surface — an essential factor for life

depends on:

1. radiative flux of the host star - depending on size, emits amount of energy

2. radius of the planets orbit - if too wide, might not have liquid water

3. mass of the planet

why is the sun ideal star for life?

• not too big

• has life of billions of years to allow evolution of life

• emits enough high-frequency UV to form ozone, but avoid ionization

• liquid water can exist on planets orbiting at a distance without gravitational locking

• constant/stable energy flux (varying from <0.1%)

why is earth an ideal planet for life?

• close enough to sun to accumulate heavy metal elements - formed solid surface (ie. terrestrial planet, not gas giant which is further out)

• big enough mass to maintain an atmosphere (due to gravity)

• geologically active for billions of years

• liquid core essential for generation of magnetic field - this protects surface from cosmic radiation and solar particles

how are earths orbital parameters good for life

• stable and circular rotation - allows little climate change

• rate of rotation allows for life (ie. not locked by tides with one face permanently facing star, not too fast so avoids large temperature contrast)

• moderate axial inclination - allows seasons and heat transmission

• large moon - allows stabile rotation, promotes tides, mixing of atmosphere and ocean

geological differentiation

process where earth is separated into layers of different compositions and densities

steps:

• partial melting: intense heat caused by impacts, radioactivity, and internal pressure caused materials to melt

• density separation: heavy elements (ex. iron and nickle) migrated towards centre forming core. lighter elements (ex. silicon and oxygen) ascend to form mantle and crust

  • this created geological layers - inner/outer core, mantle, crust

what does the active geosphere with tectonic plates on earth allow for?

1. chemical differentiation of the planet allowed for formation of continental and oceanic crusts. this geological diversity created different environments - biodiversity.

2. constant outgassing (release gases through volcanic outgassing) contributes to atmosphere and hydrosphere (needed for life)

3. nutrient recycling : tectonic plates are moving around, causing chemical elements necessary for biogeochemical cycles and life to be recycled, maintaining stable climate favourable for life

Earth’s Unique Orbital and Planetary Features

• Stable and nearly circular orbit: Prevents extreme climate shifts.

• Moderate axial tilt: Causes seasons, distributes heat.

• Fast rotation: Prevents extreme temperature contrasts.

• Large Moon: Stabilizes axial tilt, drives tides.

• Sufficient Mass: Retains an atmosphere, supports geological activity.

• Liquid Core: Generates a magnetic field that protects against solar radiation.

how is the formation of the core a key factor in habitability and presence of life?

• metals and radioactive elements: metallic elements (ex. iron, nicklel) and radioactive elements (ex. uranium) in core produce heat which fuels geological and tectonic activity

• creation of magnetic field: interactions between the inner core (solid) and outer core (liquid iron) creates geodynamo, generating magnetic field - this protects earth from solar winds and cosmic radiation, preserving atmosphere

how is the formation of earths crust and essential elements a key factor in habitability and presence of life?

availability of nutrients: the crust contains light elements (ex. silicon, oxygen, and carbon) and metals (ex. iron, calcium, and potassium) - these elements are needed for the chemistry of life, and allow for formation of first organic molecules and biodiversity

how is the formation of atmosphere and hydrosphere a key factor in habitability and presence of life?

• degassing: internal heat + volcanic activity released gases (CO2, H2O, N2) which formed atmosphere and hydrosphere

• greenhouse effect: greenhouse gases allowed atmosphere to retain enough heat to maintain temperature for liquid water

tectonic plates formation (and role in habitability of earth)

• 4.5 Ga: cooling led to formation of protocrust

• 3 Ga: crust cooled and thickened enough to form distinct plates

• plates float on the partially liquid mantle, moving around

  Outcome:

• several processes arose (ex. carbon cycle, volcanic outgassing, chemical weathering of rocks) stabilizing earths conditions

• constant recycling of essential elements, contributing to regulation of atmosphere and climate

• when plates collide and get stuck, creates supercontinents (ex. Rodinia, Pannotia, Pangea) —> continents are moving around, and depending where they are, heat is being distributed differently which drives climatic conditions

• movement of plates and formation geological masses influence biogeochemical cycles

anoxic atmosphere

4.5 billion years ago atmosphere had no oxygen. it was composed simply of volcanic gases ex. water vapour (no liquid water yet), carbon dioxide, hydrogen sulfide, methane and ammonia

liquid water

present approx 4.4 billion years ago, Earth's crust had stabilized and cooled sufficiently soon after its formation

zircons

provide evidence for the existence of liquid water on early Earth through their chemical composition and the conditions under which they formed:

• they form in a volcanic setting and are highly durable and can survive erosion. deposition is determined using U-Pb dating techniques → erosion and deposition require liquid water present

• zircons contain oxygen isotopes → enriched in oxygen 18 which is compatible with liquid water. oxygen isotope ratios in zircons indicate interaction between water and rock, suggesting the existence of fresh water on Earth's surface. findings imply the presence of continental crust above the ocean at that time.

where did water come from? 3 theories

1. water was brought by Theia: Mars sized planet that collided with Earth

2. water was present since formation of earth: H and O present in rocks, H₂O outgassing of young molten earth

3. water from collisions with comets and asteroids

what was the Miller and Urey “Primitive Soup Theory” experiment

experiment to replicate conditions of early earth to see if can get building blocks of life in another setting

• generate organic compounds from a “primitive soup”

results/conclusions of the Miller and Urey “Primitive Soup Theory” experiment

through abiotic processes, found accumulation of organic matter, amino acids → the building blocks of life

• thus, organic compounds (including amino acids) could be created from inorganic components under conditions similar to those on early earth.

• where? underwater volcanos, atmosphere, hydrothermal vents, tidal areas/cycles

redox reactions - how are they central part of cellular metabolism and drive cells?

chemical reaction where there is transfer of electrons between 2 substances (OILRIG)

1. generate energy - by moving electrons from 1 chemical to another

2. conserve energy - cells store energy (ATP) by coupling its synthesis to release of energy from redox reactions

   *the habitable earth has evolved due to these reactions during interactions between geosphere, atmosphere, hydrosphere, and biosphere - taken advantage of by life