What is the Ecosphere

• The interactive zone on the surface of the earth where life can exist
• Extent - major part 200 m below the ocean surface and 6000m above sea level
• Driving forces - Energy from the Sun
• Material and energy cycling from the lithosphere,atmosphere and hydrosphere
• Life adapts to it and changes it by its presence

Chemical uniformity of Life

• All Life is made up of : C, H, O, N ( about 96% )
• other minor but essential elements needed for life

What is life: general characteristics of life

• Growth: by absorption of nutients and energy to build new cells
• Replication: to produce new off-spring
• Response to external stimuli: needed for evolution

The process of growth: Metabolism

• Anabolism: energy used to build complex molecules from simple ones, e.g., photosynthesis: conversion of solar energy and available materials to build complex molecules so life has an energy source to maintain its living functions
• Catabolism: energy release by breakdown of complex molecules when needed
• These can be described as below

Life’s molecules

• Amino acids: building blocks of life
• Proteins
• Enzymes: Proteins as catalysts to absorb energy and assemble new cells
• RNA and DNA for ordering the amino acids in all living matter
  • Nucleic acids - blue print for replication
  • Molecules of sugar, base and phosphates
    • source for sugars: polymerization of formaldehyde HCHO
    • source for bases: polymerization of HCN in primitive atmosphere
  • Phosphate: released from rocks by the action of HCN and Water to produce oxalic acid HOOC-COOH which dissolves phosphate
  • Lipids: form membranes

The Cell: the basic unit of life

• Nucleus: RNA, DNA , other proteins and enzymes
• Cell membrane : Fatty acids with hydrophilic COOH heads and long chains of CH2-CH2-CH3 etc which are hydrophobic
• Keeps the integrity of the cell from the surroundings

The basic functions of proteins

• Form all the tissues necesary for life - muscles, ligaments, hair and blood cells
• structues such as shells and bones
• as enzymes speed of reactions necessary for life by thousands to millions of times

Physical and chemical conditions necessary for origin of life

• Shielding from UV radiation
• Source materials: Liquid water, initial atmosphere with appropriate composition
• Conditions for assembly of organic molecules

The origin of life: chemosynthesis- the origin of simple life molecules, aminoacids from available inorganic material

• Chemosynthesis of life's molecules: The First step
  • Oparin’s ideas: early atmosphere of methane, ammonia, water vapor and H
  • Confirmation by Urey-Miller experiments for synthesis of aminoacids
    • Initial experiments with reducing gases: over 20 essential aminoacids
    • Later experiments with oxidizing gases, e.g. CO2, Water vapor and minor methane and ammonia
    • Yield of aminoacids is small but given enough time small amounts can be concentrated

Other possible sources

• Evidence from meteorites - Carbonaceous chondrites
• Organic matter composed of aminoacids, hydrocarbons , and fatty acids
• Interstellar clouds
• Panspermia? Or did it start in the earth
• Advantage of having lot more time for origin of life
• Disdavantage - thinness of space, radiation damage etc

Steps in the formation of life - A process, not an event

• inorganic production of simple organic molecules
• Concentration of these molecules in some environments

Biosynthesis: organization by polymerization of simple molcules to proteins

• self- assembly of organic molecules
• heating at 40-60 degrees produces long chains
• Fatty acids + phopshates dried at 40 degrees produce membranes
• Possibilities:
  • The role of clays
  • Inorganic reactions in black smokers in the oceans

The early oceans as dilute primordial organic soup

• Opportunities for concentration
• Wave action on lipids and enclosure of concentrated molecules
• Polymerization by sunlight

Early Life anaerobic : no free oxygen in the early atmosphere

The earliest life on earth- before the fossil record

• Archaebacteria - primitive single cells, anaeorobic, at 80-95 degrees C
• inorganic reactions for chemical energy
  • Hydrogen + Sulfur = Hydrogen Sulfide+ Energy
  • Carbon dioxide+ Hydrogen = methane+Water+ energy

The first fossil record of cells: 3.5 billion years ago

• Procaryotic - small and simple, no defined central nucleus, reproduce asexually, drive energy by fermentation of carbohydrates to alcohol and CO2
• Structures built of layers of calcium carbonate: similar to Australian stromatolites built today by blue green algae
• No oxgen present - sedimentary record of pyrite etc in old rocks
• aerobic procaryotes -the only lifeon the earth for nearly two billion years from 3.5 b.y begining to appearance of Eucaryotes at 1.4 b.y. ago
• living and fossil procaryotes are bacteria

Adaptation of prokaryotic cells to photosynthesis: cyanobacteria

• single-celled organisms like modern blue-green algae
• Release of free oxygen

Eucaryotic cells on the scene at 1.4 b.y ago

• By agglomeration of primitive procaryotic cells each carrying out a single function
• Eucaryotes are aerobic: can use Oxygen for breakdown of carbohydrates
• Evolution to eukaryotes: into plants and animals

Consequences of the production of free oxygen

• Oxidation of iron
• Formation of stromatolites
• Banded iron formations as early as 3.5 b.y ago
• Free oxygen into the atmosphere
• Expansion of the Eukaryotes into plants and animals

The appearance of free oxygen in the atmopshere - ~1.5 b.y. ago

• Presence of Pyrite in older sediments
• Banded Iron Formations (BIF’s) -oxygen sinks in the early earth
• Production of natural ozone shield against UV - life on land

Summary chronology of the record of life on earth

• ~4.0 b.y ago - first appearance of primitive cells
• ~3.5 b.y. ago first fossils of primitive cells
• 3.5 -2.5 b.y. ago production of Oxygen by photosynthetic procaryotes
• ~2.5 b.y. ago abundant stromatolites
• 1.5 b.y ago - first appearnce of eucaryotes, free oxygen in the atmosphere
• ~ 600 m.y. ago evolution of multicellur organisms- Ediacaran Fauna

Energy use of the biosphere

• Most of the incoming radiation is converted to heat
• Less than 1% of incoming solar radiation is fixed by the biosphere