balance of matter + energy exchange

productivity

rate which producers capture + store energy within organic compounds

• rate, NOT total

how is productivity measured?

• energy per unit area (J/m2/a)

• biomass of vegetation added per area (g/m2/a)

what two factors control the amount of productivity an area will have?

• solar energy

• moisture

homeostasis

Maintaining a state of equilibrium

what plays a vital role in maintaining homeostasis in the biosphere, and why?

living organisms

• there would be more CO2 and salt in the world if not for them

what can give us clues about the composition of earth’s atmosphere and water in the past?

Deposits of ancient micro-organisms

what was earth like 3.8 billion years ago, and what organisms were present?

atmosphere lacked free oxygen

• bacteria lived in shallow seas + lakes

stromatolites

sedimentary rocks created by dead bacteria cells

what did bands of iron oxides signify in stromatolites?

that there was oxygen in a body of water

• made bc iron stromatolites in the water combined w water to create iron oxide

how old are stromatolites with (black) iron oxide bands, and what does it mean?

2.5 billion years, this was likely when oxygen began to flow in our world

how old are stromatolites without iron oxide bands

less than 1.8 billion years

why were there no black bands on stromatolites 1.8 billion years ago?

• most of the iron ions in the oceans were already bound as iron oxides.

• since the water had no more iron, oxygen from photosynthesis built up + escaped

what caused a sudden increase in oxygen 2.5 billion years ago

activity of photosynthetic cyanobacteria.

what did microorganisms rely on at the time in order to get the nutrients they needed?

anaerobic respiration