The Living Environment (A2); The Conditions For Life On Earth (Complete)

Question 1

When was the Earth formed?

Answer 1

4.6 billion years ago

Question 2

How was the Earth formed?

Answer 2

-Gravity pulled rock fragments in space together
-Huge # of energy absorbed as rocks joined created heat & produced ball of molten rock
-Surface gradually cooled to produce a surface crust of solid rock

Question 3

What did the physical features of Earth make it suitable for?

Answer 3

Eventual development of life by controlling abiotic factors needed by living organisms

Question 4

How did Earth’s mass create suitable conditions for life?

Answer 4

-Was great enough to prevent most gases from escaping → space
-Atmosphere included elements essential for life like carbon, hydrogen, oxygen & nitrogen; present in compounds like methane, ammonia & CO2
-Atmospheric pressure was ↑ enough to prevent all liquid water from boiling; vital for living organisms as is general physiological solvent in which most biological reactions occur + important for transport & temp regulation

Question 5

How did Earth’s distance from the sun create suitable conditions for life?

Answer 5

-Light emitted from the sun & distance from it were suitable to produce temps on Earth suitable for life
-Being too close/for away would prevent liquid water being present
-Time taken for Earth to rotate on its axis produced day/night cycle fast enough to minimise excessive heating/cooling

Question 6

How did Earth’s axis of rotation create suitable conditions for life?

Answer 6

At an angle to its orbit around Sun which produces seasonal variations in conditions as Earth orbits Sun

Question 7

How did Earth’s speed of rotation create suitable conditions for life?

Answer 7

-Temp of Earth’s surface ↑ when is exposed to sunlight & falls when isn’t
-24h period of rotation of Earth around its axis ↓ temp extremes

Question 8

How did Earth’s magnetic field create suitable conditions for life?

Answer 8

Molten layers beneath crust produce Earth’s magnetic field that deflects ‘Solar wind’, prevents biologically damaging radiation reaching Earth’s surface

Question 9

When did life first develop on Earth?

Answer 9

About 3.5 billion years ago

Question 10

How were the conditions on Earth different when life first developed compared to now?

Answer 10

-Atmosphere contained same toxic gases like ammonia but no oxygen
-Solar energy reaching ground included high levels of UV radiation
-Chemical composition of sea included increasing complex organic molecules

Question 11

How did life develop on Earth?

Answer 11

-Simple single-cells eventually formed, possibly around volcanic geothermal vents on seabed where warm temps & rich mix of chemicals made biological processes more likely
-These Archaea were single-celled organisms similar to bacteria → still survive in many habitats, especially oceans. Some are anaerobic like methanoganic archaea in intestines

Question 12

How did the presence of liquid water & its features allow Earth to develop life?

Answer 12

-Solvent water; ‘general physiological solvent’ most chemical reactions in living organisms involve reactants dissolved in water
-Transport within organisms; water= solvent in blood & sap where it transports dissolved gases, sugars, amino acids, mineral nutrients, waste
-Temp control; evaporation of water absorbs heat, causing temps to ↓
-Anomalous expansion on freezing; water= most dense at 4°C so cooler water than this floats, stopping convection current that may’ve cooled whole water body
-High specific heat capacity; water warms up & cools slowly, helps moderate rate + size of temp changes
-Aquatic habitats; oceans, seas, lakes, marshes, rivers
-Absorption of UV radiation; protected living organisms in oceans before ozone layer developed which absorbed UV in stratosphere

Question 13

How did the temperature range on Earth allow life to develop?

Answer 13

Most areas on Earth → 0°C & 35°C so most areas are warm enough to have liquid water but not hot enough to denature proteins

Question 14

How did atmospheric gases allow life to develop on Earth?

Answer 14

-CO2 for photosynthesis & synthesis of carbohydrates, proteins, lipids
-Nitrogen for proteins synthesis

Question 15

How did solar insolation allow life to develop on Earth?

Answer 15

-Sunlight → energy for photosynthesis
-Heat produced by absorption of sunlight provides energy driving water cycles & warming Earth’s surface & oceans
-# of sunlight absorbed by Earth’s surface depends upon albedo of surface
-Composition of atmosphere controls # of infrared energy absorbed & converted to heat

Question 16

How did atmospheric oxygen develop and how did this develop life & cause environmental change?

Answer 16

-By 2.7b years ago some archaea in oceans developed ability to photosynthesise & release oxygen
-For millions of years, all oxygen produced reacted w/ iron in oceans. Once all the iron had reacted w/oxygen, surplus dissolved oxygen built up in the oceans → much released into atmosphere where concentrations started to rise about 2.45b years ago
-Oxygen in atmosphere absorbed UV light, producing dynamic equilibrium of reactions involving O3, O2 & O
-Absorption of UV light made life on Earth’s surface possible
-Time period when oxygen in atmosphere was building up lasted until about 540m years ago, called the Proterozoic
-Many anaerobic archaea & bacteria died out but more complex aerobic organisms evolved including animals & plants

Question 17

How did carbon sequestration occur on early Earth and how did this cause environmental change?

Answer 17

-CO2= greenhouse gas, helps to retain heat energy in atmosphere -Photosynthetic organisms, photoautotrophs absorbed CO2; some of which was stored in geological sediments like carbonate rocks & fossil fuels
-↓ in atmospheric CO2 levels helped to prevent long-term temp rise even though brightness of Sun ↑ about 10% every billion years

Question 18

How were biogeochemical cycles produced on early Earth and how did this cause environmental change?

Answer 18

-As greater variety of organisms evolved, inner-connected biological processes developed → produced biogeochemical cycles
-Meant that relatively small # of some nutrient elements could support life over long periods of time w/out resources becoming depleted

Question 19

How did transpiration on early Earth cause environmental change?

Answer 19

Once plants had evolved & colonised land, transpiration returned water vapour → atmosphere,↑# of rainfall in other areas, making growth of even more plant life possible

Question 20

What data is used to research past conditions on Earth and why?

Answer 20

Proxy data, as direct measurements can’t be taken

Question 21

What are examples of new analytical techniques used to estimate past climate?

Answer 21

-Radioisotope composition can be used to date samples like the ratio of carbon-12 to carbon-14
-Ratio of oxygen-18 to oxygen-16 can be used to estimate past temps
-Composition of past atmosphere can be analysed from air bubbles collected from ice cores
-Ratio of magnesium to calcium in calcite deposits can be used to estimate the temp. More magnesium is incorporated at higher temps