OCR 1a Conditions for Life on Earth PDF

1a Conditions for life on Earth Spec Topic Subtopics Ref 3.1.1.1 How the main Atmosphere conditions, which Insolation allowed early life to Position in the solar develop and survive on system...

1a Conditions for life on Earth Spec Topic Subtopics Ref 3.1.1.1 How the main Atmosphere conditions, which Insolation allowed early life to Position in the solar develop and survive on system planet Earth, came Orbital behaviour about Magnetosphere 3.1.1.2 How the presence of Oxygen production life on Earth has Ozone layer brought about Carbon sequestration environmental change Biogeochemical cycles 3.1.1.3 How historical Limitations of early conditions for life were methods monitored in the past Improved methods and how these methods have been developed over time Content summary Conditions for the development of early life on Earth Atmosphere Mass of Earth and the force of gravity retain an atmosphere Gases are resources: Gases were present in the atmosphere and dissolved in the oceans (where life began) Carbon A source of carbon to make organic molecules: carbohydrates, dioxide proteins, lipids Methane A source of carbon and energy for metabolism Nitrogen For protein synthesis Atmospheric pressure Solvent for biological reactions and temperature Water’s high heat capacity reduces temperature fluctuations maintained liquid water The anomalous expansion of water as it freezes stops convection currents (when cooled from the air above) so only the surface layer freezes. Absorbed UV light protecting life in deeper water (until the ozone layer formed) Insolation Temperature range Sunlight was a major source of the energy that warmed the Earth: controlled by insolation - Absorbed by the Earth’s surface (especially if the albedo is low – low and atmospheric reflectivity) processes. - Re-emitted by the Earth as infrared and absorbed by atmospheric gases (CO2, Roles of: albedo, CH4) absorption of infrared energy and atmospheric gases Position in the solar system Temperature controlled Distance affects the intensity of insolation by distance from the If too close – too hot for liquid water Sun If too far away – too cold for liquid water Distances where life would be possible 100m – 250m km from the Sun (the ‘Goldilocks zone’) Orbital behaviour Rotation and tilt on its Rotation is fast enough that there is not excessive heating during the day or axis and orbit around cooling at night. the Sun control daily The tilt on its axis produces seasonal variations in temperature and insolation. and seasonal variations in insolation and temperatures Magnetosphere Molten core produces a Convection currents in the molten outer core create electric currents and a magnetic field magnetic field (magnetosphere) deflects harmful solar radiation How the presence of life has caused environmental change Oxygen production First by photosynthetic The early atmosphere contained virtually no oxygen. bacteria, then by algae and Oxygen released by photosynthesis was removed by reactions with dissolved plants iron in the oceans, forming Proterozoic iron sediments (approx. 2.45b years ago). After this, free oxygen was released into the atmosphere, where concentrations increased. Formation of the ozone layer By chemical reactions O2 that built up in the atmosphere absorbed UV light from the Sun. O2 split, involving oxygen and producing monatomic O, which reacted to produce O3 ultraviolet light Carbon sequestration Storage of carbon from Some of the carbon captured by photosynthesis entered long-term carbon dioxide by lithosphere stores such as fossil fuels and carbonate rocks (limestone, chalk). photoautotrophs This reduced atmospheric CO2 levels and prevented excessive temperature rise as the energy output of the Sun increased (10% per billion years) Development of biogeochemical cycles Cycles are linked by living Living organisms are involved in all biogeochemical cycles, maintaining linked organisms, preventing the dynamic equilibria. build-up of wastes or resource depletion How historical conditions for life were monitored in the past and how these methods have been developed over time Limitations of early methods. Lack of ancient historical data. Limited reliability of proxy data for Proxy data can be inaccurate as many variables, that can’t be ancient conditions measured, may have influenced the data eg dendrochronology, pollen analysis. Limited coordination between Lack of rapid communications made data sharing more difficult researchers. Inability to measure many factors. Many monitoring technologies have only been developed recently. Lack of sophisticated equipment for Early equipment was often simple, inaccurate and not standardised. accurate measurements. Lack of data collection in many areas. Researchers were not evenly distributed around the world. Improved methods. Collection of long-term These make analysis of trends and fluctuations easier data sets. The use of electronic Data may be collected: monitoring equipment. - more frequently - without the need for human presence - in more remote/widely dispersed areas Data may be more accurate and standardised Gas analysis of ice Gas concentrations cores. CO2 concentrations are used in long-term analysis of climate change Isotope analysis The ratio of oxygen16 to oxygen18 allows estimation of past temperatures. Levels of beryllium10 indicate past solar activity. Peaks of beryllium10 can be used to date-match data from different ice cores Improved carriers for These allow the collection of: monitoring equipment, - continual/frequent data sets eg helium balloons, - data over larger areas aircraft, satellites. - data higher in the atmosphere/in locations where it is impractical to have human researchers Key Terminology Term Definition A measure of the reflectivity of a surface. More reflective surfaces have high albedos. A surface that reflects all light has an albedo of 100%, Albedo while one that absorbs all light has an albedo of 0%. The albedo of an area can affect the local climate. Microorganisms similar to bacteria, including the first life-forms to Archaea develop on Earth. Archaea are the only organisms that produce methane from the decomposition of organic matter. The gases surrounding the Earth. Different layers are characterised by Atmosphere their temperature, density, turbulence and composition. A series of linked processes which use and re-use elements such as Biogeochemical carbon, nitrogen, phosphorus, iron and sulfur, as they move between cycle biotic and abiotic reservoirs. Carbon Any process which removes carbon dioxide from the atmosphere, such sequestration as afforestation or underground storage (carbon capture). The method of determining the age of a piece of wood using the Dendrochronology characteristic sequence of sizes of growth rings in the wood. The magnetic field around Earth which deflects charged particles Magnetosphere travelling from the Sun. An organism that produces high-energy food substances using sunlight Photoautotroph in photosynthesis. The use of the pollen present in environmental samples. This can be Pollen analysis used to deduce the climate when historic sediments were deposited. The use of data that can be collected to predict the values of a related factor that cannot be measured, eg data on tree rings, pollen, coral Proxy data growth and plankton in marine sediments can be used to determine historic climates. Earth before life The Earth was formed about 4.6 billion years ago as gravity pulled rock fragments in space together. The huge amount of energy absorbed as the rocks joined, created heat and produced a ball of molten rock. The surface gradually cooled to produce a surface crust of solid rock. The physical features of Earth made it suitable for the eventual development. of life by controlling the abiotic factors. that are needed by living organisms. Features of Earth that created suitable conditions for life A range of features of the structure, position and behaviour of Earth made the development of life possible. Mass The mass of the Earth was great enough to prevent most gases from escaping into space. This atmosphere included the elements essential for life: carbon, hydrogen, oxygen, and nitrogen. They were present in compounds such as methane, ammonia, and carbon dioxide. The atmospheric pressure was high enough to prevent all the liquid water from boiling. Water is vital for living organisms as it is the general physiological solvent in which most biological reactions take place. It is also important in transport and temperature regulation. Distance from the Sun The light emitted from the Sun and the distance from the Sun were s produce temperatures on Earth that would be suitable for life. Being too close or too far away from the Sun would prevent liquid water being present. The time taken for the Earth to rotate on its axis produced a day/night cycle that was fast enough to minimise excessive heating or cooling. Axis of rotation The axis of rotation is at an angle to its orbit around the Sun which produces seasonal variations in conditions as the Earth orbits the Sun. Speed of rotation The temperature of the Earth's surface rises when it is exposed to sunlight and falls when it is not. The 24-hour period of rotation of Earth around its axis reduces temperature extremes. Magnetic field The molten layers beneath the crust produce the Earth's magnetic field that deflects the 'solar wind' and prevents biologically damaging radiation reaching the Earth's surface. Life first developed on Earth about 3.5 billion years ago. The conditions on Earth then were very different from those that exist now. The atmosphere contained some toxic gases, ammonia, but no oxygen. The solar energy reaching the ground included high levels of ultra- violet radiation. The chemical composition of the sea included increasingly complex organic molecules. Development of life on Earth Eventually, simple single-cells formed, possibly around volcanic geothermal vents on the seabed where the warm temperatures and rich mix of chemicals made biological processes more likely. These Archaea were single-celled organisms similar to bacteria. They still survive in many habitats, especially the oceans. Some are anaerobic, such as the methanogenic archaea that live in intestines and marshes. Early conditions on Earth that allowed life to develop After the formation of the Earth about 4.6b years ago, the conditions changed, eventually becoming suitable for life to develop. Presence of liquid water All living organisms require water for survival. It performs essential physiological functions and controls many environmental conditions. Solvent water: the 'general physiological solvent. Most chemical reactions in living organisms involve reactants that are dissolved in water. Transport within organisms: water is the solvent in blood and sap where it transports dissolved gases, sugars, amino acids, mineral nutrients, waste products. Temperature control: the evaporation of water absorbs heat, causing temperatures to decline. Anomalous expansion on freezing: water is most dense at 4°C so water that is cooler than this floats, stopping the convection current that may have cooled the whole water body. High specific heat capacity: water warms up and cools down slowly, which helps to moderate the rate and size of temperature changes. Aquatic habitats: oceans, seas, lakes, marshes, and rivers. Absorption of UV radiation: this protected living organisms in the oceans before the ozone layer developed which absorbed UV in the stratosphere. Temperature range Most areas of Earth have temperatures between 0°C and 35°C, so most areas are warm enough to have liquid water but not hot enough to denature proteins. Atmospheric gases  Carbon dioxide for photosynthesis and the synthesis of carbohydrates, proteins, and lipids. Nitrogen for protein synthesis. Solar insolation Sunlight provides the energy for photosynthesis. The heat produced by the absorption of sunlight provides the energy that drives the water cycle and warms the Earth's surface and the oceans. The amount of sunlight that is absorbed by the Earth's surface depends upon the albedo of the surface. The composition of the atmosphere controls the amount of infrared energy that is absorbed and converted to heat. How life on Earth caused environmental change As life developed and became more abundant, it started to change the environmental conditions which eventually made it possible for new life forms to evolve and new habitats to be colonised. Atmospheric oxygen By 2.7 billion years ago, some of the Archaea in the oceans had developed the ability to photosynthesise and release oxygen. For millions of years, all the oxygen produced reacted with iron in the oceans. Once all the iron had reacted with oxygen, the surplus dissolved oxygen built up in the oceans. Much of this was released into the atmosphere where concentrations started to rise about 2.45 billion years ago. Oxygen in the atmosphere absorbed ultra-violet light, producing a dynamic equilibrium of reactions involving O3, O2, and O. The absorption of ultra- violet light made life on the Earth's surface possible. The time period when oxygen in the atmosphere was building up lasted until about 540m years ago and was called the Proterozoic. Many anaerobic Archaea and bacteria died out but more complex aerobic organisms evolved including animals and plants. Carbon sequestration Carbon dioxide is a greenhouse gas and helps to retain heat energy in the atmosphere. Photosynthetic organisms, photoautotrophs, absorbed carbon dioxide, some of which was stored in geological sediments such as carbonate rocks and fossil fuels. This reduction in atmospheric carbon dioxide levels helped to prevent a long-term temperature rise even though the brightness of the Sun increases by about ten per cent every billion years. Biogeochemical cycles As a greater variety of organisms evolved, inter-connected biological processes developed which produced biogeochemical cycles. These meant that relatively small amounts of some nutrient elements could support life over long periods of time without the resources becoming depleted. Transpiration Once plants had evolved and colonised the land, transpiration returned water vapour to the atmosphere and increased the amount of rainfall in other areas, making the growth of even more plant life possible. The development of methods to research past conditions on Earth Detailed, comprehensive, scientific knowledge of the planet and its past has developed relatively recently. Proxy data is often used as direct measurements of past conditions cannot be taken. This requires an understanding of how natural systems work and the development of new analytical techniques. Increasing understanding of continental drift, ocean currents, ocean chemistry and atmospheric processes have been very important in understanding why and how conditions changed. New analytical techniques have been developed that can be used to estimate past climate, for example: radioisotope composition can be used to date samples such as the ratio of carbon-12 to carbon-14; the ratio of oxygen-18 to oxygen-16 can be used to estimate past temperatures; the composition of past atmosphere can be analysed from air bubbles collected from ice cores; the ratio of magnesium to calcium in calcite deposits can be used to estimate the temperature. More magnesium is incorporated at higher temperatures. More details of monitoring techniques can be found in other topics, for example, global climate change and research methods. Big picture The structure and movement of Earth, and its position in the Solar System, control the abiotic conditions on Earth that make life possible. The presence of life has changed the conditions on Earth and made it more suitable for life to become more varied and abundant. Living systems have responded to environmental changes, such as the increasing intensity of sunlight. This has maintained the conditions that allow living organisms to survive.