Conditions for life on Earth
how the main conditions which allowed early life to develop and survive, came about
features of earth that created (DAMMS) conditions for life
early conditions on earth that allowed life to develop
mass of the earth large enough - to prevent most essential ambient gases escaping. Liquid water is present - pressure prevents boiling
magnetosphere - molten layers underneath earth's crust produced a magnetic field. Deflects solar wind and prevents biologically damaging radiation reaching earth's surface
distance from the sun - earth in a Goldilocks zone. This means that insolation (controlled by surface albedo, absorption of IR energy and composition of atmosphere) provided the energy for photosynthesis and heat energy produced suitable temp for life and drives the water cycle. Liquid water is also present
axis of rotation - earth at an angle to its orbit around the sun. Produces seasonal variation. Reduce temp
speed of rotation - the time for the earth to rotate on its axis produced a day/night cycle. 24hr period of rotation reduces temp extremes.
presence of liquid water - is vital because: aquatic and marine environments, changes the wider environment, is the general physiological solvent, important in transport, key role in temp regulation, vapour is a greenhouse gas, high specific water capacity - helps moderate the rate and size of temperature changes, has an anomalous expansion on freezing, absorbs UV radiation
suitable temp - most areas have temps between 0 and 35 degrees C. Most areas are warm enough to have liquid water but not denature proteins
solar insolation - provided: 1. the heat energy produced by absorption of sunlight drives water cycle and produces suitable temps for life by warming the earth's surface and oceans. (if temp is too high or too low enzymes denature). 2. the energy for photosynthesis
atmospheric gases - the earth's atmosphere included three compounds (ammonia, carbon dioxide and methane). these form a total of four elements (nitrogen - needed for making protein, oxygen - needed for aerobic respiration and formation of high level stratospheric ozone which shields the earth from harmful UV radiation, carbon - needed for photosynthesis, regulates earth's temp, all life is carbon based and hydrogen - key component in water, regulates processes in living organisms, needed for photosynthesis, is present in methane which regulates earth's climate)
How the presence of life on earth has brought about environmental change. - life became more abundant - this started to change the environmental conditions - these new environmental conditions eventually made it possible for new life forms to evolve and new habitats to be colonised
how biota has helped to maintain stability
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
biogeochemical cycles - As a greater variety of organisms evolved, interconnected 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. They also prevent the build up of waste products
carbon sequestration - photosynthetic organisms (photoautotophs) reduced atmospheric CO2 concs. When they die the carbon that was part of their structure became carbonate rocks and fossil fuels. This reduction in atmospheric CO2 levels helped prevent a long term temp rise as the brightness of the sun increases about 10% every billion years.
ozone layer - once oxygen concs started to rise in the atmosphere, the O absorbed UV light - producing a dynamic equilibrium of chemical reactions involving O3, O2 and O in the stratosphere. This made life on earth's surface possible. O cons stopped building up about 540 million years ago. Many anaerobic archaea died out but animals and plants evolved.
oxygen production - oxygen was first produced by photosynthetic bacteria. For millions of years all the oxygen reacted with iron in oceans. The surplus then built up, oxygen then produced by algae. Concs started to rise in atmosphere. O produced by plants.
How historical conditions for life were monitored in the past and how these methods have developed over time
Limitations of early methods
Improved methods
reliance on proxy data - e.g. dendrochronology (info gained by natural recorders of climate variability), pollen records
lack of data collection - in many areas
lack of sophisticated equipment - for accurate measurements
limited coordination between researchers
limited reliability of proxy data for ancient conditions - e.g. pollen records. Vegetation is a good indicator of climate so changes in vegetation can be used to infer changes in climate. Pollen may be trapped in ice or bogs where it does not break down. A core sample of pollen can then provide history of the vegetation and climate. The deeper the sample the the further back in time. Limitation - pollen can travel a long way from its source.
inability to measure many factors
lack of ancient historical data - e.g. dendrochronology, with each year's growth, trees add an outside 'ring' to their body. The number of rings, the width of the rings and the chemistry may be evaluated. Scientists may be able to infer information such as available water, solar radiation and temperature. Limitation - cannot date further back than the age of trees
we have improved carriers for monitoring equipment, so we can collect more data from a wider range of areas
technological developments mean we have electronic measuring equipment
researchers around the world work together and share data and equipment e.g NOAA, AMDAR (aircraft)
collection of long term data sets
gas analysis of ice cores
isotope analysis of ice cores
the improved carriers for monitoring equipment involving helium balloons, aircraft and satelites
key principles
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