G3 Climate and Life

• Early Earth

  • Very hot
  • No free oxygen
  • No oceans, lakes or rivers
  • High atmospheric pressure
  • 4.3 - 3.8 Ga was a period of intense comet and asteroid bombardment
• Precambrian Life

  • Earliest fossil is 3.55 Ga but chemical signatures of biological origin have been dated to older rocks
  • Stromatolites 3.8 Ga - formed by a growth of layer upon layer of photosynthetic bacteria
  • Banded Iron Formations appear at around 3.7 Ga and they indicate that the great oxygenation event was at 2.4 Ga
  • Eukaryotes appear around 1.8Ga
  • Ediacaran fauna appear around 565 Ma
• Cambrian Explosion

  • Explosion of life in the early Cambrian
  • Most major phyla appear during this time
  • Major diversification of life
  • Hard parts appear
• Factors causing the Cambrian Explosion

  • Oxygen levels - increase in oxygen levels lead to an increase in size, ozone filtered out harmful UV rays allowing complex life
  • CaCO3 Concentration - increase in CaCO3 provided material for hard parts
  • Predation - created selection pressures and also caused eyes and burrowing behaviour
  • Rise in sea level provided more ecospace
  • Hard parts - more efficient predation, protection for prey, efficient movement and stronger body for protection against currents
  • Preservation bias - appearance of hard parts increases chance of preservation - may not be real
• Evidence for the Cambrian Explosion

  • Almost every phylum known appears in the Cambrian
  • Trace fossils - show an increased diversity in Cambrian rocks and development of new ecological niches and strategies
• Why did hard parts evolve?

  • Protection from predators
  • Mineralised mouth parts for eating
  • To facilitate movement and exploration of new environments
  • Protection from the environment
  • Support structures for soft tissue allowing larger sizes
• Ordovician Radiation

  • Ecosystems increased in complexity
  • Fauna emerging in the Ordovician set the template for the rest of the Palaeozoic
  • Ordovician adaptive radiation - increase in diversity, particularly in filter feeding organisms
• Explain what is meant by the term Cambrian Explosion

  The sudden appearance of hard parts and organisms such as trilobites and brachiopods. It was an increase in diversity of species and fossils.
• A increase in chemical weathering releases calcium carbonate for use in hard parts of organisms. Chemical weathering adds more nutrients into oceans allowing more metabolic processes/building bigger bodies
• Glaciations/meteorite impacts lead to mass extinctions


  Rapid and dramatic environmental catastrophes allow for subsequent rapid diversification of life due to innovation and development of new animal groups and competition and selective processes following obliteration of previous ecosystems
• Suggest why it is difficult to reconstruct ecosystems occurring in the Precambrian

  It was a long time ago - greater chance for metamorphism, weathering or erosion which may have destroyed fossils. There were no hard parts then, meaning preservation potential was low. Furthermore, there are no living forms present today meaning we cannot apply uniformitarianism, and the diversity of life was low meaning the chance of being preserved was lower
• The Rise of Tetrapods

  • Tetrapod - four limbed animal containing extinct and extant amphibians, reptiles, synapsids (incl. mammals) etc
  • Amphibians - tetrapods with lifestyles in and out of water. Evolved from lobe-finned fish in the late devonian to early carboniferous.
  • Lobe finned fish - four fleshy fins supported by a bone in a similar structure to a hand
  • Tiktaalik - fossil intermediate between fish and tetrapods - specimens are extremely well preserved allowing detailed comparisons between lobe finned fish and early amphibians
• Lobe finned fish to early amphibians - differences

  • Development of skeletal girdle connecting limb bones to the skeleton for better movement on land
  • More robust skeleton strengthening vertebral column and rib bones - extra support on land
  • Eyelids formed to keep eyes moist as no longer submerged in water
  • Development of a double circulatory system
  • Tongue formed within its mouth to catch prey
  • Ears to detect sound waves through the air
  • Slender skull
• Evolution on land

  • Amniotic egg - provided protection whilst remaining porous allowing diffusion of gases into and out of egg (respiration)
  • Yolk sac and albumin - Yolk sac - food, albumin - water nutrients
  • Amnion - fluid filled sac around embryo
  • Amniotic egg allowed amniotes to move away from bodies of water and become larger
• Rise of dinosaurs and mammals

  • Dinosaurs evolved from archosaurs - after permio-triassic mass extinction
  • Birds are throught to have evolved from theropod dinosaurs in the late Jurassic. Similarities between dinosaurs and birds include:
  • Hollow thin-walled bones
  • S shaped curved neck
  • Elongated arms and forelimbs
  • Pubis shifted from anterior (forward position) to a posterior (backward position)
  • Large eye sockets in the skull
  • Hinged ankles to reduce rotation
• Archaeopteryx

  • Semi arboreal animal
  • Capable of gliding and sustaining flight
  • Shows characteristics of dinosaurs AND birds
• Feathers

  • Earliest preserved feathers are found in the late Jurassic
  • Feathers evolved to be more complex, becoming elongate and symmetrical
• Mammals

  • 225 Ma mammals and dinosaurs appear in the rock record
  • Many mammals lived in burrows and were nocturnal
  • During the mesozoic mammals yielded a vast array of body forms
  • Land mammals kept getting larger for 35Ma after the dinosaurs were wiped off the planet
  • Homosapiens appear around 300Ka
• Characteristics of a Mass Extinction

  • Large drop in diversity
  • High number of extinctions at the same time
  • Extinction rate is higher than origination rate
  • Wide variety of groups affected
  • Geographically widespread
  • Short time span
  • Sharp recovery - new fauna fills available ecospace
  • Fern spike common on land
• How can extinctions be selective?

  • Size
  • Abundance
  • Distribution
  • Specialisation
  • Adaptability
  • Morphology and mode of life
• Cretaceous - Palaeogene

  • 17% of families, 50% genera, 75% of all species
  • Non-avian dinosaurs and ammonites extinct
  • Echinoids, bivalves and fish severely affected
  • Mammals, birds, crocodiles survive
  • Mammals and birds radiate
• Evidence for the K-Pg Mass Extinction caused by meteorite

  • Iridium - layer concentrated at K-T boundary and most iridium comes from space
  • Shocked quartz forms under intense pressure and is associated with meteorite craters
  • Tektites - gravel sized glass formed from melting of soil and rock
  • Sedimentary evidence suggests a large Tsunami reached Texas
  • Chicxulub impact crater dated 65Ma
  • Deccan traps - widespread flood basalts in India. Millions of tons of sulphur dioxide
• Consequences of meteorite impact (K-Pg extinction)

  • Would have thrown up dust into the atmosphere as well as releasing sulphur dioxide
  • Resulting in widespread cooling + acid rain
  • Resulting in the collapse of life and the rest of the food chain
  • Fern spike due to being able to tolerate acidic conditions.
• Permian - Triassic

  • 57% families, 83% genera, 95% marine species
  • Trilobites, rugose and tabulate corals extinct
  • Most brachiopods extinct
  • Ammonoids and echinoids severely affected
  • Land reptiles and many trees extinct
• Evidence for the P-T mass extinction

  • Sedimentary evidence - widespread deposition of black shales and iron pyrite suggesting marine anoxia
  • Tectonic - Pangaea provided opportunity for glaciers to form.
  • Shocked quartz - found in Australia and Antarctica. However recently refuted suggesting that it is due to plastic deformation associated with tectonic activity
  • Meteorite impact crater - Several impact sites been suggested but later refuted.
  • Siberian traps - largest flood basalt provinces on Earth - time interval of around 900K years. Worldwide atmospheric contamination.
• Macroevolution and the tree of life

  • Life on earth is extremely varied - genetic and morphological data suggests all life on Earth is related
  • Tree of life shows phylogeny of organisms
  • Large trends and transformations in evolution above the species level is termed macroevolution
  • Evolution is: descent with modification OR genetics + time
• Phyletic Gradualism

  • Traditional view of evolution
  • Gradual change
  • Slow, steady divergence of lineages
  • Many transition forms are not preserved which makes evolution appear faster
• Punctuated equlibrium

  • Long periods of stasis/stability
  • A large amount of change in a short time, tied to a speciation event
  • Transitional forms exist for a short period
  • Evidence for punctuated equlibrium - variation in the number of eye lenses of the trilobite genus
  • More evidence for punctuated equilibrium includes:
  • Cambrian explosion/radiation
  • Radiation of mammals
  • Living fossils such as nautilus
• Cladistics

  • Aims to show evolutionary relationships based on physical traits shared by different groups of organisms
• Climate

  • Sum of weather conditions in a region over a long time, including variation in temperature, humidity, atmospheric pressure, wind and precipitation
  • Tilt of the Earth results in seasonality
• Gulf stream - long stream of warm surface water that keeps Europe warm and north America cold. Partly caused by circulation of ocean waters but mainly driven by winds
• Global circulation model - cooling effects around the globe driven by wind. Main source of heat is energy from short wave light from the sun. Heat comes from light absorbed from Earth’s surface re-emitted as long wave radiation, heating the air around it. Excess of heat at the equator and deficit at the poles due to the amount of sunlight hitting them (more at equator, less at poles).
• Ocean current circulation - driven by wind, tides, changes in water density and rotation of the earth. Modified by topography of ocean floor. Surface currents control motion of top 10% of ocean’s water. Deep ocean currents control other 90%.
• What causes climate change?

  • Changes in atmospheric composition of greenhouse gases
  • greenhouse effect - Atmosphere traps sun’s energy - EM radiation in broad range of wavelengths. Rock, soil and water reemit energy as heat.
  • Carbon dioxide, methane, water vapour, nitrous oxide - absorb IR radiation and re-emit. Not much escaping radiation leaves without encountering greenhouse gases. Greenhouse gases maintain the average surface temperature by retaining heat energy.
  • Volcanic activity, methane hydrates and chemical weathering all influence atmospheric greenhouse gas composition
• What causes climate change?

  • Distribution of the continents
  • Determines route of global current systems and strength of oceanic heat exchange between poles and equator. Movement of continents determines long term global climate
  • The carboniferous period - near continuous continental landmass extending from North to South poles.
  • Late carboniferous icehouse - development of ice sheets occurred due to:
  • Circulation of polar and tropical waters restricted by landmasses
  • Uplift = mountain belts disrupted atmospheric circulation
  • Air can be deflected and cooled by mountains
• Geological Carbon Cycle

  1. Carbon released into atmosphere by volcanism
  2. CO2 combines with rain to form carbonic acid
  3. Carbonic acid reacts with silicate rocks to give carbonates/ carbonic acid
  4. Washed into sea via rivers
  5. Used to form animal hard parts (calcium carbonate)
  6. Animals die and their hard parts form carbonate rocks
  7. Subduction of limestone, partially melted and eventually blasted out of volcanoes
• • Earth’s changing climate can be described as fluctuating through two distinct phases
  • Icehouse - lower temperatures, ice caps and glaciers, increased albedo
  • Glacial period - intervals with colder temperatures and expanding glaciers
  • Interglacial period - warmer intervals lasting thousands of years
  • Greenhouse - higher temperatures, lack of ice coverage, increase in insolation and greenhouse gases and lowered albedo
• Anthropocene

  • What is needed to recognise geologic units?
  • Palaeontological evidence - biological markers
  • Marker beds
  • Climatological or environmental changes
  • Other changes in the rock record
• • Applied to the Anthropocene:
  • Marker beds - nuclear weapons testing released plutonium-239 with a half life of 24,400 years
  • Biological changes - significant reduction in diversity and new fauna e.g. chicken bones. Agriculture.
  • Environmental changes - temperature rise, increase in atmospheric greenhouse gases, sea level rise etc
• • Issues with the Anthropocene
  • No significant rock horizons that occur globally
  • We may be in a transition period
  • Where do we draw the line? Is there enough evidence right now for the Anthropocene