Extinction – past and present
- We are living in an age of mass extinction
- The current extinction crisis has the highest recorded rate of speciesloss
- We therefore need to examine geological history to place this in context and understand why we face these problems
The age of bacteria
- Earth is 4.55 billion years old
- There has been life on earth for the last 3.8 billion
- Bacteria dominated for the first 3.1 billion of these!
The primitive atmosphere
- During this period the atmosphere comprised nitrogen, CO2, hydrogen and water vapour
- This environment created a primordial ‘soup’ where Prokaryotes developed a range metabolic adaptations
The Atmospheric revolution
- The arrival of cyanobacteria (2.6 Bn BP)
- The exhaustion of mechanisms for absorbing excess oxygen
- Atmospheric oxygen arrives..
- Mass extinction follows!
Biodiversity through time
- After this first global ‘catastrophe’ sees the rise of the Eukaryotes (which have mitochondria)
- Diversity gradually increases over time and explodes during the Cambrian epoch
- The rate of accumulation of diversity is not, however, constant…
- Rapid periods of diversification are followed by stable periods, punctuated by periods of mass extinction
We can understand the trajectory of past species diversity through the fossil record
- The first species explosion occurred during the Cambrian 600 million BP:100 phyla appeared of which 32 survive today
- 60 million years later another important diversification during the Paleozoic
- The last major event occured at the Cretaceous/Tertiary boundary (extinction of dinosaurs – rise of the mammals)
Five Mass Extinctions
- (500MA) Ordovician: 50% of animal families (e.g. trilobites)
- (350MA) Devonian: 30% of animal families (fish, trilobites)
- (250MA) Permian: 50% of animal families (95% marine life)
- (180MA) Triassic: 35% of animal families (reptiles, molluscs)
- (65MA) Cretaceous: dinosaurs, marine life
The rate of current extinction
- We are living during the sixth mass extinction event
- From the beginning of the Pleistocene era (2 million BP) increasingly drastic oscillations in global temperature (ice ages)
- However, large animal extinctions coincide much better with the arrival of Homo sapiens..
Well known recent examples: Pleistocene megafauna: Smilodon- sabre toothed cat, Giant ground sloth
Island species very badly affected (Giant birds)
The last 150 years..
- The known rate of extinction has soared
- We know this best through birds and mammals
- This rate of extinction is unprecedented
Other groups badly affected in the current wave:
- Coral (reef bleaching)
- Mass Amphibian extinctions
- Loss of molluscs from island systems
EXTINCT: Mammals (58), Birds (115), Molluscs (191), Other animals (120), Plants (517).
Species vulnerable to extinction
1. RARE SPECIES
• A species can be rare…