Lecture 1: The Biodiversity Crisis: Science and Understanding 4

Question 1

Garden of eden

Answer 1

For many years scientists believed that all life on Earth was dependent directly on the sun – primary producers (cyanobacteria, algae, plants etc.) use sunlight as an energy source to convert carbon dioxide and water into sugar (mainly carbohydrates)
and so form biomass, which is then consumed by higher members of the food chain

• It therefore made sense to consider that life would have originated somewhere which would have had ready access to sunlight as a form of energy, in an organic- rich medium which would have helped to catalyse chemical reactions, such as water and clay – leading to the ‘primordial soup’ theory

Question 2

Life in the ocean depths

Answer 2

In the 1970s the Galapagos Rift in the Pacific Ocean (2.5 km deep) was explored as geologists looked at black smokers

It was known that some animal communities lived at this depth, feeding on detritus from above

Question 3

More on ocean depth

Answer 3

What the scientists were amazed to find were thermophilic bacteria living right next to the black smokers where the temperatures were as high as 110oC (most proteins break down at around 50oC, leading to the death of an organism)
• Even more significant was the fact that these bacteria (primary producers) were living where no sunlight could reach – they were autotrophs, obtaining all their energy from the chemicals (e.g. sulphur) spewing from the volcanic vents
• This means that abiogenesis did not necessarily need sunlight to occur, and may not have occurred on the surface at all

Question 4

Ascent from hades

Answer 4

In the 1980s scientists began to search for evidence of microbial life deep within the Earth’s crust
vast amounts of nuclear waste we had buried in sealed containers, which could easily be dissolved by acid-producing microbes
• The US Department of Energy returned rocks containing live bacteria from a 0.5km depth, and from oil wells at a depth of 4km
• These bacteria were thermophilic – the temperature raises by 20oC with every kilometer of depth, until you reach the core, where the temp is 3000oC

Question 5

Ascent from hades 2

Answer 5

It was at first assumed that the mesophile-thermophile- hyperthermophile gradient found with increasing depth represented specialised organisms which had found their way deep into the crust and evolved to cope with the harsh conditions
• However, on closer inspection it became apparent that the opposite was true – life had originated from hyperthermophilic organisms deep in the crust and then some organisms had migrated toward the surface and evolved to cope with the colder conditions

Question 6

Ascent from hades clues

Answer 6

1) The impacts from cosmic bombardment would have been greatly reduced deep within the Earth’s crust, particularly the crust beneath the sea, providing relatively stable conditions for long periods of time
2) The surface would also have contained other threats – the level of ultra-violet radiation would have proved deadly with no ozone layer, and the atmosphere was highly poisonous
3) Volcanic processes within the crust produce all the right chemicals involved in life, and which were absent from the early atmosphere
4) The most convincing argument in support is that gene sequencing (which determines how long ago organisms separated genetically, and how basic their genetic structure is) indicates that the earliest organisms were hyperthermophiles