Lecture 1: The Biodiversity Crisis: Science and Understanding 3 Flashcards
Formation of the earth
Planetesimals aggregate and due to gravity, large collisions are unavoidable, so that protoplanets and eventually full planets form – the Earth formed 4.5 billion years ago
• One such impact gave the early Earth its iron core and formed our moon
Impact of that magnitude
An impact of this magnitude would have baked the Earth dry of any volatile material that may have been present in the initial formation (e.g. organics such as amino acids, water – ingredients essential to life)
Interstellar distance
Further away from the sun, things happened more slowly because there was less material in the system and less heat – hydrocarbons (H+C) would have been preserved from the sun’s heat, and substances like water and sulphur could solidify
- Silicate and hydrocarbon particles (‘dust’) towards the edges of solar system would collect ice crystals which began to aggregate and Jupiter, Saturn, Uranus and Neptune were formed, sucking in much of the distant material
- Crucially, beyond the orbit of Neptune the ice and rock aggradations were too small and scattered to form planets, and so many comets and asteroids form belts in these locations – mainly the Kuiper belt and the Oort cloud
Our solar system
Our solar system (the sun and all the planets) in turn orbits the supermassive black hold that lies at the centre of the Milky Way
• The solar system completes its orbit once every 250 million years – but during its orbit it comes into close proximity to other systems, which can displace the Oort cloud and send comets and asteroids back towards the Sun and its planets
Early earth
The early Earth was devoid of volatile material and organics required for life, and had no atmosphere – all hydrogen, helium etc. within the inner solar system had been blown away by solar winds
Comets and Meteorites
Comets and meteorites bombarded the Earth frequently, delivering many key substances –
silicates to form the rocky crust, enough water to fill the Earth’s oceans, and gradually a dense (and highly toxic) atmosphere formed, helped along by volcanic eruptions
• These conditions could not originally support life – atmospheric pressure was huge, the moon was closer, oceans deep and tides massive – days lasted only a few hours as the Earth spun so fast
Bombardment
Bombardment was heavy after the Earth formed (around 4.5 billion years ago) for around 300 million years, and then declined, only to increase massively between 4-3.8 billion years ago before declining again
Each asteroid or comet which hit the Earth would have potentially deposited and/or destroyed organics and affected the atmosphere
what is apparent is that the Earth could have gained enough carbon to make the biosphere from comet impacts, as well as all of its water – other planets have not developed in the same way following strikes, for varying reasons
Life on earth
Significantly, life began on Earth between 3.8-3.5 billion years ago, shortly after the heavy bombardment (which would have sterilised Earth of life had it existed) ceased, leading to two broad hypotheses:
1) cometary bombardment provided the correct materials so that abiogenesis could occur as soon as frequent disturbance ended,
or 2) life arrived from space
What is life? conditions- reproduction
Reproduction – the driving force, and meaning of, all life
• It is not enough for replication to occur – many non-living things can replicate (crystals, fires); the replicate must be informed replication (from DNA/RNA), and must have a copy of the replication equipment too (i.e. ability to reproduce)
• Note that there are some grey areas, e.g. sterile organisms (such as mules), and those which cannot reproduce without the help of a host (e.g. viruses)
What is life? conditions- metabolism
Metabolism – the creation of usable energy via a sequence of chemical reactions
• Required to complete essential tasks such as movement and reproduction
What is life? conditions-organisation
Organisation – all organisms and their components are incredibly well organised
• This is not just general organisation like that seen in sand dunes or rock formations, due to simple interactions of physical forces – it is informed organisation, i.e. DNA is dictating how the organism will be arranged and function
What is life? conditions-development
Development – all organisms grow and change
• Individuals grow, ecosystems spread and change with succession, and species evolve
• Darwinian evolution and other changes are discussed later
• We still don’t know (and may never know) exactly how abiogenesis occurred, or whether it may have happened elsewhere in the universe, but we are beginning to understand where it may have developed on Earth
