Life in the Universe Flashcards
What is life?
Existence in the physical world
- the quality that makes living animals and plants different from dead organisms and inorganic matter
a process that includes the ability of an organism to take in energy from the surroundings, adapt to the environment, grow, and reproduce
life on earth
The Earth is the only place known to harbour life
The Earth was formed 4.54 billion years ago and the oceans formed 4.41 billion years ago
Life has existed on Earth for approximately one third of the age of the Universe
- The earliest undisputed evidence of life on Earth dates from 3.5 billion years ago but there is evidence for much earlier forms of life
- Microorganisms found in deep ocean hydrothermal vents
- Estimated age range: 3.8 to 4.3 billion years old
The self-replicating molecule
A molecule appeared with the remarkable property of
replicating itself
These self-replicating molecules were a rudimentary form
of modern DNA/RNA – the seeds of all life on Earth
Interactions between molecules were basic, driven only by
basic physics and chemistry at this point
Darwinian Evolution
two inevitable
natural processes
- Random mutations that occur during the replication
- A selective survival of the offspring that are best adapted to their environment
This process, which Darwin called evolution by natural selection, results in gradual changes in species at the level of the gene over time
Single cell organisms
The process of evolution by natural selection quickly
produced the single-celled organism
Highly “successful” form of life - dominated the Earth for most of its history
They thrived in the harsh oxygen-lacking, conditions of the early Earth and consumed the carbon dioxide and sulphates abundant in the early atmosphere
The Cambrian Explosion
An evolutionary explosion that occurred 540 million years ago in the oceans
Lasted 20 million years
Diversification from basic, single-cell organisms to animals
First time most animal groups appeared in the fossil record
The ancestors of all animal life in existence today
Drivers of the Cambrian Explosion
The drivers of this rapid evolution are still unknown
A sudden rise in oceanic oxygen levels is thought to
be key
Animals require oxygen to produce energy, metabolising food in the presence of oxygen releases great quantities of energy
Drives adaptations such as muscles, nervous systems and the technologies for predation
Likely a complex interplay of various marginal environmental changes and corresponding evolutionary adaptations
Produced the remarkable diversity of life we see today
life timeline
<5 mya: Modern human ancestral lineage and the chimpanzee ancestral lineage split
4 mya: The hominid Australopithecus anamensis
3 mya: Australopithecus afarensis
2.5 mya: Many species of hominid overlapped
~2.5 mya: The Homo clade first appear in Africa
1.5 mya: Hominids departed Africa and into Asia and Europe. These include the ancestors of Neanderthals in Europe and Homo erectus in Asia
100,000 years ago: Human brains reach modern size. Early Homo sapiens lived in Africa. Homo neanderthalensis and Homo erectus lived in other parts of Europe
50,000 years ago: Small groups of modern humans departed Africa
25,000 years ago: Only modern humans, Homo sapiens remain, all other Homo species had gone extinct
Evolution of Human Culture
Humans have the unique capacity to use language to exchange ideas and adapt their behaviour accordingly
The replication of ideas from one brain to another is analogous to the replication of genes from one organism to another - the memes mutate when replicated, and only some of them survive, so are subject to a process of natural selection
This “cultural evolution” is the reason that humans evolved from hunters and gatherers to highly complex modern societies, without significant genetic change
Mass Extinction Events
99% of all life that had existed on Earth is now extinct – 6 billion species
Earth is currently enjoying its 6th mass extinction age - Holocene mass extinction
- Due to human activity, began 12 000 years ago
- Accelerated due to industrialisation, human overconsumption and climate change
- Extinctions occurring at 1000 times the natural rate since 1900
- 25% of wildlife threatened with extinction
Cosmic pluralism
a belief in many worlds like our own with their own inhabitants
Earliest known expressions of secular cosmic pluralism
- India (8th century BC)
- Ancient Greece (6th century BC)
Anaximander was one of the earliest known proponents of cosmic pluralism
Aristotle and later Plato opposed this view – they asserted the Earth was unique
- They won the argument - adopted by the Christian world
Origins of the belief in life beyond Earth
Early recorded cultures believed in Gods who resided in a sort of heaven
Ancient Egypt and Ancient Greece were polytheistic
This is not quite cosmic pluralism
Belief in a reality or “truth” beyond Earth
Pythagoras “discovery” of mathematical deduction led to the belief in an external and exact truth beyond Earth
He discovered a perfection in geometry not found in
reality
Plato’s Theory of Ideas is similar - ideas are
the non-physical essences of all things
- Objects in Earth
are merely imitations of these ideas
Challenging Aristotle – Islamic Thought
Islamic scholars challenged Aristotle’s then widely-held view
They referred to supporting evidence in the Qur’anic verses
- “All praise belongs to God, Lord of the Worlds”
It was thought that there were many worlds similar to the Earth, each with their own life similar to humans
The Copernican Revolution
Copernicus proposed the heliocentric model of the Universe – The Sun at the center of the Solar System
His followers reasoned that cosmic pluralism was a logical extension of heliocentrism
The Copernican Principle
There is nothing special about the Earth, or our place in the universe
The Acceptance of Cosmic Pluralism
During the Enlightenment (late 17th century – 18th century), cosmic pluralism was espoused by many
influential Enlightenment thinkers
An emerging culture of scientific scepticism bounded the question of cosmic pluralism to scientific observations
This “triumph of science” marked the beginning of our
modern understanding of cosmic pluralism
Focus shifted to the observation of cosmic objects and to developing our understanding of life on Earth
The Conditions for life
Carbon (carbon-based lifeform)
Water (water as a solvent)
Energy source (usually a star)
A planetary system with a planet situated in the Habitable Zone
Why Water-Carbon lifeforms?
We already have an example of water-carbon lifeforms here on Earth
The Abundance of the elements
Why is a solvent is needed?
Solvents are considered necessary for the formation and maintenance of life
Solvents allow for the transportation of dissolved substances inside cells
Water is the preferred solvent
Why is water ideal?
It is extremely abundant
It has many unique properties that are useful for processes related to life
Why is carbon ideal?
It is extremely abundant
It has the ability to form complex stable molecules
The Habitable Zone
A circular region around a star where suitable conditions might exist for life
This concept focuses on life’s requirement for liquid water
The habitable zone is generally thought of as the range of distances from the central star in which water could be present in liquid form at a planet’s surface
The Drake Equation
Based on a probabilistic argument
It takes a big, difficult unknown quantity (the number of advanced extraterrestrial galaxies) and breaks it down into smaller, more manageable quantities that can be measured
SETI
Search for Extra-Terrestrial Intelligence
Because planetary systems are so far away, travelling to them is not feasible
The best way contact ETI’s is by communicating via electromagnetic radiation
The Fermi Paradox
The universe is extremely old and it has taken a relatively short amount of time for humans to develop the ability to communicate over interstellar distances
Thus any extra-terrestrial intelligence in our galaxy would have already colonised the galaxy and thus we would have been confronted with their existence
Resolving the Fermi Paradox
There are no intelligent extraterrestrials
Life is common but intelligence is rare
There are invisible communication signals flowing past us that we are not advanced enough to detect
Advanced species do not to interfere with immature, developing intelligences such as our own
The Great Filter - Civilizations that reach a certain level of technology then self-destruct, meaning there are no other civilizations now existing in our Galaxy
