Astronomy 1021 Chapter Notes - Chapter 19: Cambrian Explosion, Cyanobacteria, Thermophile
28 May 2018
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Astronomy 1021
Chapter 19: Life in the Universe
Life on Earth
•Astrobiology- scientific search for life in the universe; focuses on understanding the origin and
evolution of life on earth, searching for other habitable worlds, searching for evidence of actual
life on other worlds
•MW has 100 billion stars; observable universe has 100 billion galaxies; probability earth is the
only planet with life very low
When Did Life Arise on Earth
•Evidence supports that life began early in Earth’s history (evidence being fossils)
•Life is a process of certain characteristics shared across all living things
•Life on Earth is carbon-based: Carbon is a ‘social’ element, very abundant in our Universe, on
earth, life is C based
•Fossils- relics of organisms that lived and died a long time ago; formation process- the organisms
fall to the bottom of a water body and get buried in layers of sediments, overtime the sediments
compress into rocks
•Can reconstruct history of life through Fossil Dating: relative dating through layers- anything
closer to the surface is younger, anything near the bottom of the sedimentary rock is older
oAbsolute dating through radiometric ages- through isotopes
•Older Fossils- fossils in older rocks become increasingly difficult to recover (b/c they are very
tiny); older rocks are rarer, older rocks transform (and don’t preserve intact fossils), older life was
microscopic
oOldest fossils: earth forms 4.6 billion years ago; Oceans formed 4.3 billion years ago, late
heavy bombardment occurred 3.9 billion years ago, life was thriving 3.5 billion years ago
oEvidence comes from stromatolites- rocks that have similar size, shape, interior structure
to sections of modern mat-shaped formations called living stromatolites
•Early life may have resembled bacteria today found near deep ocean volcanic vents (black
smokers) and geothermal hot springs
•Proto-life before LHB?- Extremophiles exist before LHB and still existing; so life existed as soon
as it possibly could, and the evidence suggest that life forms easily
How Did Life Arise on Earth- Theory of Evolution
•Fossils showed evolution had occurred, Darwin explained how (1859)
oFact 1- overpopulation and competition for survival- for resources like food; some
species were able to survive
oFact 2- Individual Variation- even within species there is variation; some species have
skills that allow them to survive certain conditions better (like harsh winters)
oConclusion- unequal reproductive success (natural selection)
•Life= chemistry: DNA is the molecule that hold life’s formation; evolution occurs b/c mutations
(Random differences in DNA patterns); mutations are random- could be good or bad
