Astronomy 1021 Chapter Notes - Chapter 19: Cambrian Explosion, Kic 8462852, Outer Space
28 May 2018
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⇀Astronomy 1021↼
Chapter 19:
➣Are we Alone?
•MW has 100 billion stars
•Observable Universe has 100 billion galaxies
•Probability Earth is the only planet with life is very low
➣What is Life?
•Difficult to concisely define
•Life is a process
•Certain characteristics shared across all living things
➣Life on Earth is Carbon-Based:
•Carbon (C) is a “social” element
•C is very abundant in the Universe
•On Earth, life is C-based
➣Fossils:
•Relics of organisms that lived and died a long time ago
•Formation process:
➣Fossil Dating:
•Relative dating through layers
•Absolute dating through radiometric ages
➣Older Fossils:
•Fossils in older rocks become increasingly difficult to recover
•Older rocks are rarer
•Older rocks transform
•Older life was microscopic
➣Oldest Fossils:
•4.6 billion years: Earth forms
•4.3 billion years: oceans
•3.9 billion years: late heavy bombardment (LHB)
•3.5 billion years: life thriving
➣Early Life:
•May have resembled the bacteria today found near deep ocean volcanic vents (black smokers) and
geothermal hot springs
➣Conclusions:
•Life existed as soon as it could
•Suggests life forms easily
➣Theory of Evolution:
•Fossils showed evolution had occurred, Darwin explained how (1859)
•Fact 1: Overpopulation and competition for survival
•Fact 2: Individual variation
•Inescapable conclusion: Unequal reproductive success (or “natural selection”)
➣Life = Chemistry:
•Deoxyribonucleic acid (DNA) is the molecule that holds life’s information
•Evolution occurs because of mutations (random differences in DNA patterns)
•Mutations are random: could be good or bad
➣Beneficial Mutation Example:
•A squirrel with a heavier coat of fur will, on average, survive longer and produce more offspring than
its normal contemporaries – similarly for offspring
➣Life on Earth is Diverse:
•Animals are only a small subset of life as we know it
•Lots of evidence for evolution; leads to “tree of life”
➣Extremophile Example: Thermophiles:
•“Heat-loving”
•Microbes in hot water
•Not photosynthetic
•Energy is from simple chemical reactions
•Protected from UV radiation and impact effects
➣Ingredients for Life:
•Chemicals
•Water
•Energy
•Chemicals and energy are abundant throughout the universe; water seems to be the key
➣Miller-Urey Experiment (1952):
•Recreate early Earth conditions
•Complex organics formed “easily” and spontaneously
•Have not been able to recreate life yet
➣(Ingredients for) Life Brought to Earth:
•Many complex molecules found in space
•Extremophiles can survive a variety of harsh environments
➣Brief History of Earth:
➣Potential Life in the Solar System:
Water is key:
•Mars
•Jupiter’s moons
•Saturn’s moons
➣Life on Exoplanets: Previous Considerations:
Years Ago
Event
4.5 billion
Earth formed
4.3 billion
Oceans formed
3.9 billion
Life takes hold (after late heavy bombardment?)
2.7 billion
Cyanobacteria alive (see pictures below)
542 million
Cambrian explosion
250-65 million
Dinosaurs dominate; small mammals present
Few million
Earliest humans
Document Summary
Are we alone: mw has 100 billion stars, observable universe has 100 billion galaxies, probability earth is the only planet with life is very low. What is life: difficult to concisely define, life is a process, certain characteristics shared across all living things. Life on earth is carbon-based: carbon (c) is a social element, c is very abundant in the universe, on earth, life is c-based. Fossils: relics of organisms that lived and died a long time ago, formation process: Fossil dating: relative dating through layers, absolute dating through radiometric ages. Older fossils: fossils in older rocks become increasingly difficult to recover, older rocks are rarer, older rocks transform, older life was microscopic. Oldest fossils: 4. 6 billion years: earth forms, 4. 3 billion years: oceans, 3. 9 billion years: late heavy bombardment (lhb, 3. 5 billion years: life thriving. Early life: may have resembled the bacteria today found near deep ocean volcanic vents (black smokers) and geothermal hot springs.
