AST 2037 Lecture Notes - Lecture 10: Tunguska Event, Surface 2, Billion Years
27 May 2018
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Lecture 9 - Ch.5 Nature of Life
1. 6 characteristics of life
a. Uses energy
b. Ordered structure to the components of molecules and atoms
c. Reproduction
d. Growth and development
e. Response to environment
f. Evolutionary adaptation
i. Occurs on short and long timescales
ii. Living organisms change over successive generations as they respond and
adapt to environment (well before discovery of DNA)
iii. Lamarck believed long necks of giraffes evolved to reach high tree leaves
over long time
iv. Evidence of evolution: antibiotics weakening on treatments of diseases
Lecture 10 - Ch.5 cont.
Cells
1. Roles = concentrate molecules and protection from environment
2. Two types
a. Eukaryote = has nucleus, size: 10 microns
b. Prokaryote = no nucleus, size: 0.5 microns
3. Elements of life: O2, C, H (in order of abundance)
a. Carbon forms basis of cells and is much more abundant in life than in the
environment
b. Carbon is diverse in its ability to form chemical bonds and allows for complex
chemistry of life
i. Only silicon has similar ability for chemical bonding
ii. Important to look at structure of electrons (esp. outer shells), and carbon
has a half-filled outer shell (4 e-), which is optimum number of very strong
bonds possible
iii. Ionic (generally weak) and covalent (strong) bonds
iv. C compounds can be dissolved in liquid and form hydrocarbons that form
building blocks of life
c. Silicon less likely to form life due to:
i. Si bonds are fragile
ii. Bond strengths are not advantageous for complex chemistry
iii. Tends to form strongest bond with oxygen --> limits amount of Si for
organic chemistry
d. Liquid water
i. Common media of transport
ii. Pola oleule: dissoles othe polas
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