The Saylor Foundation’s “Answer Key to Problem Set 1”
1. What are the fundamental characteristics of “life?”
Living organisms are characterized by several distinguishing characteristics.
These features include:
a. Organization
b. Homeostasis
c. Adaptation
d. Reproduction and heredity
e. Growth and development
f. Energy acquisition and release
g. Detection and response to stimuli
2. Under what conditions do we think life as we know it began?
Evidence suggests that life has existed for approximately 3.7 billion years on
Earth. The oldest fossils date to 3.4 billion years ago. Current hypotheses
concerning how life arose suggest that chemical reactions occurred, synthesizing
amino acids and other inorganic precursors, and that actual life began using
these building blocks in thermal vents in the ocean.
3. What things are necessary for life?
Water is a molecule required for life. The four elements that make up the
majority of living matter and therefore should be of interest when searching for
the possibility of life on other planets are oxygen, carbon, hydrogen, and
nitrogen.
4. Beyond conditions that may be appropriate for life, what evidence should we look
for to indicate past or present existence of life?
To indicate life is currently present, scientists could look for waste products (e.g.
CO2).
NASA developed 8 criteria to determine if life was present in a geological sample
(e.g. a meteorite found on earth). Some of these criteria (listed below) could help
scientist determine if life is present on other planets:
a. “Does the sample contain evidence of cellular morphology and colonies?”
b. “Is there any evidence of biominerals showing chemical or mineral
disequilibria?”
c. “Is there any evidence of stable isotope patterns unique to biology?”
d. “Are there any organic biomarkers present? Are the features indigenous to the
sample?” (Gibson et al., n.d.).
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5. The search for life sometimes begins with a search for water. Why?
Water is known as a universal solvent. Many substances can dissolve in water,
allowing them to pass freely through the water, eventually coming in contact with
chemical bonds, breaking them and allowing other bonds to be formed. Water,
therefore, facilitates necessary chemical reactions for all organisms. Due to
water’s dissolving properties and its necessity for known chemical reactions,
such as photosynthesis and metabolic process, it is a key compound and a target
molecule when searching for the presence of life or the ability for life to exist on
other planets.
6. What is it about water that makes it uniquely important for life as we know it?
The properties of water that make it essential for life are:
a. Water molecules are cohesive (water molecules cling to each other due to
hydrogen bonding) and adhesive (water can cling to other polar substances).
b. Water is a solvent.
c. Water has a high surface tension.
d. Water has a high heat capacity (a lot of energy is needed to change the
temperature of water).
e. Water is less dense as ice compared to when in its liquid form (allowing it to
float leading to the survival of organisms in oceans, ponds, and streams).
7. If life began under different conditions, how might the things that we search for
differ?
If life arose in different conditions than those on earth, scientists may still use
some of the same conditions when searching for life (e.g. does the sample
contain evidence of cellular morphology and colonies? Are the features
indigenous to the sample?” (Gibson et al., n.d.). However, they may have to
search for other types of biomolecules/waste products.
Reference
Gibson, E. K., Westall, F., McKay, D. S., Thomas-Keprta, K., Wentworth, S., &
Romanek, C. S. (n.d.) Evidence for ancient Martian life. Retrieved September
15, 2011, from http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6142.pdf
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