Does Life Begin and Develop?
Sources of 0rganics on Earth
Origin of Life's Cellular Components
Models for Life
Genomic Clues to Evolution
Linking Planetary and Biological Evolution
Life Exist Elsewhere in the Universe?
The Extremes of Life
Past and Present Life on Mars
Life's Precursors and Habitats in the Outer Solar System
Natural Migration of Life
Origin of Habitable Planets
Effects of Climate and Geology on Habitability
What is Life's Future on Earth
Ecosystem Response to Rapid Environmental Change
Earth's Future Habitability
Bringing Life with Us beyond Earth
Question: How Does Life Begin and Develop?
Sources of Organics on Earth
Determine whether the atmosphere of the early Earth, hydrothermal systems
or exogenous matter were significant sources of organic matter.
Determining the primary sources
and nature of organic matter from which living systems emerged on the
prebiotic Earth is still a controversial endeavor. The key proposed sources
include synthesis in the atmosphere of the early Earth; synthesis in warm
hydrothermal systems or in geothermal subsurface environments; delivery
to the early Earth by comets, meteorites and microscopic, interplanetary
dust particles; or some combination of these possibilities. Each hypothesis
leads to different predictions about the composition and availability
of organic starting material and the nature of the earliest pre-metabolic
processes leading to the origin of life. We must, therefore, determine
the relative contributions of each of these sources of organic material
to life's origins on the primitive Earth, and define and characterize
those mechanisms that allowed adequate concentrations of these chemicals
for the necessary interactions and reactions to occur.
Near to mid-term:
- Using space missions and infrared
telescopes, explore how organics, initially synthesized in the interstellar
dust cloud from which the Solar System was formed, are chemically altered
before they are delivered to earth. This research will help to determine
the chemical structure and composition of exogenous organic compounds
and the extent to which they contributed to the inventory of prebiotic
organics on earth. This task will benefit from missions to analyze organic
material in both interplanetary dust particles as well as meteor showers.
In addition, ground, air (SOFIA) and space-based (SIRTF) observatories
will provide key data.
- Conduct realistic laboratory
simulations of chemical reactions under the conditions existing on planetary
bodies, on the surface of the primitive earth and in hydrothermal vents.
Investigate the potential of the synthesized compounds to contribute
to the formation of biological structures.
- Perform computer modeling of
prebiotic chemical synthesis in different environments taking into account
appropriate external constraints, such as energetics, temperature, pressure,
and surface catalysis potential.
- Examine the geological record
for evidence of environmental conditions on the early earth. Examine
ancient rock formations for the signature of early life in the form
of microfossils, isotope ratios and mineral assemblages, and obtain
evidence for the redox state of the earth mantle near the time of the
origin of life. A reducing mantle was essential to maintain a reducing
atmosphere on the prebiotic earth.
- Study natural environments
(e.g., hydrothermal vents) as models for primordial chemistry.
- Perform space missions to characterize
more precisely quantities and compositions of exogenous and sub-surface
- Construct integrated models
of the chemistry on the prebiotic earth that include contributions from
different sources of organic matter and environmental constraints.
- Perform planetary subsurface
missions to obtain virgin endogenous material.
- Perform planetary missions
to understand possibilities for prebiotic evolution.