Geoscience Reference
In-Depth Information
servicing the burgeoning demands for what are seldom routine sample dating
analyses.
THE EARLY EARTH
Much of Earth's present-day structure and significant parts of its history can
be traced back to events that occurred within the first few hundreds of million years
after its formation. Understanding the processes involved in Earth accretion and early
chemical differentiation is essential for establishing the initial thermal conditions of
the dynamical systems of the interior, the volatile content of the planet, and the
origins of the continents that have led to the current Earth system. Recent progress on
understanding the early Earth has been substantial, yet we have only begun the task of
resolving the timing, nature, and interrelationships of the most decisive events,
including cataclysmic impacts; magma oceans; segregation of the core; early forms of
continents, oceans, and the atmosphere; the onset of plate tectonics; and, of course,
the origin of life. Because Earth grew and differentiated rapidly, the energy available
to the Earth system during its early history was far higher than today, permitting
whole sets of physical and chemical processes without counterparts in the modern
Earth. The overarching challenge here is to understand how Earth transitioned from
its formative state into the hospitable planet of today (see Box 2.1). Lessons learned
from the early Earth will help us interpret the processes occurring in the hundreds of
extrasolar planetary systems now being discovered by astronomers.
BOX 2.1
Planetary Science
Earth's interior and surface environments are profoundly influenced by our position in
the Solar System and interaction with the Moon and other planets. The moon stabilizes the
orientation of Earth's spin axis and promotes climate stability, in stark contrast to, for
example, Mars. Gravitational interactions between Earth and other planets, particularly
Jupiter, cause small variations in the eccentricity, obliquity, and precession of Earth. While
small, these variations are likely partly responsible for ice ages.
The discovery of hundreds of planets orbiting other stars, so-called extrasolar
planets, provides a new opportunity to understand whether the architecture of our solar
system and presence of an Earth-like planet in the habitable zone are common. Planets
around young stars may also offer a window into the earliest Earth. Limited information,
however, is available about these planets, and in the best cases we know their mass, radius,
eccentricity, and temperature and are able to detect some gases.
Continued exploration of our own solar system has led to new, unexpected
discoveries: an active dynamo on Mercury, eruptions on Enceladus (see Figure B2.1), and
methane lakes on Titan. These discoveries provide new opportunities to test our
understanding of the basic processes that govern planetary evolution and interactions
between Earth systems, particularly the interior, the geodynamo, surface environments, and
the atmosphere.
Understanding these new discoveries and further exploration of our solar system are
activities typically supported by the National Aeronautics and Space Administration (NASA).
Nevertheless, there are opportunities to better understand Earth systems and the earliest
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