|
This article is credited to NASA.
Top Ten Scientific Discoveries Made During Apollo
Exploration of the Moon
The Moon is not a primordial object; it is an evolved terrestrial planet
with internal zoning similar to that of Earth.
Before Apollo, the state of the Moon was a subject of almost unlimited
speculation. We now know that the Moon is made of rocky material that
has been variously melted, erupted through volcanoes, and crushed by
meteorite impacts. The Moon possesses a thick crust (60 km), a fairly
uniform lithosphere (60-1000 km), and a partly liquid asthenosphere
(1000-1740 km); a small iron core at the bottom of the asthenosphere
is possible but unconfirmed. Some rocks give hints for ancient magnetic
fields although no planetary field exists today.
The Moon is ancient and still preserves an early history (the first
billion years) that must be common to all terrestrial planets.
The extensive record of meteorite craters on the Moon, when calibrated
using absolute ages of rock samples, provides a key for unravelling
time scales for the geologic evolution of Mercury, Venus, and Mars based
on their individual crater records. Photogeologic interpretation of
other planets is based largely on lessons learned from the Moon. Before
Apollo, however, the origin of lunar impact craters was not fully understood
and the origin of similar craters on Earth was highly debated.
The youngest Moon rocks are virtually as old as the oldest Earth
rocks. The earliest processes and events that probably affected both
planetary bodies can now only be found on the Moon.
Moon rock ages range from about 3.2 billion years in the maria (dark,
low basins) to nearly 4.6 billion years in the terrae (light, rugged
highlands). Active geologic forces, including plate tectonics and erosion,
continuously repave the oldest surfaces on Earth whereas old surfaces
persist with little disturbance on the Moon.
The Moon and Earth are genetically related and formed from different
proportions of a common reservoir of materials.
The distinctively similar oxygen isotopic compositions of Moon rocks
and Earth rocks clearly show common ancestry. Relative to Earth, however,
the Moon was highly depleted in iron and in volatile elements that are
needed to form atmospheric gases and water.
The Moon is lifeless; it contains no living organisms, fossils, or native
organic compounds.
Extensive testing revealed no evidence for life, past or present, among
the lunar samples. Even non-biological organic compounds are amazingly
absent; traces can be attributed to contamination by meteorites.
All Moon rocks originated through high-temperature processes with
little or no involvement with water. They are roughly divisible into
three types: basalts, anorthosites, and breccias.
Source: NASA
Basalt with dark gray igneous rock.
Basalts are dark lava rocks that fill mare basins; they generally resemble,
but are much older than, lavas that comprise the oceanic crust of Earth.
Anorthosites are light rocks that form the ancient highlands; they generally
resemble, but are much older than, the most ancient rocks on Earth.
Breccias are composite rocks formed from all other rock types through
crushing, mixing, and sintering during meteorite impacts. The Moon has
no sandstones, shales, or limestones such as testify to the importance
of water-borne processes on Earth.
Early in its history, the Moon was melted to great depths to form
a "magma ocean." The lunar highlands contain the remnants
of early, low density rocks that floated to the surface of the magma
ocean.
Source: NASA
Anorthosite is a white rock with a black glass coating.
The lunar highlands were formed about 4.4-4.6 billion years ago by flotation
of an early, feldspar-rich crust on a magma ocean that covered the Moon
to a depth of many tens of kilometers or more. Innumerable meteorite
impacts through geologic time reduced much of the ancient crust to arcuate
mountain ranges between basins.
The lunar magma ocean was followed by a series of huge asteroid impacts
that created basins which were later filled by lava flows.
The large, dark basins such as Mare Imbrium are gigantic impact craters,
formed early in lunar history, that were later filled by lava flows
about 3.2-3.9 billion years ago. Lunar volcanism occurred mostly as
lava floods that spread horizontally; volcanic fire fountains produced
deposits of orange and emerald-green glass beads.
The Moon is slightly asymmetrical in bulk form, possibly as a consequence
of its evolution under Earth's gravitational influence. Its crust is
thicker on the far side, while most volcanic basins -- and unusual mass
concentrations -- occur on the near side.
Mass is not distributed uniformly inside the Moon. Large mass concentrations
("Mascons") lie beneath the surface of many large lunar basins
and probably represent thick accumulations of dense lava. Relative to
its geometric center, the Moon's center of mass is displaced toward
Earth by several kilometers.
The surface of the Moon is covered by a rubble pile of rock fragments
and dust, called the lunar regolith, that contains a unique radiation
history of the Sun which is of importance to understanding climate changes
on Earth.
The regolith was produced by innumerable meteorite impacts through geologic
time. Surface rocks and mineral grains are distinctively enriched in
chemical elements and isotopes implanted by solar radiation. As such,
the Moon has recorded four billion years of the Sun's history to a degree
of completeness that we are unlikely to find elsewhere.
--------------------------------------------------------------------------------
Responsible NASA Official: Dr. Carlton Allen
|
