Life and the Cosmic Environment
The Earth does not operate as a closed system. Basic
planetary and stellar processes may be involved in encouraging or hindering
biological evolution. Starting at the geological level, we note that convection
within a planet can not only cause plate tectonics, but also change sea levels,
ocean currents, wind patterns, and seasonal extremes. This process has been
responsible for isolating landmasses such as
Cosmic intruders have been decisive in the history of life.
The first wave of impacts early in the Earth's history was beneficial to life,
bringing in substantial amounts of life's essential gases and organic
materials. Since then, the much rarer large impacts have been catastrophic. The
impact of an asteroid or comet could have damaged the ozone (O3) layer,
exposing organisms to enhanced radiation. The
Subtle changes in the Earth-Sun system can also influence life. During the Earth's history, the Sun has brightened by 30%, and even smaller changes in the Sun's radiation since then may have caused climate change. Astronomers believe that slight changes in the Earth's orbit and the tilt of the planetary axis to the plane of the ecliptic due to gravitational forces caused major climate changes such as the ice ages. Recent marine studies of traces from the past 700,000 years have shown decisively that cycles of climatic change, including several pulses of continental glaciation, can be tied to the so-called Milankovich cycles of orbital change in the Earth-Sun-Moon system.
During life's tenure, the solar system has probably been influenced by the gravity of nearby passing field stars and by blasts of radiation and high-energy particles from nearby supernovae. On a larger scale, life's history has encompassed 18 galactic years, and the Earth has passed through denser material in the plane of the Milky Way galaxy perhaps 200 times. We are only just beginning to discover the signatures of these cosmic events in our rock and fossil records and the effects they have had on the evolution of advanced life.
EARLY ESTIMATES OF EARTH’S AGE
PROBABILITY AND IMPACTS
ENVIRONMENTAL CHANGE ON EARTH
EFFECTS OF THE SUN ON THE EARTH
FROM MOLECULES TO CELLS
THE ORIGIN OF LIFE ON EARTH
SOLAR CHROMOSPHERE AND