Earth Day Origins Traced to the Moon
April 15, 2010
As the 40th anniversary of Earth Day approaches, a global audience turns its attention to Earth and ways of making the planet a healthier and more sustainable place. The “green” movement has many influences, one of which was surprisingly the Apollo program, which raised public awareness of the environment by offering a new perspective of Earth as well as providing insights into Earth’s origins. Exploration of the Moon created the iconic view of Earth that now adorns the Earth Day flag and book covers of numerous environmental and ecological texts.
Dr. David Kring, a geologist and Senior Staff Scientist at the Lunar and Planetary Institute (LPI) in Houston, says “Lunar exploration has altered our view of Earth, its ecosystems, and the evolution of a habitable world.”
Because Earth Day’s origins can be traced to the Apollo missions, it is only fitting to recognize the significant contributions lunar exploration has made to better understand planet Earth over the last four decades.
- It is no accident that the first Earth Day (1970) occurred a few months after the first Apollo landing (1969). Views of whole Earth hanging in space as a singular home for all humanity were first generated by the Apollo 8 crew when they made their pioneering orbit of the Moon and by subsequent lunar missions, including a favorite “Earthrise” view of Apollo 11 and the final view from Apollo 17 that NASA often uses to describe Earth as an “isolated ecosystem floating in space.” Having witnessed the beauty of those views, NASA has continued to capture images from space and created the stunning “Blue Marble” views of our planet.
- Exploration of the Moon taught us that Earth probably formed in a catastrophic impact with another planet half its size about 4.5 billion years ago. That collision threw a cloud of debris into orbit around Earth that eventually accreted to form the Moon. From that moment, the environment of Earth began to evolve into the life-sustaining planet we now enjoy.
- Exploration of the Moon and, in particular, analyses of lunar rocks taught us that the Earth-Moon system continued to be bombarded by asteroids and comets. There may have been a particularly intense period of bombardment ~3.9 to 4.0 billion years ago that is nearly coincident with the earliest evidence of life on Earth. That coincidence has caused geologists to wonder if this bombardment may be implicated in the origin and early evolution of life on Earth.
- The impact bombardment that preceded that earliest evidence of life resurfaced Earth, so it looked like the heavily cratered surfaces of the Moon, Mars, and Mercury. It destroyed a lot of the rocks on the surface, so we are left with only a few mineral zircon relicts that are older than 3.9 billion years.
- Analyses of these impact events also teach us that the bombardment, while dramatic, did not deliver Earth’s water. Rather, Earth’s water was delivered in an earlier epoch prior to 4 billion years ago. The seas of Earth appear to be a very early evolutionary feature.
- Lunar exploration further caused geologists to wonder if impact events may have affected the later evolution of life on Earth. That revolutionary idea led to the impact-mass extinction hypothesis and the realization that an asteroid impact terminated the age of dinosaurs and ushered in the age of mammals.
- Many calamities in Earth history were caused by an impact’s ability to severely alter global environments and cause ecosystems to collapse. The Chicxulub impact crater, for example, caused deforestation, acid rain, and greenhouse warming, which are similar to the problems that plague us today. Earth’s environment is a uniquely hospitable, but potentially fragile, place.
- The Moon illustrates that planetary bodies too small in size and without sufficient gravity cannot hold onto an atmosphere. Earth is a clement place in part because of its large size.
- When life formed on Earth, the Moon was much closer and appeared about 2.5 times larger in the sky. This proximity to Earth caused larger tides that may have been important to kick-start metabolic processes, and thus life, in intertidal zones. Lunar laser reflectors placed on the Moon’s surface during the Apollo missions indicate the Moon is traveling 1.5 inches per year (3.8 centimeters per year) away from Earth.
- Without the Moon, Earth’s axis would be much less stable, causing much greater fluctuations in climate, perhaps too great for life to survive.
Because Earth lost its own geological record due to the continuous recycling of the surface, we must rely on the Moon to discover the earliest evolutionary and environmental details of our home planet. Kring says “we should celebrate this Earth Day by looking at the reflection of Earth history in the Moon.” He adds that “future lunar exploration will undoubtedly continue to enhance our understanding of the origin and evolution of life on Earth.” On this 40th anniversary celebrating our home planet, humankind must continue to look skyward to the Moon and beyond for answers to many of Earth’s unsolved mysteries.
For more information, visit
Center for Lunar Science and Exploration
Terrestrial Impact Craters and Their Environmental Effects
The Lunar Cataclysm Hypothesis
Last updated April 14, 2010
