Meteorites and Life on Mars
- Mars is a particularly interesting place to study because...
- Its surface is preserved in a state that may be
characteristic of Earth a few hundred million years after
- Little if any of the Earth's crust from this time period
is preserved today.
- If Earth and Mars initially evolved in parallel, information about conditions leading to the emergence of life
may be preserved on Mars.
- Detailed exploration of the Martian surface and ultimately returning samples is critical to understanding the history of Mars.
- The earliest Martian sample return will occur around 2015.
- Fortunately the Solar System delivers such samples to us
- A meteorite found in Antarctica in 1984 clearly originated from the surface of Mars.
- The age of the meteorite, about 4 billion years, was less than the typical 4.55 billion years characteristic of typical meteorites.
- This younger age already suggest an origin on a planetary surface which was resurfaced after the Solar System formed.
- The chemical composition of the meteorite differs
from most other meteorites and is similar to that of
meteorites known to be of Martian origin.
- These meteorites contain trapped gasses that clearly came
from the Martian atmosphere.
- Large impacts on planetary surfaces can eject surface rocks into interplanetary orbits.
- Dozens of meteorites have been identified as coming from
Mars or the Moon.
- The rock in question solidified on the Martian surface
4 billion years ago.
- This age is determined from radioactive dating
- 13 million years ago a large impact
sent it into solar orbit.
- This date is determined from the "cosmic ray exposure"
age of the rock.
- In space the rock will be bombarded with cosmic
ray particles and the exposure accumulates with time.
- About 10,000 years ago it fell onto the Antarctic ice sheet.
- This age is estimated from the meteorite's location
on the ice sheet and the depth of weathering on its surface.
- Physical and chemical analysis of this meteorite shows that:
- It was fractured billions of years ago, probably by meteorite
impacts on the Martian surface.
- Liquid water percolated through the fractures producing
- These carbonate globules
contain magnesium and iron-rich
minerals which are similar to the waste products of
- These minerals could also be produced by natural causes.
- The globules also contain complex carbon-based molecules
which are similar to the decay products of Earthly bacteria.
- These complex carbon-molecules can also be produced
by natural causes.
- The rims of the globules contain microscopic structures
which look very much like Earthly nano-bacteria -- although they
are at least 10 times smaller.
- The results are suggestive of early life on Mars, but thoroughly
inconclusive and terribly controversial. The scientific community does not regard this work as evidence for early life on Mars.
- The most important lesson, however, may be that Mars could have been
the source of life on Earth, or vice versa.
- Estimates are that a billion tons of Martian material are now
on the Earth.
- Life could survive inside a rock fragment during the
few years it would take for a direct trip from Mars to Earth.
- If one planet forms life, all the others could/will be inoculated.
- We may very well be Martians.
Main Martian Points
- Mars had a warmer and wetter beginning thanks to a thicker atmosphere and a stronger greenhouse effect.
The first few hundred million years of Martian history may have been ``Earthlike" with bodies of liquid water on the Martian surface.
- Mars' geological activity largely ceased after that initial few hundred million years. The record of the state of the Martian surface at that time remains today (something inaccessible on Earth).
- Impacts can launch rocks off of a planet's surface into interplanetary orbits. Those rocks can contain micro-organisms which can survive the
trip from one planet to the other.
Earth may have innoculated Mars.
- Or... Life in the solar system may have originated on Mars,
and Mars may have innoculated Earth.
- The ``Rare
Earth" implications of this scenario could be significant.
Imagine if life could not originate on Earth because of the
initial state of the Earths surface, while Mars was ripe for the
emergence of life. Mars then became inhospitable at the time
that the Earth was just becoming suitable for life... Maybe life
has to be cooked up on a small world before being transferred to
one more appropriate for sustaining it for billions of years???
Revised April 18, 2005