Mars, Page 13: [Previous Page] [Next Page] [Syllabus] Textbook pages 142 - 159

The Geological History of ALH84001

ALH84001 is an igneous rock (formed from volcanism), containing inclusions of calcite. We've talked about why we think its from Mars. What can we tell about its geological history?

4500 million yrs ago	The rock was formed (crystallized). Likely at about the same time Mars was formed.
4000 million yrs ago	Rock was shock impacted, but did not leave surface. Probably from planetesimal hitting Mars.
3600 - 1800 million yrs ago	Carbonate minerals were deposited in the rock. Must have been liquid water during this time. Unfortunately, aging carbonates is nearly impossible. But the age range suggests life existed during the mid-epoch of Mars history.
16 million yrs ago	The rock was ejected in to space, probably from another meteoritic impact. It likely had a complex orbit which brought it in towards Earth.
0.013 million yrs ago (13,000 yrs)	Landed in Antarctica.
0.000021 million yrs ago	Found in Antarctica (1984)

The issue of the geological history of the Martian Meteorite is not disputed. It's what was found in the carbonate deposits which is!

Before we discuss the evidence, we must be sure of a few things.


• Could the rock have been contaminated since it came to Earth?
  Probably not.
• What about the 13,000 years in the Antarctic?
  Other meteorites collected in Antarctica show no evidence for contamination.
• What about when it was transported to Johnson Space Flight Center?
  The meteorites are never touched, sealed in sterile, airtight containers.
• What about while it was being tested?
  During analysis, the samples are handled with dust-free gloves and prepared on clean Al surfaces. Disks of quartz handled in the same way show no evidence contamination either.