Most key in this data is that the olivine is NOT found all over Mars. In fact it is overwhelmingly missing from the surface of Mars. Here is an equivalent way of expressing the data on olivine on Mars:

"98% of Mars surface could have been wet recently."

Why you have to read the fine print:

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From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: Green Mineral Indicates Mars Is Dry
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.geology
Date: 2003-10-24 10:16:25 PST

This area is only 30,000 sq. kilometers or comparable to an area of
300km by 100km.
Saying Mars is dry on the basis of this is like saying Earth is dry
on the basis of the Sahara desert.

An earlier report measuring olivine over large parts of Mars found
olivine on 1 million square miles:

New Evidence Suggests Cold, Dry Mars
posted: 07:18 am ET
02 November 2000
http://www.space.com/scienceastronomy/solarsystem/mars_dry_001101.html

This report also claimed Mars has always been dry on this basis. The
problem is that Mars with a diameter of about 4000 miles means 1
million square miles corresponds to about 2% of the Martian surface,
using the formula for surface area for a sphere 4*Pi*radius^2 and 2000
miles for the radius.
But Earth itself has desert areas that account for 20% of its land
area, and even when you account for the fact that the Earth is covered
by 70% water, that means deserts on Earth account for 6% of its total
surface area:

Desert Habitats
Deserts of the World
"Deserts cover about one fifth (20 percent) of the earth's land area.
The desert is a harsh environment with very little rainfall and
extreme temperatures."
http://www.enchantedlearning.com/biomes/desert/desert.shtml

So saying Mars is dry by looking at the portion that contained
olivine ignoring the overwheling majority that did not is like looking
at only the desert areas on Earth and concluding that it is dry, and
ignoring the wet areas.

Bob Clark

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