Sand dunes, Robinson explains by way of example, can bury a fresh lava flow and protect it from being cratered for tens of million of years. If unearthed, it will have the appearance of having flowed recently. Another pitfall, according to Robinson, concerns the martian cratering rate, a number he describes as very poorly known. "So caution's the word," he concludes.
Mars geologists generally agree the planet saw volcanic activity within the last 100 million years. And such activity, if it still continues in the geological present, might account for some or all of the methane observed by Mars Express. Because methane doesn't linger in the martian environment, it needs replenishment. That could be the fingerprint of recent activity.
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