That gives scientists some clues about what the ancient Martian atmosphere may have been like.

FORBES: Meteorite Shows Evidence Of Water On Ancient Mars

This El Dorado-inspired looting of gold has meant that the vast majority of precious pre-Columbian gold objects have been melted down and the real value of these artefacts as clues to the workings of an ancient culture have been lost forever.

BBC: El Dorado: The truth behind the myth

Clues to its location are provided in ancient Indian texts.

BBC: NEWS | South Asia | Search for India's ancient city

The sizes and shapes will give them clues to the speed and distance of the ancient water flow.

BBC: Curiosity Mars rover beams images of ancient streambed

As researchers pick up garbage left by ancient humans, researchers say they're also finding clues about the past climate.

NPR: History Emerging from the Ice

That could give scientists clues as to how, where and when the water flowed on the ancient surface of Mars.

FORBES: Curiosity Finds Evidence Of Ancient Stream On Mars