[dribnet]

"There would be few fossil traces of these lost siblings of the Earth."

Our moon is a pretty obvious reminder of Earth's lost sibling Theia.

http://www.astronomy.com/news/2014/06/new-isotopic-evidence-...

[bjelkeman-again]

That could be the kernel of a scifi story. What if Theia had life on it and it spread to earth.

[LarryMade2]

Here's one: the Giants Series by James P. Hogan; starts with Inherit the Stars.

[fideloper]

Or it's unique properties + earth's in combination are the only reason why life exists.

[SoftwareMaven]

There are theories putting Mars in that position: that early on, Mars was more hospitable due to less water, and microbes eventually caught a ride on something ejected from Mars via volcano or meteor impact.

[ChuckMcM]

"Theia, baseball of God" sounds like a good title :-)