Was there a planet named Thera, that collided with earth before the dinosuar time...

[Cloud]

...period? seen it on the discovery channel.

[galadoorquesar]

Today we can see depressions left on earth from many meteroids that have hit the earth. Do you believe that you would see an indent or depression large enough that could of been created by a whole planet? you definetly would. But in the sence of believing maybe our moon is the little bump called Thera.

[Michael Steen]

Most planetary scientists agree that there was a Mars-size body that collided with Earth during it's formation period in the early solar system, and the resulting debris coalesced to form the moon.
This was not only before the dinosaur period, it was before water appeared on Earth. However, there's no name for that now-destroyed planetesimal. If you want to call it Thera, go ahead.

[Harry Hayfield]

Thea (not Thera) was a planet the size of Mars that crashed into the protoEarth. What happened was that both planets were destroyed by the impact (as a result leaving no impact crater) but merged to form the current Earth with some ejecta forming the Moon.