[g__day (Matthew)]

If you want the summary answers too - just say! For the easy ones:

How close was the Moon to Earth when the dinosaurs where alive - would tides have been monumental then and how would it have affected life on Earth?

The first stable orbit for the Moon after its initial formation was likely around 20,000 km (for the impact / capture model). Dinosaurs where around circa a few billion years after that - so simply work on a recession rate of 4 inches a year for 300 million years back from where the moon is today. This means the moon would likely be about 30,000 km closer to the Earth when Dinosaurs roamed then it was today (around 10% closer). Gravity falls away with a square of distance effect - so gravity might have be 19% stronger - tides may have been 19% larger.


Explain why if Jupiter and/or Saturn weren't in our solar system complex life evolving on Earth might not have been possible.

They would have sucked up rogue comets, asteriods and debris that would have been plentiful when early life was forming. If they hadn't many Earth Level Extinction Events could well have wiped out life on Earth. So in essence they act like giant vaccuum cleaners removing dangerous objects left around after solar system formation.


Explain why if our solar system was further in or further out on our galactic arm - complex life would have been at greatly increased risk to survive?

The heart of our galaxy is an exciting place - dangerously exciting. Star formation and termination is rife given the far greater density of stars. These stars go novae sometimes releasing alot of hard radiation - the life killing kinds even at great (astronomical) distances. However radiation helps mutation helps gradual evolution of life. So if our solar system was too far out radiation may not have been strong enough to help create simple life. Too far in and too much activity from supernovae would have sterlised life forming organisms.


Explain why if Earth was about 15% lighter complex life would have been unlikely to survive.

Gravity at the top of our atomsphere would be just a bit weaker and low enough for atomic hydrogen to significantly escape into space. At present over our oceans some water vapour is broken into atomic Hydrogen and Oxygen by ultra violet radiation. But these gases eventually re-combine - so the Earth's atmospheres and its oceans system is stable. For a lighter planet e.g. Mars - gravity is lesser than the critical point where it can retain atomic hydrogen - so eventually it lost all Hydrogen and that means you loose all water too. No water - no medium for life to mix and evolve!