Short answers, pulled from the story.
The land bridge known as Doggerland connected Great Britain to mainland Europe until 9,000 years ago. Sea levels rose after the last glacial period to reflood Doggerland by around 6500 BC.
The term Great Britain first appeared officially in 1474 within an instrument proposing marriage between Cecily and James. John Major published his History of Great Britain both England and Scotland in 1521.
Modern humans arrived in Great Britain about 40,000 years ago following the disappearance of Neanderthals. Archaic humans repeatedly occupied the area before abandoning it during cooler periods.
The Acts of Union ratified the Treaty of Union on the 1st of May 1707 merging parliaments of two nations. The treaty specified the name of the new all-island state as Great Britain describing it as One Kingdom.
Rodents make up 40% of mammal species including squirrels mice voles rats and reintroduced European beaver. Carnivorous mammals include red fox Eurasian badger and elusive Scottish wildcat.