The ice age is a result of shifts in climate. There are many reasons that contribute to the descent into an ice age, but it is believed that the initial forcing is usually due to the Earth's orbital variations on the scale of tens of thousands of years.
we do not know the cause
The past tense is shifted.
Shifted is the past participle.
The light from Andromeda is blue shifted because that galaxy is approaching ours. We will eventually collide, as we have probably done in the past.
Past episodes of BBC Planet Earth can be found in several places. Some of these include Netflix, YouTube, Amazon Instant Video, Hulu Plus, and ITunes.
Could be. It is intentionally left rather vague. But the words of the narrator in several instances indicate that it took place in Earth's distant past.
magnetic field..
He might refer to a primary source, which could be a journal of a past president or other source, to show how past idea's are connected to present events, or several other reasons.
two reasons why is that we need it to know the past
halie
using lots and lots of testing to prove facts about the earth's past.
magnetic field.