The difference between “as soon as” or “as early as” is a very fine, nuanced line. In one way, you can use them interchangeably. However, “early” suggests an emphasis on a premature period of time whereas “soon” carries the suggestion of a more immediate future.
So, it is possible to misuse each phrase.
However, it’s nothing to worry about. If you accidentally use the wrong phrase, most people won’t recognize it. That said, you do want to be more conscious of it when writing than with speaking. But, of course, this will largely depend on the context of the subject matter.
As Soon As
When you use the phrase “as soon as,” you’re suggesting the closest possible time. It tends to be vague but it does give the impression of an occurrence in the near future.
I will come over to your house as soon as my sister returns with the car.
As soon as these cookies finish baking, we’ll clean up the kitchen.
She left the movie as soon as the credits finished rolling.
As Early As
“As early as” indicates an emphasis on a specific period of time or it can start the range at the “earliest” possible time. So, you can think of this as being more definite and permanent.
The automobile industry understood the negative effects of gas-powered vehicles as early as the 1970s.
The birds start chirping as early as three or four o’clock in the morning.
As early as the Holocene Era, there were mysterious marauding bands of pirates called “the Sea People.”
Interchanging the Use of Both
While you can interchange “as soon as” with “as early as” and vice versa, there are many situations where it may sound awkward. Alternatively, it could give the wrong impression. Consider the examples already given above and switch the phrases out:
The automobile industry understood the negative effects of gas-powered vehicles as soon as the 1970s.
The birds start chirping as soon as three or four o’clock in the morning.
I will come over to your house as early as my sister returns with the car.
As early as these cookies finish baking, we’ll clean up the kitchen.
She left the movies as early as the credits finished rolling.
As soon as the Holocene Era, there were mysterious marauding bands of pirates called “the Sea People.”
As you can see with the attempt at switching the phrases around that it doesn’t always work or sound right. There are a few situations where it sounds just fine. But there are others that misconstrue the time frame, especially when specifics are involved within the context of the subject matter.
“As soon as” and “as early as” are very similar in meaning but the latter phrase connotes a definitive time whereas the former indicates an estimate. While you can exchange one for the other in some situations, sometimes it will be strange to do so.