earlier 与early

用earlier
形容词
1. 早的;提早的;早产的,早熟的
They were much earlier than I expected.
他们比我期待的早多了。
We had an early dinner today.
今天我们晚餐吃得早。
2. 早期的,早先的,在前的
In his early years, he was a keen basketball player.
他早年热衷于打篮球。
3. 不久的,很快的[Z][B]
We look forward to an early reply.
我们期望早日得到答复。
副词ad.
1. 早;提早
Please come to see me early tomorrow morning.
请明天一早来见我。
Please come early.
请早点来。
2. 在开始阶段,在初期
earlier 是early 的比较级
jim always comes earlier than me .指jim比我早

用early正确请看下面两个例句：
I came three hours earlier than the others.
我比其他人早来三小时。
The ship arrived 30 minutes early.
船早到了30分钟。
其实在一个具体的语境中，early和比较级earlier 的区别不用分析很容易看出来。所以“a few hours earlier"和" a few hours early"都是对的，但不能划等号，因为它们使用的语言环境不同，翻译也同中有异。