Precambrian names the huge stretch of Earth’s story that comes before the Cambrian time. In older schoolbooks it runs from about 4,600 million years ago — when a hard outer skin of rock first formed on the Earth — to about 570 million years ago.

Precambrian前寒武紀 names指的是 the huge stretch of Earth's story that comes before the Cambrian time地球歷史中，寒武紀之前的一大段時期。In older schoolbooks在較舊的教科書裡 it runs這段時期 from about 4,600 million years ago是從大約四十六億年前 — when a hard outer skin of rock first formed on the Earth那時地球表面才剛形成堅硬的外殼岩石 — to about 570 million years ago一直到大約五億七千萬年前為止。

Though actually, scientists now put the start of the Cambrian nearer 541 million years ago, and they no longer treat “the Precambrian” as one neat period. It is a handy label for almost 90 percent of Earth’s life: the Hadean, Archean, and Proterozoic eons sitting under one umbrella.

Though actually不過其實, scientists now put the start of the Cambrian科學家現在把寒武紀的起點 nearer 541 million years ago訂在比較接近五億四千一百萬年前, and they no longer treat而且他們不再把 the Precambrian「前寒武紀」 as one neat period當成一個乾淨俐落的單一時期。It is a handy label它是一個方便的統稱 for almost 90 percent of Earth's life涵蓋地球生命史裡將近百分之九十的時間: the Hadean, Archean, and Proterozoic eons冥古宙、太古宙和元古宙這三個宙 sitting under one umbrella收在同一把傘下。

The tidy line “that is when simple life first appeared” is tidier than the rocks. Simple life, the kind too small to see, was already here for a very long time; what changes around the Cambrian is that many kinds of animals with hard parts show up clearly in fossils.

The tidy line這句整齊的說法, that is when simple life first appeared「那就是簡單生命第一次出現的時候」, is tidier than the rocks比岩石紀錄本身還要整齊。Simple life簡單生命, the kind too small to see也就是那種小到看不見的生命, was already here for a very long time其實早就存在了很長一段時間; what changes around the Cambrian在寒武紀前後真正改變的 is that many kinds of animals with hard parts是許多有硬殼部位的動物 show up clearly in fossils開始清楚出現在化石紀錄裡。

You use Precambrian as an adjective (Precambrian rock, Precambrian time) and as a name for that whole span (the Precambrian). In careful writing it takes a capital P, because it is a proper name in geology, not a common describing word.

You use Precambrian這個字 as an adjective可以當形容詞用 (Precambrian rock, Precambrian time)（像Precambrian rock前寒武紀岩石、Precambrian time前寒武紀時代） and as a name for that whole span也可以當成那整段時期的名稱 (the Precambrian)（the Precambrian前寒武紀）。In careful writing在講究的寫法裡 it takes a capital P它的P要大寫, because it is a proper name in geology因為在地質學裡它是一個專有名詞, not a common describing word不是普通的形容詞。