There are two different types of bracket: round (like this - the kind Americans call parentheses) or square [like this]. They are used for different purposes.

In Earth Science, round brackets are used mainly for additional information, often for formula, figures, measurements or dates.

For example:

• The Hadeon Eon (Hades is the Greek word for hell) is the earliest eon.
• The Paleozoic era (291 million years) lasted longer than the Mesozoic and Cenozoic eras combined.
• Aristotle (384-322 BCE) was the father of classical logic.
  

Brackets should be used very sparingly, though. If a piece of information is worth putting into an essay, brackets are usually unnecessary.

Square brackets are used to enclose information about graphs or diagrams, for example:

• [Fig. 6: oceanic plates subduction zone]

Square brackets can also be used to enclose the word [sic], from the Latin sicut, meaning 'just as'. We use this in quotations to show that any grammatical, punctuation or spelling errors in the quotation directly mirror the quotation and were not our own. For example:

• Aristotle declared that there were five elements: "fire, earth, air, water and aether [sic]".