Question

1. what evidence best supports the presence of atmospheric oxygen 2.7 billion years ago? layered iron rust in rocks fossils found in stomatolites carbon 14 in plants organic material in meteorites

Explanation:

To determine the best evidence for atmospheric oxygen 2.7 billion years ago, we analyze each option:

• "Layered iron rust in rocks": Iron rusts (oxidizes) in the presence of oxygen. Banded iron formations (layered iron - oxide rocks) formed around 2.7 billion years ago, indicating oxygen was present to oxidize iron.
• "Fossils found in stromatolites": Stromatolites show early life, but not direct evidence of atmospheric oxygen.
• "Carbon - 14 in plants": Carbon - 14 dating is for more recent times (up to ~50,000 years) and not relevant to 2.7 billion years ago.
• "Organic material in meteorites": This relates to extraterrestrial organic matter, not Earth's atmospheric oxygen at 2.7 billion years ago.

Answer:

A. layered iron rust in rocks