The first cells must have been simple, single-celled organisms ...

[Mimi]

The first cells must have been simple, single-celled organisms similar to modern _______________.
 
  Fill in the blank(s) with correct word

Question 2

_______________ are fossilized remains of colonies of single-celled organisms that built up layer after layer of trapped sediments.
 
  Fill in the blank(s) with correct word

[mirabriestensky]

Answer to Question 1

bacteria

Answer to Question 2

Stromatolites

[Mimi]

Thanks for the timely response, appreciate it

[okolip]

Gracias!