You are almost done with this lesson! Try to complete the passage below. Write your answers on a separate piece of paper.
The earliest life forms on Earth were believed to have existed approximately (1)_____ billion years ago. Pieces of evidence that life forms existed were found in (2)_____, small fossils containing tiny remains of plants and animals. The earliest life forms were believed to be (3)_____ rather than heterotrophs. These organisms are capable of making their own food using sunlight and carbon dioxide from the environment. The first photosynthetic organism was (4)_____. It is from these simple unicellular eukaryotes that multicellular organisms evolved through (5)_____ wherein parts of their cells become complex as each acquires its own function.
On the other hand, scientists including Alexander Oparin and (6)_____ believed that life on Earth originated from a pond or ocean as a result of the combination of chemicals from the atmosphere and some form of energy to make building blocks of proteins. This was later on verified by (7)_____ and Stanley Miller in their experiment wherein they used a gas-filled closed-chamber, applied continuous electric current to it, and demonstrated the formation of (8)_____ after a week. In addition to this experiment, thermal synthesis is done by (9)_____ which used pure and dry amino acids, and intense heating resulted in precipitates in the form of microscopic globules known as (10)_____. Finally, the protocell experiment popularized by (11)_____ claimed that the simplest possible living cells called protocells only required two components to be formed: (12)_____ and lipid sacs
