Even though fossils of life that existed 3-3.5 billion years
agohave not been found, what
evidence do scientists have that life did exist during this
timeframe?

Fossils are the remains of ancient plants and animals that were buried millions of years back. These are found to be embedded in the sedimentary types of rocks. The earliest known direct fossils are not obtained in the present day, but the imprints of these fossils are explored in many of the places. These were the ancient micro-fossils such as bacterias, cyanobacteria that existed about 3.5 billion years back.

Some of the direct evidence of fossils are obtained from the rocks in the western part of Australia and the southwestern part of Greenland.

Thus, the imprints of these fossils are found in many rocks at different places, and this suggests the existence of life during that particular time frame.

step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.