1. the first forms of life on earth were
a. plants
b. microorganisms
c. birds
d. dinosaurs
2. a suggested and testable explanation for an event is called a
a. hypothesis
b. variable
c. theory
d. control
3. which of the following sciences is not considered a natural science?
a. biology
b. astronomy
c. physics
d. computer science

The population of bacteria in a petri dish doubles every 40 seconds. the population of the bacteria is initially 400 organisms. what unit is most appropriate for the time at which the number of bacteria is 300? hour bacteria per hour second bacteria per second

Sydney drew a flow chart to illustrate the nitrogen cycle.which labels best complete the flow chart? x: producers undergo photosynthesis.y: nitrogen compounds are released into the air.x: nitrogen compounds are released into the air.y: producers undergo photosynthesis.x: free nitrogen is in the atmosphere.y: producers absorb nitrogen compounds through their roots.x: producers absorb nitrogen compounds through their roots.y: free nitrogen is in the atmosphere.

Match each term to its best definition? sedimentary depositional enviornment