Evolution

1. most important element for the development of early life on Earth
3. came up with the theory of natural selection
6. absent in primitive Earth
7. structures that don't serve a purpose now but were important to our ancestors
10. ordered division of organisms into categories based on a set of characteristics used to assess similarities & differences.
12. element used to date fossils based on the length of its half-life
13. idea that species are gradually adapting to their environment
15. animal that Darwin developed the theory of natural selection
17. A change in allele frequencies as a result of this migration of a small subgroup of a population
18. large scale evolution, involving whole taxonomic groups evolving over longer periods of time.

2. explains the origin of eukaryotic cells, mitochondria and chloroplasts used to be bacteria
4. animals adapting based on each others behavior
5. most inclusive, largest general category
8. The act of leaving a habitat or place with the intent of moving to a different habitat or place
9. oxidized and put enough oxygen in the atmosphere for animals to start living on land
11. unintended change in a DNA sequence
14. the evolutionary history of a species or a group of related species
16. the initial common ancestors of all the organisms in a cladogram