Final answer:
The earth's early life was simple and aquatic, with prokaryotic cells coming first, followed by more complex eukaryotic cells. Major events such as the Cambrian explosion and mass extinctions have shaped life on earth. Humans have altered the earth's biosphere significantly.
Step-by-step explanation:
The fossil record suggests that early life on earth was simple, unicellular, and primarily existed in water. Fossils can be formed in many ways, including permineralization, carbonization, and mold and casts.
In terms of organism preservation, it's skewed towards marine organisms due to their hard body features like shells or skeletons that tend to fossilize easily compared to soft-bodied organisms. The earth's first inhabitants were prokaryotic cells, which are single-celled organisms lacking a nucleus or other membrane-bound organelles.
Eukaryotic cells are complex with a nucleus and other membrane-bound organelles. This structure allows for a division of labor within the cell, enhancing its survival and reproduction, often said to fuel evolutionary change.
The Cambrian Explosion was a significant event as it led to a rapid diversification of multicellular life, underlining the rise in taxonomy complexity. The Paleozoic era is known for the evolution of fish, the first land-living plants and animals, and the first insects.
In the mid-Paleozoic, continental drift led to supercontinent formation. The increase in free oxygen contributed to the expansion of life on land by making it conducive to life forms.
Carbon dioxide in the atmosphere decreased over time due to photosynthesis and geological factors. This led to the cooling of the earth.
Mass extinctions have altered the course of evolution, by wiping out dominant species, making way for new ones. The Mesozoic era is marked by the dominance of dinosaurs, their extinction theories have changed over time, with asteroid impact now widely accepted.
At the end of the Mesozoic, it's believed that a catastrophic event, possibly an asteroid, led to mass extinction. Rancho La Brea is renowned for the preservation of ice age fossils.
Microfossils provide information about paleoenvironments and climate history. Finally, Darwin's theory of evolution postulates that species evolve over time through natural selection, and the role of humans in modifying the earth's biosphere has become increasingly significant.
Learn more about Evolution and Earth's History