Early Earth
This process filled Earth's oceans with water, as the early steam atmosphere cooled off.
What is rain?
What are hydrogen and helium?
These early simple cells did not have a nucleus or organelles.
What are prokaryotes/bacteria?
This organelle evolved to protect DNA by keeping it separated from the rest of the cell.
What is the nucleus?
This simple, filter-feeding organism was one of the first animals on Earth, appearing in the Ediacaran seas about 600 million years ago.
What are sponges?
This invisible shield formed from Earth’s liquid core and protects life from solar radiation.
What is Earth's magnetic field?
This chemical process, used by cyanobacteria, changed the planet forever by adding oxygen to the air.
What is photosynthesis?
This gradual process turned simple molecules into complex, self-replicating systems over millions/billions of years.
What is evolution?
The evolution of photosynthesis allowed life to use this new energy source.
What is sunlight?
This ocean-dwelling arthropod is one of the most famous animals from the Cambrian period.
What are trilobites?
The early atmosphere had plenty of volcanic gases but none of this molecule, which today makes up 21% of Earth's air.
What is oxygen?
These bacteria used sunlight to make food and released oxygen as a waste product.
What are cyanobacteria?
We have no fossils from the earliest life on Earth because of this.
They were small (microscopic cells) and soft. Destroyed immediately.
This step in evolution made it possible for organisms to grow larger and more complex.
What is multicellularity?
These hard parts evolved during the Cambrian and helped animals protect themselves and fossilize more easily.
What are bones and shells?
Before life could survive in the oceans, this problem made the water too harsh for cells to live.
What is the high salinity and metal content of early oceans?
Without oxygen, these energy-producing organelles couldn’t have evolved.
What are mitochondria?
This ancient structure of layered rock shows evidence of some of the first living things.
What are stromatolites?
This is an example of an organelle that evolved through endosymbiosis, when one cell began living inside another in a long-term partnership.
What is the mitochondria or chloroplast?
This term describes the sudden burst of new animal life that began about 541 million years ago.
What is the Cambrian Explosion?
These gases from volcanoes built Earth’s early atmosphere. (name 1)
What are carbon dioxide, methane, and water vapor?
This marks the first major buildup of oxygen in Earth’s air.
What is the Great Oxygenation Event?
This idea says life started as chemistry, not biology — a long process of increasing complexity.
What is abiogenesis?
This new process in some eukaryotes created genetic variety and sped up evolution.
What is sexual reproduction?
This change in Earth’s atmosphere likely made the Cambrian Explosion possible by allowing animals to get more energy.
Increase in oxygen.