Biology (B)

Lesson Summary

• During the 1800s, geologists, paleontologists and naturalists found several forms of physical evidence that confirmed that the earth is very old.
• Fossils of ancient sea life on dry land far from oceans supported the idea that the earth changed over time and that some dry land today was once covered by oceans.
• The many layers of rock represent the order in which rocks and fossils appeared.
• Indications that volcanic eruptions, earthquakes and erosion that happened long ago shaped much of the earth’s surface.
• Radiometric dating allows scientists to measure the age of rocks by measuring the radioactivity of certain minerals in rocks.
• The oldest rock minerals found on Earth so far are zircon crystals that are at least 4.404 billion years old.
• Some of the oldest fossils of life forms on Earth are at least 3.5 billion year old fossils of blue green algae found in Australia.
• Scientists believe the early earth contained no oxygen gas, but did contain other gases, including nitrogen, carbon dioxide, carbon monoxide, water vapor, hydrogen sulfide and probably a few others.
• Geologists and other earth scientists use geologic time scales to describe when events occurred throughout the history of Earth.
• The geological time scale of Earth's past is organized according to events which took place during different periods on the time scale.
• Life on Earth began about 3.5 to 4 billion years ago.
• The first life forms were single cell organisms, prokaryotic organisms, similar to bacteria.
• The first multicellular organisms did not appear until about 610 million years ago in the oceans. Some of the first multicellular forms included sponges, brown algae, and slime molds.
• Plants and fungi appeared roughly 500 million years ago. They were soon followed by arthropods (insects and spiders).
• Amphibians evolved about 300 million years ago, followed by mammals around 200 million years ago and birds around 100 million years ago.
• Extinction of species is common; in fact, it is estimated that 99% of the species that have lived on the earth no longer exist.
• Mass extinctions, such as the extinction of dinosaurs and many marine mammals, happened after major catastrophes such as volcanic eruptions and major earthquakes changed the environment.
• There have been at least five major massive extinctions have occurred in the past 540 million years.
• In each mass extinction, over 50% of animal species died.