Our Changing Earth - 4.6 billion years of change
One of the most challenging concepts in Earth science is that of geologic time. The landscape you see around you today is not permanent, nor has it ever been. It is in a constant state of change, and has been since the Earth's inception 4.6 billion years ago. Our human lives, however, are so short compared to the age of the Earth, that it often seems to us as though nothing ever changes. In reality, change occurs at different rates at scales; from slow and steady movements of the continents measured in only a few millimeters per year to sudden, catastrophic events like the meteorite that is theorized to have hit the Earth near the modern Yucatan Peninsula in Mexico around 65 million years ago (and is blamed for the extinction of the dinosaurs and about 60% of the total number of species on Earth at the time).
If you scaled the entire history of the Earth onto a football field, you can see how short the time of humans has been on Earth. Imagine standing at the back of the end zone on one end of the football field. Reach down and place the tip of your finger on the very edge of the white line that marks the back of the endzone (like you are pointing at the line). The thickness of your fingernail is about the length of human history on Earth.
The graphic below from your textbook outlines the key periods of Earth's history. Use it and your textbook to answer the questions that follow.
If you scaled the entire history of the Earth onto a football field, you can see how short the time of humans has been on Earth. Imagine standing at the back of the end zone on one end of the football field. Reach down and place the tip of your finger on the very edge of the white line that marks the back of the endzone (like you are pointing at the line). The thickness of your fingernail is about the length of human history on Earth.
The graphic below from your textbook outlines the key periods of Earth's history. Use it and your textbook to answer the questions that follow.
1. The first multi-celled organisms formed just over a billion years ago. Given the timeline and order of development during the Paleozoic period, do you think the first multi-celled organisms likely developed in the marine (oceans) or the terrestrial (on land) environment? Why?
2. The boundary between the Permian and the Triassic periods is marked by an event called the Permian-Triassic extinction about 252 million years ago. During this event (which scientists think lasted several thousand years), over 96% of marine life and over 70% of terrestrial species went extinct. Based on these percentages, do you think the degree and speed of change was greater in the oceans or on land? (Hint: think about what causes a species to go extinct even today: rapid change or slow change?)
3. We are currently in the Holocene epoch, a relatively warm period between ice ages. According to the figure, the Holocene began about 0.01 million years ago. How many years ago is that? What percentage of the Earth's entire history is the Holocene period? Do this math on your own first, then see the video below for the answer.
2. The boundary between the Permian and the Triassic periods is marked by an event called the Permian-Triassic extinction about 252 million years ago. During this event (which scientists think lasted several thousand years), over 96% of marine life and over 70% of terrestrial species went extinct. Based on these percentages, do you think the degree and speed of change was greater in the oceans or on land? (Hint: think about what causes a species to go extinct even today: rapid change or slow change?)
3. We are currently in the Holocene epoch, a relatively warm period between ice ages. According to the figure, the Holocene began about 0.01 million years ago. How many years ago is that? What percentage of the Earth's entire history is the Holocene period? Do this math on your own first, then see the video below for the answer.