Thursday's Assignment: The Geologic Time Scale and Life on Earth

Today you'll be exploring what we know of the history of life on earth, from the beginning of the planet's formation 4.5 billion years ago (= 4,500,000,000 years ago) to the dawn of life (over 2 billion years ago) through all the changes that have lead to the world as we know it today. The understanding of radioactive decay and its use in radiometric dating has allowed scientists to put absolute dates on the fossil record, leading us to a better understanding of when changes took place, and giving us some new insights into how those changes may have occurred.

Your assignment for today is to:

1. Explore the websites below, one at a time.
2. On the geologic timeline handout, record what you learned about major events or changes of life on earth during each of the eras/periods/epochs. Both words and drawings can be helpful in illustrating these details. Be as neat as possible.

Click on the link below and take your time going through the interactive website as you explore geologic time, fossils, and major changes on the earth, taking relevant notes as you go:

Link 1—Geologic Time Interactive

Link 2—Geologic Time Interactive

Helpful Geologic Time Link 1

Helpful Geologic Time Link 2

Please keep your filled-out handout with you—don't turn it in yet. If you need to add to your work at a later time, you can always re-visit this blog to further work through the websites. We'll go over this assignment on Monday.

If you finish before the period is done, work through this interactive site about fossils:

Fossil Interactive Site

Friday's Assignment: Mass Extinctions

Today, you'll be learning more about mass extinctions—the  major events in the history of life on earth where enormous numbers of species went extinct at the same time. Scientists use these mass to divide the earth's history into different time periods, like the ones on the geologic time scale you learned about yesterday.

Here's today's assignment:

1.  First, clink on the link below to read the article and answer questions on the handout:

National Geographic: Mass extinctions article

2.  Next, click on the links below to watch each of these videos about the two biggest mass extinctions of all time. If you have earbuds/headphones, this is the perfect time to use them—plug them in to the CPU and listen to the videos in peace! During/after watching each video, answer the questions on the handout associated with each one.

1st video: Permian-Triassic Mass Extinction: The mother of all die-offs

2nd video: Cretaceous-Tertiary Mass Extinction: Bye-bye, dinosaurs :(

Just like yesterday, take the handout home with you; they'll both be handed in on Monday. If you didn't complete the assignments in class, you can finish them up at home or in the library.

Have a great weekend!

Radioactive Decay & Radiometric Dating

Natural Selction Video: Rock Pocket Mice and Camouflage

Here's a link to the 10-minute video we watched in class:

HHMI Natural Selection Video

Main ideas to focus on:

1) Genetic mutations to the DNA code that cause changes in a trait are random events (they aren't predictable)

2) Once mutations have caused some variation in a trait, the process of natural selection on that trait can occur; Important: Natural selection is not random, but mutations are.

3) Generally, natural selection will predict that individuals with a version of the trait that help them survive and reproduce more than others will have more offspring in the next generation

4) Since the trait is genetic, offspring will inherit the favorable version of the trait from their parents, and each generation more and more individuals will have this version of the trait.

Just So Stories, Lamarck, and Natural Selection

Today we watched an animated version of "The Elephant's Child," one of Rudyard Kipling's Just So Stories from the early 1900s. Here's the link for the 12-minute video:

Elephant's Child animated video

The idea that an individual can change in its lifetime and pass on this change to its ancestors is known as Lamarckism, for its founder, or "Inheritance of Acquired Characteristics." All strange traits can be explained this way, as the adaptation of an elephant's trunk was in the story—stretched out by a predatory crocodile, a trunk was useful, so all elephants after that had long trunks.

Instead, biologists understand that these strange features are brought about by natural selection, a slow process that results in generation-by-generation changes in a trait. Natural selection starts with random genetics mutations that create a new version of the trait that give individuals a survival and/or reproductive advantage. Then, the genes that cause those traits get passed on to more offspring in the next generation.

How could natural selection have worked to fashion an elephant's trunk from ancestors who didn't have a trunk?

2nd assignment: Birds descended from a dinosaur ancestor that had 4 legs and no wings. Describe how birds might have first developed wings:

a) as a "Just So Story."
b) using the step-by-step ideas of natural selection. Thus, rudimentary (basic) wings must have been advantageous, even if they weren't complete like the wings of modern birds.

Important Scientists in the Understanding of Change & Natural Selection