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3.2.2.1: The Fossil Record as Evidence for Evolution - Biology


Fossils tell us when organisms lived, as well as provide evidence for the progression and evolution of life on earth over millions of years.

Learning Objectives

  • Synthesize the contributions of the fossil record to our understanding of evolution

Key Points

  • Fossils are the preserved remains or traces of animals, plants, and other organisms from the past.
  • Fossils are important evidence for evolution because they show that life on earth was once different from life found on earth today.
  • Usually only a portion of an organism is preserved as a fossil, such as body fossils (bones and exoskeletons ), trace fossils (feces and footprints), and chemofossils (biochemical signals).
  • Paleontologists can determine the age of fossils using methods like radiometric dating and categorize them to determine the evolutionary relationships between organisms.

Key Terms

  • biomarker: A substance used as an indicator of a biological state, most commonly disease.
  • trace fossil: A type of fossil reflecting the reworking of sediments and hard substrates by organisms including structures like burrows, trails, and impressions.
  • fossil record: All discovered and undiscovered fossils and their placement in rock formations and sedimentary layers.
  • strata: Layers of sedimentary rock.
  • fossiliferous: Containing fossils.

What Fossils Tell Us

Fossils are the preserved remains or traces of animals, plants, and other organisms from the past. Fossils range in age from 10,000 to 3.48 billion years old. The observation that certain fossils were associated with certain rock strata led 19th century geologists to recognize a geological timescale. Like extant organisms, fossils vary in size from microscopic, like single-celled bacteria, to gigantic, like dinosaurs and trees.

Permineralization

Permineralization is a process of fossilization that occurs when an organism is buried. The empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater. Minerals precipitate from the groundwater, occupying the empty spaces. This process can occur in very small spaces, such as within the cell wall of a plant cell. Small-scale permineralization can produce very detailed fossils. For permineralization to occur, the organism must be covered by sediment soon after death, or soon after the initial decay process.

The degree to which the remains are decayed when covered determines the later details of the fossil. Fossils usually consist of the portion of the organisms that was partially mineralized during life, such as the bones and teeth of vertebrates or the chitinous or calcareous exoskeletons of invertebrates. However, other fossils contain traces of skin, feathers or even soft tissues.

Trace Fossils

Fossils may also consist of the marks left behind by the organism while it was alive, such as footprints or feces. These types of fossils are called trace fossils, or ichnofossils, as opposed to body fossils. Past life may also leave some markers that cannot be seen but can be detected in the form of biochemical signals; these are known as chemofossils or biomarkers.

The Fossil Record

The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossil-containing) rock formations and sedimentary layers (strata) is known as the fossil record. The fossil record was one of the early sources of data underlying the study of evolution and continues to be relevant to the history of life on Earth. The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or “absolute” age of various strata and their included fossils.

Evidence for Evolution

Fossils provide solid evidence that organisms from the past are not the same as those found today; fossils show a progression of evolution. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. This approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years.


How Fossil Evidence Supports Evolution

When you hear talk of evidence for evolution, the first thing that frequently comes to mind for most people is fossils. The fossil record has one important, unique characteristic: it is our only actual glimpse into the past where common descent is proposed to have taken place. As such it provides invaluable evidence for common descent. The fossil record is not "complete" (fossilization is a rare event, so this is to be expected), but there is still a wealth of fossil information.


Fossil Record Web Activity - 2 days

I tell students that they will be working with their elbow partner, and instruct students to the right to gather their computers. Students on the left will be the day's recorders, so they must gather the the Evidence Chart.

I then instruct the computer students to navigate to the UCMP/Berkeley Stories from the Fossil Record website. I explain that as they move through the four "stories", they must discuss what the evidence they are being provided means. The recorder will then write their agreed upon answer on the evidence chart. I tell the students that they will have the rest of the class period to begin their exploration, but that they will continue the work on the site the next day.

Note to teachers: Although the students could complete the modules independently, I find that having one "device" student and one "recorder" tends to foster better discussions as they proceed through the activity. This gives the students a better opportunity to collaborate with a peer to find the best explanation (SP7), and engage in scientific discussions (SP8). I find it useful to collect the evidence charts, even though they are unfinished, just in case the partner that takes it home is absent the next day.

As students come in for the second day, I play the Symphony of Science's video The Greatest Show on Earth. As it is playing, I have students that were recorders the day before get their computers, and distribute the evidence charts to today's recorders. Once the music stops, I tell students that they will continue the previous day's work, and that it must be finished by the ten minute bell.

While the students are working, I am circulating the room, ensuring that the recorders are accurately recording the conversation. I am also interviewing partnerships asking them to explain what they are recording, giving me an opportunity to see how well students can communicate their findings (SP8).

In the first part of this video, you can see snippets of the conversation I have with the students. In the second part, I asked the students what they see as benefits and challenges of working with a partner on this type of activity, which prompted a later conversation about strategies to help each other stay on task.

The student work (SW1, SW2, SW3) lets me know that the students were able to recognize the different pieces of evidence and construct explanations based on them (SP6). This is one of the things I really like about using this website, as it provides clear explanations that the students can follow, and allows them to make connections between the different lines of evidence observed.


Isn’t It Great to Be a Christian and Recognize God’s Purpose in Creation?

As Bible-believing Christians, we can gladly recognize the obvious that there is overwhelming evidence of intelligent design and purpose in God’s creation. Some evolutionists concede that they are aware of this evidence for design, but as the Bible says, they “suppress the truth in unrighteousness” (Romans 1:18). No better example of this suppression of the truth can be seen than the ardent atheist/evolutionist Richard Dawkins who wrote in the first page of his book titled The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe Without Design:

Dawkins concedes that this obvious appearance of design in biological systems cries out for some kind of explanation:

But the only explanation the atheist evolutionist can offer is that somehow nature “counterfeits” intelligent design. How sad.


Watch the video: Evolution - Der Stammbaum des Lebens (January 2022).