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Diversity - Fossils as Evidence

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Fossils are the preserved remains, impressions, or traces of organisms that lived in the remote past. They serve as direct evidence of the evolutionary process.

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The study of fossils is known as Paleontology.

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Connecting Links: Fossils that possess characters of two different groups of organisms, indicating that one group evolved from the other. For example, Archaeopteryx has features of both reptiles (teeth, long tail) and birds (feathers, wings).

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Estimation of Age (Relative Dating): If we dig into the earth, the fossils found in the deeper layers are generally older than the fossils found in the upper layers.

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Absolute Dating (Carbon Dating): The age of fossils can be determined by detecting the ratio of different isotopes of the same element in the fossil material, commonly using Carbon-14 (14C^{14}C).

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Fossils provide evidence for Phylogeny, which is the evolutionary history or lineage of a species or group of organisms.

📐Formulae

Decay Constant (λ)=ln⁡(2)T1/2≈0.693T1/2\text{Decay Constant } (\lambda) = \frac{\ln(2)}{T_{1/2}} \approx \frac{0.693}{T_{1/2}}

N(t)=N0e−λtN(t) = N_0 e^{-\lambda t}

t=1λln⁡(N0Nt)t = \frac{1}{\lambda} \ln\left(\frac{N_0}{N_t}\right)

Nt=N0(12)n where n=tT1/2N_t = N_0 \left( \frac{1}{2} \right)^{n} \text{ where } n = \frac{t}{T_{1/2}}

💡Examples

Problem 1:

A fossil sample is found to have only 25%25\% of the 14C^{14}C compared to a living sample. If the half-life (T1/2T_{1/2}) of 14C^{14}C is approximately 57305730 years, calculate the age of the fossil.

Solution:

Nt=25% of N0=0.25N0N_t = 25\% \text{ of } N_0 = 0.25 N_0 Using the formula: Nt=N0(12)nN_t = N_0 \left( \frac{1}{2} \right)^{n} 0.25N0=N0(12)n0.25 N_0 = N_0 \left( \frac{1}{2} \right)^{n} 14=(12)n  ⟹  (12)2=(12)n\frac{1}{4} = \left( \frac{1}{2} \right)^{n} \implies \left( \frac{1}{2} \right)^2 = \left( \frac{1}{2} \right)^{n} n=2n = 2 Since n=tT1/2n = \frac{t}{T_{1/2}}, t=n×T1/2=2×5730=11460 yearst = n \times T_{1/2} = 2 \times 5730 = 11460 \text{ years}

Explanation:

The number of half-lives (nn) passed is determined by the ratio of current isotope concentration to initial concentration. Multiplying the number of half-lives by the duration of one half-life gives the total age of the fossil.

Problem 2:

How does the discovery of the Archaeopteryx fossil support the theory of evolution?

Solution:

Archaeopteryx acts as a connecting link. It shows:

  1. Reptilian features: A long bony tail and teeth in the jaw.
  2. Avian (Bird) features: Feathers on the body and wings for flight.

Explanation:

The presence of characters from two distinct classes in a single fossilized organism provides evidence that one class (Aves) evolved from the other (Reptilia).