Biology · Rung 4 of 4

The origin of life

For evolution to begin all you need is something that copies itself with occasional mistakes: that alone gives heredity, variation and selection. The most-worked hypothesis is that RNA played the part, since it can both store information and speed up reactions, two trades now split between DNA and proteins. LUCA is the last universal common ancestor, the organism from which the bacterium, the mushroom and you descend; that it existed is not an assumption, it follows from every living thing using the same genetic code. What surprises most about the history of life is not the order but the spacing: from the first cells to nucleated ones took some two billion years. And when photosynthesis filled the air with oxygen it caused the largest known extinction, because oxygen was a poison to almost everything then alive.

Where this sits

Comes after
Natural selection

Exercises from this rung

Generated by the app, from easiest to hardest

  1. What had to appear first for evolution to start?

    • A molecule able to copy itself
    • A nucleus to keep the information in
    • A cell with its complete membrane
    • Oxygen in the atmosphere

    Why Something that copied itself with occasional mistakes: that alone gives heredity, variation and selection, which is everything evolution needs. The most-worked hypothesis is that RNA played the part, since it can both store information and speed up reactions, two trades now split between DNA and proteins.

    easier

  2. How old are the oldest known traces of life?

    • Some 65 million years
    • Some 500 million years
    • Some 4.5 billion years
    • Some 3.5 billion years

    Why Almost as old as the habitable Earth: only a few hundred million years after there were oceans. That is what makes many people think life appears readily wherever there is liquid water and chemistry. What took an age was not starting, it was getting from one cell to two.

    in between

  3. When photosynthesis filled the air with oxygen, what happened?

    • It was a poison that killed almost everything alive
    • The air warmed and the poles melted
    • Life multiplied everywhere straight away
    • Nothing changed until animals arrived

    Why The largest extinction in history, and life itself caused it. Oxygen is highly reactive and wrecked organisms used to living without it; the survivors hid where it did not reach or learned to use it, and using it turned out to give five times more energy. Everything large alive today came out of that.

    harder