В ответ на:

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вырубив последнее дерево?

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А вклад лесов в восстановление кислорода ничтожен

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Леса Сибири, по-моему, полезнее лесов Амазонии.

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Phytoplankton are the basis of the ocean food web, and they play a significant role in Earth's climate, since they draw down carbon dioxide, a greenhouse gas, at the same rate as land plants. About half of the oxygen we breathe arises from photosynthesis in the ocean.

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Так что высшие растения, по-видимому, дают около половины.

Можно даже на эту красоту полюбоваться :

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Everything about life on Earth depends on life in the ocean. After all, this is a blue planet, with about 70 percent of the total surface awash with one of the most common molecular compounds known: water.

The oceans regulate the planet's biological wellbeing. But water alone is not enough. Life in its most common forms demands a ready supply of a particular element if it's to thrive: carbon.

It's the same stuff that composes lowly coal, and it's the core of proud tree trunks. Carbon is the root of all life on Earth, and as its complex dance carries it through the biosphere, the Earth's state of health responds.

By monitoring the color of reflected light via satellite, scientists can determine how successfully plant life is photosynthesizing. A measurement of photosynthesis is essentially a measurement of successful growth, and growth means successful use of ambient carbon.

Until now, scientists have only had a continuous record of photosynthesis on land. But following three years of continual data collected by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) instrument, NASA has gathered the first record of photosynthetic productivity in the oceans. The process begins with a measurement of surface chlorophyll concentration.

Chlorophyll is the material that allows plant cells to convert sunlight into energy, thus enabling them to grow. It's a green substance, and thus a good indicator of overall plant health: robust forests and lush lawns and vibrant phytoplankton blooms appear green. By measuring chlorophyll concentration, scientists can determine the health and growth of plants in a given area. By extension, healthy color signatures indicate the successful use of carbon, the fundamental building block for life. In other words, lots of green indicates lots of chlorophyll; lots of chlorophyll implies healthy photosynthesis; strong photosynthesis indicates growth, and growth indicates successful use of carbon.

The above image shows the amount of chlorophyll present in the oceans, and the amount of vegetation on land. Purple and blue represent low levels of chlorophyll, while green, yellow, and red indicate progressively higher concentrations. On land, brown pixels show areas of little vegetation, while blue-green represents dense vegetation.

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После достижения содержания кислорода в атмосфере, равного 0,1 от современного, озоновый экран уже в состоянии полностью защитить организмы от действия жесткой ультрафиолетовой радиации. С этого момента организмы могут начать освоение суши как среды обитания. По расчетам Беркнера и Маршалла, это должно было произойти в конце ордовика (около 420 млн лет назад). Действительно, примерно к этому времени относится появление первых наземных организмов (см. гл. 2). (По мнению ряда других ученых, содержание кислорода в атмосфере соответствующее 10% от современного, было достигнуто уже к началу кембрия, примерно 580 млн лет назад).
Современное содержание кислорода в атмосфере было достигнуто в конце пермского периода.

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